pi_agent_rust

pi_agent_rust - High-performance AI coding agent CLI written in Rust

Why Should You Care? • TL;DR • Methodology • Quick Start • Features • Installation • Commands • Configuration

# Install latest release
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/install.sh?$(date +%s)" | bash

The Problem

You want an AI coding assistant in your terminal, but existing tools are:

Slow to start: Node.js/Python runtimes add 500ms+ before you can type
Memory hungry: Electron apps or heavy runtimes eat gigabytes
Unreliable: Streaming breaks, sessions corrupt, tools fail silently
Hard to extend: Closed ecosystems or complex plugin systems

The Solution

pi_agent_rust is a from-scratch Rust port of Pi Agent by Mario Zechner (made with his blessing!). Single binary, instant startup, stable streaming, and 8 built-in tools.

Rather than a direct line-by-line translation, this port builds on two purpose-built Rust libraries:

asupersync: A structured concurrency async runtime with built-in HTTP, TLS, and SQLite
rich_rust: A Rust port of Rich by Will McGugan, providing beautiful terminal output with markup syntax

# Start a session
pi "Help me refactor this function to use async/await"

# Continue a previous session
pi --continue

# Single-shot mode (no session)
pi -p "What does this error mean?" < error.log

Why Should You Care?

If you already use Pi Agent, especially through OpenClaw, this project keeps the core workflow while upgrading the engine under the hood:

Substantially faster in realistic end-to-end flows (not synthetic microbenchmarks)
Dramatically smaller memory footprint in long-running sessions
Materially stronger security model for extension/tool execution, including command-level blocking of dangerous extension shell patterns

Security is a first-class design goal here, not a bolt-on:

Capability-gated hostcalls (tool/exec/http/session/ui/events)
Two-stage extension exec enforcement: capability gate first, then command mediation that blocks critical shell classes by default (for example recursive delete, disk/device writes, reverse shell) and can tighten to block high-tier classes in strict/safe policy
Policy + runtime risk + quota enforcement on the execution path
Per-extension trust lifecycle (pending -> acknowledged -> trusted -> killed) with kill-switch audit logs and explicit operator provenance
Hostcall-lane emergency controls that can force compatibility-lane execution globally or for one extension when fast-lane behavior needs immediate containment
Structured concurrency via asupersync for more predictable cancellation/lifecycle behavior
Auditable runtime signals/ledgers and redacted security alerts for extension behavior

TL;DR (Pi/OpenClaw Users)

These are the realistic secure-path numbers that matter most (large-session, end-to-end behavior):

Scenario	Rust total	Legacy Node total	Legacy Bun total	Rust advantage
Realistic 1M session	250.29 ms	1,238.67 ms	700.52 ms	`4.95x` faster than Node, `2.80x` faster than Bun
Realistic 5M session	1,382.12 ms	5,974.67 ms	2,959.42 ms	`4.32x` faster than Node, `2.14x` faster than Bun

(from tests/perf/reports/budget_summary.json, run 20260423T002033Z)

Scenario	Rust RSS	Legacy Node RSS	Legacy Bun RSS	Rust memory advantage
Realistic 1M session	67,572 KB	820,380 KB	875,092 KB	`12.14x` lower than Node, `12.95x` lower than Bun
Realistic 5M session	268,844 KB	2,173,096 KB	3,057,908 KB	`8.08x` lower than Node, `11.37x` lower than Bun

(from tests/perf/reports/PERF_BUDGETS.md, run 20260423T002033Z)

Resume/open responsiveness is also much better at scale:

Scenario	Rust open	Legacy Node open	Legacy Bun open	Rust advantage
1M session resume	17.59 ms	119.76 ms	50.83 ms	`6.81x` faster than Node, `2.89x` faster than Bun
5M session resume	58.68 ms	396.41 ms	155.63 ms	`6.76x` faster than Node, `2.65x` faster than Bun

(from tests/perf/reports/budget_events.jsonl, run 20260423T002033Z)

Extension runtime guarantees are also concrete:

Extension assurance signal	Why you should care
Two-stage `exec` guard (`exec` capability policy + command-level mediation + DCG/heredoc AST signals)	Dangerous shell intent is caught before spawn, including destructive payloads hidden in multiline wrappers
Trust lifecycle + kill switch (`pending/acknowledged/trusted/killed`)	You can quarantine an extension instantly, log who pulled the switch and why, and require explicit re-acknowledgement before restoring access
Hostcall lane kill-switch controls (`forced_compat_global_kill_switch`, `forced_compat_extension_kill_switch`)	Fast-path regressions can be contained immediately by forcing compatibility-lane execution without disabling the extension system
Deterministic hostcall reactor mesh (shard affinity, bounded SPSC lanes, backpressure telemetry, optional NUMA slab tracking)	Runtime behavior stays predictable under contention; queue pressure and routing decisions are observable instead of opaque
Startup prewarm + warm isolate reuse for JS runtimes	Runtime creation overlaps startup and warm reuse keeps repeated extension runs low-latency without a Node/Bun process model
Tamper-evident runtime risk ledger (`verify` / `replay` / `calibrate`)	Security decisions are hash-linked and can be replayed or threshold-tuned from real runtime traces

Bottom line: for real Pi/OpenClaw usage, the Rust version is faster, far more memory-efficient, and materially stronger on extension runtime safety under real workload pressure.

_{Data source: docs/planning/BENCHMARK_COMPARISON_BETWEEN_RUST_VERSION_AND_ORIGINAL__GPT.md (latest secure-path + full orchestrator checkpoints, 2026-04-23).}

README Citation Convention

All numeric performance claims in this README include inline citations with format: *(from [artifact-path], run [correlation-id])*

Example: *(from tests/perf/reports/budget_summary.json, run 20260423T002033Z)*

This ensures claims are verifiable against specific test runs and prevents stale numbers from persisting across updates.

How We Made It So Fast

In this README, we means the project owner and collaborating coding agents.
The speed gains come from runtime design, not one trick.

Technique	What we do	Runtime effect
Cold-start minimization	Single static binary, no Node/Bun runtime bootstrap, no JIT warmup, startup prewarm for extension runtime paths	Faster time-to-first-interaction
Less copying on hot paths	`Arc`/`Cow` message flow, zero-copy hostcall/tool payload handling, reduced clone-heavy provider/session paths	Lower CPU and allocation pressure
Deterministic dispatch core	Typed hostcall opcodes, fast-lane/compat-lane routing, bounded shard queues with reactor-mesh telemetry	Better tail latency under concurrent extension load
Efficient long-session storage	SQLite session index + v2 sidecar (segmented log + offset index) with O(index+tail) reopen path	Fast resume on large histories
Streaming parser tuned for real networks	SSE parser tracks scanned bytes, handles UTF-8 tails, normalizes chunk boundaries, interns event-type strings	Lower streaming overhead and fewer parser stalls
Safe fast-path controls	Shadow dual execution sampling, automatic backoff on divergence/overhead, compatibility-lane kill switches for containment	Keeps optimizations fast without silent behavior drift
CI-level performance governance	Scenario matrices, strict artifact contracts, fail-closed perf gates	Regressions are caught before release

If you want the full implementation inventory, see Performance Engineering.

Benchmark Methodology and Claim Integrity

The benchmarks cited above are intentionally designed to be realistic, reproducible, and hard to game.

What we measured:

Matched-state workloads: resume a large session and append the same 10 messages.
Realistic E2E workloads: resume + append + extension activity + slash-style state changes + forks + exports + compactions.
Scale levels: from 100k up to 5M token-class session states.
Startup/readiness: command-level readiness (--help, --version) separately from long-session workflows.

How we kept comparisons fair:

Two scopes in the benchmark report:
- apples-to-apples (pi_agent_rust vs legacy coding-agent)
- apples-to-oranges (legacy stack components included where legacy behavior is outsourced)
Release-mode binaries and repeated runs per matrix cell.
No paid-provider noise in core latency/footprint tables (provider-call costs are excluded from these core comparisons).

How we kept claims honest:

Security controls stayed on during secure-path measurements (no policy/risk/quota bypasses for speed claims).
Raw artifacts are preserved (JSON/trace/time outputs) and called out in the benchmark report.
Blockers are explicitly disclosed: when direct legacy reruns were blocked by missing workspace deps, we state that and compare against prior validated legacy artifacts instead of pretending reruns succeeded.
Interpretation notes are explicit: the report distinguishes baseline sections vs fresh reruns so readers can see exactly which values came from which run set.
Reproducibility over marketing: methodology, caveats, and known limits are included alongside wins.

If you want full details, see:

docs/planning/BENCHMARK_COMPARISON_BETWEEN_RUST_VERSION_AND_ORIGINAL__GPT.md (methodology + results + caveats + raw artifact paths)

Why Pi?

Feature	Pi (Rust)	Typical TS/Python CLI
Startup	<100ms	500ms-2s
Binary size	~44MB (default features)	100MB+ (with runtime)
Memory (idle)	<50MB	200MB+
Streaming	Native SSE parser	Library-dependent
Tool execution	Process tree management	Basic subprocess
Sessions	JSONL with branching	Varies
Unsafe code	Forbidden	N/A

Quick Example

# 1) Start an interactive session
pi

# 2) Ask a codebase question
pi "Summarize the architecture in src/"

# 3) Attach a file inline
pi @src/main.rs "Explain startup flow"

# 4) Run single-shot mode for scripting
pi -p "List likely regression risks for this diff"

# 5) Continue your last project session
pi --continue

# 6) Inspect available models/providers
pi --list-models
pi --list-providers

Foundation Libraries

asupersync

asupersync is a structured concurrency async runtime designed for applications that need predictable resource cleanup. Key features used by pi_agent_rust:

Capability-based context (Cx): Async functions receive an explicit context that controls what they can do (HTTP, filesystem, time). This makes testing deterministic.
HTTP client with TLS: Built-in HTTP API with rustls, avoiding OpenSSL dependency hell
Structured cancellation: When a parent task cancels, all child tasks cancel cleanly. No orphaned futures.

pi_agent_rust runs on asupersync end-to-end today (runtime + HTTP/TLS + cancellation). Provider streaming uses a minimal HTTP client (src/http/client.rs) feeding a custom SSE parser (src/sse.rs).

rich_rust

rich_rust is a Rust port of Will McGugan's Rich Python library. It provides:

Markup syntax: [bold red]error[/] renders as bold red text
Tables: ASCII/Unicode table rendering with alignment and borders
Panels: Boxed content with titles
Progress bars: Animated progress indicators
Markdown: Terminal-rendered markdown with syntax highlighting
Themes: Consistent color schemes across components

The terminal UI uses rich_rust for all output formatting, providing the same visual quality as Rich-based Python tools.

Quick Start

1. Install

# Install latest release binary
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/install.sh?$(date +%s)" | bash

If you already have the original TypeScript pi installed, the installer asks whether to make Rust Pi canonical as pi and automatically create legacy-pi for the old command.

2. Configure API Key

export ANTHROPIC_API_KEY="sk-ant-..."

3. Run

# Interactive mode
pi

# With an initial message
pi "Explain this codebase structure"

# Read files as context
pi @src/main.rs "What does this do?"

Features

Streaming Responses

Real-time token streaming with extended thinking support:

pi "Write a quicksort implementation"

Watch the response appear token-by-token, with thinking blocks shown inline.

8 Built-in Tools

Tool	Description	Example
`read`	Read file contents, supports images	Read src/main.rs
`write`	Create or overwrite files	Write a new config file
`edit`	Surgical string replacement	Fix the typo on line 42
`hashline_edit`	Precise edits using LINE#HASH tags	Apply edits to specific lines using hashline anchors
`bash`	Execute shell commands with timeout	Run the test suite
`grep`	Search file contents with context	Find all TODO comments
`find`	Discover files by pattern	Find all *.rs files
`ls`	List directory contents	What's in src/?

All tools include:

Automatic truncation for large outputs (2000 lines / 1MB)
Detailed metadata in responses
Process tree cleanup for bash (no orphaned processes)

Session Management

Sessions persist as JSONL files with full conversation history:

# Continue most recent session
pi --continue

# Open specific session
pi --session ~/.pi/agent/sessions/--home-user-project--/2024-01-15T10-30-00.jsonl

# Ephemeral (no persistence)
pi --no-session

Sessions support:

Tree structure for conversation branching
Model/thinking level change tracking
Automatic compaction for long conversations

Extended Thinking

Enable deep reasoning for complex problems:

pi --thinking high "Design a distributed rate limiter"

Thinking levels: off, minimal, low, medium, high, xhigh

Customization (Skills & Prompt Templates)

Skills: Drop SKILL.md under ~/.pi/agent/skills/ or .pi/skills/ and invoke with /skill:name.
Prompt templates: Markdown files under ~/.pi/agent/prompts/ or .pi/prompts/; invoke via /<template> [args].
Packages: Share bundles with pi install npm:@org/pi-packages (skills, prompts, themes, extensions).

Autocomplete

Pi provides context-aware autocomplete in the interactive editor:

@ file references: Type @ followed by a path fragment to attach file contents. The completion engine indexes project files (respecting .gitignore) via the ignore crate's WalkBuilder, capping at 5,000 entries.
/ slash commands: Built-in commands (/help, /model, /tree, /clear, /compact, /exit) and user-defined prompt templates and skills all appear as completions.
Fuzzy scoring: Prefix matches rank above substring matches. Results are sorted by match quality, then by kind (commands > templates > skills > files > paths).
Background refresh: A background thread re-indexes the project file tree every 30 seconds, so completions stay current without blocking the input loop.

Three Execution Modes

Pi runs in three modes, each suited to different workflows:

Mode	Invocation	Use Case
Interactive	`pi` (default)	Full TUI with streaming, tools, session branching, autocomplete
Print	`pi -p "..."`	Single response to stdout, no TUI, scriptable
RPC	`pi --mode rpc`	Headless JSON protocol over stdin/stdout for IDE integrations

Interactive mode provides the full experience: a multi-line text editor with history, scrollable conversation viewport, model selector (Ctrl+L), scoped model cycling (Ctrl+P/Ctrl+Shift+P), session branch navigator (/tree), and real-time token/cost tracking.

Print mode sends one message, streams the response to stdout, and exits. Useful for shell scripts and one-off queries.

RPC mode exposes a line-delimited JSON protocol for programmatic control. Clients send commands (prompt, steer, follow-up, abort, get-state, compact) and receive streaming events. This is how IDE extensions and custom frontends integrate with Pi. See RPC Protocol for the wire format.

Extensions

Pi supports two extension runtime families with capability-gated host connectors:

JS/TS entrypoints run without Node or Bun in an embedded QuickJS runtime.
*.native.json descriptors run in the native-rust descriptor runtime.
Extension entrypoints are auto-detected:
- .js/.ts/.mjs/.cjs/.tsx/.mts/.cts run directly in embedded QuickJS (no descriptor conversion).
- *.native.json loads the native-rust descriptor runtime.
- One session currently uses one runtime family at a time (JS/TS or native descriptor).
Sub-100ms cold load (P95), sub-1ms warm load (P99)
Node API shims for fs, path, os, crypto, child_process, url, and more
Capability-based security: extensions call explicit connectors (tool/exec/http/session/ui) with audit logging
Command-level exec mediation: dangerous shell signatures are classified and blocked before spawn, with redacted denial alerts and mediation ledger entries
Trust-state lifecycle and kill-switch controls with audited state transitions (pending/acknowledged/trusted/killed)
Hostcall reactor mesh with deterministic shard routing, bounded queue backpressure, and optional NUMA-aware telemetry
Runtime prewarm path with warm isolate reuse so extension startup cost is mostly paid before the first prompt

Credential-Aware Model Selection

/model (or Ctrl+L) opens a selector focused on models that are ready to run with current credentials.
Ctrl+P and Ctrl+Shift+P cycle through the scoped model set without opening the overlay.
Provider IDs and aliases are matched case-insensitively in model selection and /login.
Models that do not require configured credentials can run keyless.

Extensions can register tools, slash commands, event hooks, flags, providers, and shortcuts. See EXTENSIONS.md for the full architecture and docs/extension-catalog.json for the 223-entry catalog with per-extension conformance status and perf budgets.

Extension Validation Pipeline

This project validates extension compatibility with a three-track pipeline:

Vendored corpus (224): deterministic conformance, compatibility matrix, and scenario suites.
Unvendored corpus (777): source acquisition and onboarding prioritization.
Release-binary live-provider E2E: real target/release/pi execution against a non-mocked provider/model path.

Why this exists

Catch runtime/API regressions in QuickJS host shims and capability policy.
Catch dangerous extension shell call patterns with real command mediation on the release binary path.
Verify extension behavior against real provider responses, not just fixture/mocked flows.
Keep extension support measurable instead of anecdotal.
Produce a prioritized queue for onboarding unvendored candidates into vendored conformance.

Pipeline components

Fetch unvendored source corpus
- Binary: ext_unvendored_fetch_run
- Typical command:
  - cargo run --example ext_unvendored_fetch_run -- run-all --workers 8 --no-probe
- Purpose:
  - Clones GitHub repos and unpacks npm tarballs into .tmp-codex-unvendored-cache/
  - Produces machine-readable acquisition status for all unvendored candidates
- Artifacts:
  - tests/ext_conformance/reports/pipeline/unvendored_fetch_probe_report.json
  - tests/ext_conformance/reports/pipeline/unvendored_fetch_probe_events.jsonl
Run end-to-end validation orchestration
- Binary: ext_full_validation
- Typical command:
  - cargo run --example ext_full_validation --
- Stages (in order):
  1. refresh_onboarding_queue (runs ext_onboarding_queue)
  2. conformance_shard_0..N (runs ext_conformance_generated sharded matrix)
  3. conformance_failure_dossiers
  4. provider_compat_matrix
  5. scenario_conformance_suite
  6. auto_repair_full_corpus
  7. differential_suite (optional, enabled via --run-diff; npm diff via --run-npm-diff)
- Artifacts:
  - tests/ext_conformance/reports/pipeline/full_validation_report.json
  - tests/ext_conformance/reports/pipeline/full_validation_report.md
  - Plus stage-specific reports under tests/ext_conformance/reports/**
Run dev-firstset live-provider gate (must pass before release build)
- Binary: ext_release_binary_e2e
- Typical command:
  - cargo build --bin pi --bin ext_release_binary_e2e
  - PI_HTTP_REQUEST_TIMEOUT_SECS=0 target/debug/ext_release_binary_e2e --pi-bin target/debug/pi --provider ollama --model qwen2.5:0.5b --jobs 10 --timeout-secs 600 --max-cases 20 --extension-policy balanced --out-json tests/ext_conformance/reports/release_binary_e2e/ollama_firstset_dev_20260219_jobs10_timeout600.json --out-md tests/ext_conformance/reports/release_binary_e2e/ollama_firstset_dev_20260219_jobs10_timeout600.md
- Purpose:
  - Proves the current codepath works end-to-end on a representative first-set before paying release-build cost.
  - Serves as the promotion gate to full release-binary validation.
- Gate:
  - Require pass=20 / total=20 with fail=0.
- Artifacts:
  - tests/ext_conformance/reports/release_binary_e2e/ollama_firstset_dev_20260219_jobs10_timeout600.json
  - tests/ext_conformance/reports/release_binary_e2e/ollama_firstset_dev_20260219_jobs10_timeout600.md
Run full release-binary live-provider E2E (after step 3 passes)
- Binary: ext_release_binary_e2e
- Typical command:
  - cargo build --release --bin pi --bin ext_release_binary_e2e
  - PI_HTTP_REQUEST_TIMEOUT_SECS=0 target/release/ext_release_binary_e2e --pi-bin target/release/pi --provider ollama --model qwen2.5:0.5b --jobs 10 --timeout-secs 600 --extension-policy balanced --out-json tests/ext_conformance/reports/release_binary_e2e/ollama_full_release_20260219_jobs10_timeout600.json --out-md tests/ext_conformance/reports/release_binary_e2e/ollama_full_release_20260219_jobs10_timeout600.md
- Purpose:
  - Executes target/release/pi directly for each selected extension case.
  - Uses a live provider/model path (default ollama + qwen2.5:0.5b) to exercise non-mocked end-to-end behavior.
  - Emits per-case stdout/stderr captures plus summary artifacts (pi.ext.release_binary_e2e.v1).
- Artifacts:
  - tests/ext_conformance/reports/release_binary_e2e/ollama_full_release_20260219_jobs10_timeout600.json
  - tests/ext_conformance/reports/release_binary_e2e/ollama_full_release_20260219_jobs10_timeout600.md
  - tests/ext_conformance/reports/release_binary_e2e/cases/*
Aggregate and triage
- full_validation_report.json combines:
  - Stage-level pass/fail (stageSummary, stageResults)
  - Corpus counts (corpus)
  - Vendored conformance totals (conformance)
  - Provider matrix totals (providerCompat)
  - Scenario totals (scenario)
  - Review queue + verdict classification (reviewQueue, verdictCounts)
- Important interpretation rule:
  - not_tested_unvendored indicates unvendored candidates not yet in vendored conformance; this is inventory status, not a vendored regression.

Recommended run environment

These runs compile many crates and can be disk-heavy. Point Cargo artifacts and temp files to a large volume:

export CARGO_TARGET_DIR="/data/tmp/pi_agent_rust_cargo/${USER:-agent}/target"
export TMPDIR="/data/tmp/pi_agent_rust_cargo/${USER:-agent}/tmp"
mkdir -p "$CARGO_TARGET_DIR" "$TMPDIR"

Then run:

cargo run --example ext_unvendored_fetch_run -- run-all --workers 8 --no-probe
cargo run --example ext_full_validation --

Latest run snapshot (2026-05-01)

From:

tests/ext_conformance/reports/gate/must_pass_gate_verdict.json (generated 2026-05-01T03:20:54.460Z, run local-20260501T0316)
tests/ext_conformance/reports/health_delta/health_delta_report.json (generated 2026-05-01T04:10:28.479Z)
tests/ext_conformance/reports/journeys/journey_report.json (generated 2026-05-01T04:07:47.106Z)
tests/evidence_bundle/index.json (generated 2026-05-01T04:19:19.979Z, run local-20260501T0413)
tests/full_suite_gate/certification_verdict.json (generated 2026-05-01T04:35:30.643Z, run local-20260501T0442)
docs/evidence/dropin-certification-verdict.json (generated 2026-05-01T04:35:52Z)
Strict drop-in status: 20/20 certification gates PASS, 14/14 blocking gates PASS - CERTIFIED (from docs/evidence/dropin-certification-verdict.json; strict replacement wording is allowed only while this verdict remains CERTIFIED and the contract hard gates stay PASS)
Unified evidence bundle: 28/28 sections present, 11/11 required sections present, 0 missing, 0 invalid (from tests/evidence_bundle/index.json)
Extension must-pass gate: 123/123 must-pass extensions passed; informational stretch set 98/101 passed (from tests/ext_conformance/reports/gate/must_pass_gate_verdict.json)
Extension health delta: 221/224 current extensions passed (98.7%), 0 regressions, 34 fixes vs the 2026-02-07 baseline (from tests/ext_conformance/reports/health_delta/health_delta_report.json)
Extension journey coverage: 87/123 journey scenarios passed (70.7%); command, passive, and tool-provider categories are green, while event-subscriber journeys remain tracked as current failures (from tests/ext_conformance/reports/journeys/journey_report.json)
Stress triage: 1,500 events, 0 errors, p99 latency 576us, RSS growth 0.0% (from tests/perf/reports/stress_triage.json, generated 2026-05-01T03:28:52Z)

Installation

Curl Installer (Recommended)

# Latest release
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/install.sh?$(date +%s)" | bash

# Non-interactive + auto PATH update
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/install.sh?$(date +%s)" | bash -s -- --yes --easy-mode

# Pin a release tag
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/install.sh?$(date +%s)" | bash -s -- --version v0.1.0

# Install from explicit artifact URL + checksum URL
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/install.sh?$(date +%s)" | \
  bash -s -- \
    --artifact-url "https://github.com/Dicklesworthstone/pi_agent_rust/releases/download/v0.1.0/pi-linux-amd64.tar.xz" \
    --checksum-url "https://github.com/Dicklesworthstone/pi_agent_rust/releases/download/v0.1.0/SHA256SUMS"

# Skip completion setup (CI/non-interactive minimal install)
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/install.sh?$(date +%s)" | \
  bash -s -- --yes --no-completions

The installer is idempotent and supports a migration path from TypeScript Pi:

Detect existing TS pi command
Prompt to install Rust Pi as canonical pi
Preserve old CLI behind legacy-pi
Record state for clean uninstall/restore

Notable installer flags:

--offline [TARBALL]: enforce offline mode; optional local artifact path (.tar.gz, .tar.xz, .zip, or raw binary)
--artifact-url: force a specific release artifact URL
--checksum / --checksum-url: override checksum source for explicit artifacts
--sigstore-bundle-url: override Sigstore bundle URL used by cosign verify-blob
--completions auto|off|bash|zsh|fish: force shell completion install target (off is equivalent to --no-completions)
--no-completions: disable completion installation
--no-agent-skills: skip automatic installation of the pi-agent-rust skill into ~/.claude/skills/ and ~/.codex/skills/
--no-verify: skip checksum + signature verification (testing only)
--artifact-url without --version uses a synthetic tag for release mode only; if artifact download fails, install exits instead of attempting source fallback
Installer honors HTTPS_PROXY / HTTP_PROXY for all network fetches

By default, the installer also installs a pi-agent-rust skill for both Claude Code and Codex CLI:

Claude Code: ~/.claude/skills/pi-agent-rust/SKILL.md
Codex CLI: ~/.codex/skills/pi-agent-rust/SKILL.md (or $CODEX_HOME/skills/pi-agent-rust/SKILL.md if CODEX_HOME is set)
During upgrades, installer-managed legacy pre-tool entries from older versions are removed automatically (idempotent, path-scoped, and non-destructive) when prior installer state is present.

Installer regression harness (options + checksum + signature + completions):

bash tests/installer_regression.sh

Distribution Compatibility Contract (Packaging/Invocation Scope)

For migration adoption, packaging and invocation compatibility follows this contract:

This section covers packaging/invocation behavior only; functional parity and certification status are tracked in docs/contracts/dropin-certification-contract.json.
Canonical executable name is pi across release assets and installer-managed installs.
Installer-managed installs also create an rpi compatibility launcher when no conflicting rpi command already exists on your PATH.
Existing TypeScript pi installs can be migrated in place; the prior command is preserved as legacy-pi.
If you keep TypeScript pi as canonical (--keep-existing-pi), Rust Pi is installed as pi-rust.
On Apple Silicon, the installer prefers the native arm64 artifact even when launched from a Rosetta-translated shell.
Version-pinned installs are supported via install.sh --version vX.Y.Z for deterministic rollouts.
Every GitHub release ships platform binaries plus SHA256SUMS for integrity validation.

Representative smoke checks:

# Canonical command should exist and execute
command -v pi
pi --version
pi --help >/dev/null

# If a TS migration was performed, legacy command remains available
command -v legacy-pi && legacy-pi --version

From Source

Requires Rust nightly (2024 edition features):

# Install Rust nightly
rustup install nightly
rustup default nightly

# Clone and build
git clone https://github.com/Dicklesworthstone/pi_agent_rust.git
cd pi_agent_rust
cargo build --release

# Binary is at target/release/pi
./target/release/pi --version

# To install system-wide (--locked ensures reproducible dependency resolution)
cargo install --path . --locked

Dependencies

Pi has minimal runtime dependencies:

fd: Required for the find tool (install via apt install fd-find or brew install fd)
rg: Required for the grep tool (install via apt install ripgrep or brew install ripgrep)

Uninstall

curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi_agent_rust/main/uninstall.sh" | bash

By default, uninstall removes installer-managed Rust binaries/aliases and skill directories, then restores a migrated TypeScript pi if one was preserved.

Commands

Basic Usage

pi [OPTIONS] [MESSAGE]...

# Examples
pi                              # Start interactive session
pi "Hello"                      # Start with message
pi @file.rs "Explain this"      # Include file as context
pi -p "Quick question"          # Print mode (no session)

Interactive file references:

Type @relative/path in the editor to attach a file’s contents (autocomplete inserts the @ form).

Options

Option	Description
`-c, --continue`	Continue most recent session
`-r, --resume`	Open session picker UI
`--session <PATH>`	Open specific session file
`--session-dir <DIR>`	Override session storage directory for this run
`--session-durability strict	balanced
`--no-session`	Don't persist conversation
`-p, --print`	Single response, no interaction
`--mode text	json
`--provider <NAME>`	Force provider for this run (aliases supported)
`--model <MODEL>`	Model to use (auto-select fallback: `anthropic/claude-sonnet-4-6`, then `anthropic/claude-opus-4-7`, then `openai/gpt-5.1-codex`)
`--thinking <LEVEL>`	Thinking level: off/minimal/low/medium/high/xhigh
`--tools <TOOLS>`	Comma-separated tool list
`--api-key <KEY>`	API key (or use provider-specific env vars such as `ANTHROPIC_API_KEY`, `OPENAI_API_KEY`, etc.)
`--extension-policy safe	balanced
`--repair-policy off	suggest
`--list-models [PATTERN]`	List available models (optional fuzzy filter)
`--list-providers`	List canonical provider IDs, aliases, and auth env keys
`--export <PATH>`	Export session file to HTML

Additional high-leverage flags:

--no-migrations to skip startup migration checks
--explain-extension-policy to print effective capability decisions and exit
--explain-repair-policy to print effective repair-policy resolution and exit

Subcommands

# Package management
pi install <source> [-l|--local]    # Install a package source and add to settings
pi remove <source> [-l|--local]     # Remove a package source from settings
pi update [source]                 # Update all (or one) non-pinned packages
pi list                            # List user + project packages from settings

# Configuration
pi config                          # Show settings paths + precedence

More utility subcommands:

# Extension catalog index + discovery
pi update-index
pi search "git"
pi info pi-search-agent

# Environment and extension diagnostics
pi doctor
pi doctor --only sessions --format json
pi doctor ./path/to/extension --policy safe --fix

# Session storage migration (JSONL -> v2 sidecar store)
pi migrate ~/.pi/agent/sessions --dry-run
pi migrate ~/.pi/agent/sessions

update-index refreshes extension index metadata used by search and info.
search and info let you discover and inspect extension metadata without leaving the CLI.
doctor checks config, directories, auth, shell setup, sessions, and extension compatibility.
migrate validates or creates the v2 session sidecar format for faster resume on larger histories.

Configuration

Pi reads configuration from ~/.pi/agent/settings.json:

{
  "default_provider": "anthropic",
  "default_model": "claude-opus-4-5",
  "default_thinking_level": "medium",

  "compaction": {
    "enabled": true,
    "reserve_tokens": 8192,
    "keep_recent_tokens": 20000
  },

  "retry": {
    "enabled": true,
    "max_retries": 3,
    "base_delay_ms": 1000,
    "max_delay_ms": 30000
  },

  "images": {
    "auto_resize": true,
    "block_images": false
  },

  "terminal": {
    "show_images": true,
    "clear_on_shrink": false
  },

  "shell_path": "/bin/bash",
  "shell_command_prefix": "set -e"
}

Configuration Precedence

Settings are resolved in priority order (first match wins):

CLI flags (--model, --thinking, --provider, etc.)
Environment variables (ANTHROPIC_API_KEY, PI_CONFIG_PATH, etc.)
Project settings (.pi/settings.json in the working directory)
Global settings (~/.pi/agent/settings.json)
Built-in defaults

This means a CLI flag always overrides a settings.json value, and a project-level setting overrides the global one.

Resource Resolution

Skills, prompt templates, themes, and extensions follow the same resolution order:

CLI-specified paths (--skill, --prompt-template, --theme, -e)
Project directory (.pi/skills/, .pi/prompts/, .pi/themes/, .pi/extensions/)
Global directory (~/.pi/agent/skills/, ~/.pi/agent/prompts/, etc.)
Installed packages (~/.pi/agent/packages/)

When multiple resources share the same name, the first occurrence wins. Collisions are logged as diagnostics.

Prompt template expansion supports positional arguments: $1, $2, $@ (all args), and slice syntax ${@:start}, ${@:start:length}. For example, a template invoked as /review src/main.rs --strict receives src/main.rs as $1 and --strict as $2.

Environment Variables

Variable	Description
`ANTHROPIC_API_KEY`	Anthropic API key
`OPENAI_API_KEY`	OpenAI API key
`GOOGLE_API_KEY`	Google Gemini API key
`AZURE_OPENAI_API_KEY`	Azure OpenAI API key
`COHERE_API_KEY`	Cohere API key
`GROQ_API_KEY`	Groq API key (OpenAI-compatible)
`DEEPINFRA_API_KEY`	DeepInfra API key (OpenAI-compatible)
`CEREBRAS_API_KEY`	Cerebras API key (OpenAI-compatible)
`OPENROUTER_API_KEY`	OpenRouter API key (OpenAI-compatible)
`MISTRAL_API_KEY`	Mistral API key (OpenAI-compatible)
`MOONSHOT_API_KEY`	Moonshot/Kimi API key (OpenAI-compatible)
`DASHSCOPE_API_KEY`	DashScope/Qwen API key (OpenAI-compatible)
`DEEPSEEK_API_KEY`	DeepSeek API key (OpenAI-compatible)
`FIREWORKS_API_KEY`	Fireworks API key (OpenAI-compatible)
`TOGETHER_API_KEY`	Together API key (OpenAI-compatible)
`PERPLEXITY_API_KEY`	Perplexity API key (OpenAI-compatible)
`XAI_API_KEY`	xAI API key (OpenAI-compatible)
`PI_CONFIG_PATH`	Custom config file path
`PI_CODING_AGENT_DIR`	Override the global config directory
`PI_PACKAGE_DIR`	Override the packages directory
`PI_SESSIONS_DIR`	Custom sessions directory

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                           CLI (clap)                            │
│  • Argument parsing    • @file expansion    • Subcommands       │
└─────────────────────────────────┬───────────────────────────────┘
                                  │
┌─────────────────────────────────▼───────────────────────────────┐
│                          Agent Loop                             │
│  • Message history     • Tool iteration    • Event callbacks    │
└────────┬──────────────────────┬──────────────────────┬──────────┘
         │                      │                      │
┌────────▼────────┐  ┌─────────▼──────────┐  ┌───────▼──────────┐
│ Provider Layer  │  │  Tool Registry     │  │  Extension Mgr     │
│ • Anthropic     │  │  • read  • bash    │  │  • QuickJS JS/TS   │
│ • OpenAI (Chat/ │  │  • write • grep    │  │  • Native descriptor│
│   Responses)    │  │  • edit  • find    │  │    runtime          │
│ • Gemini/Cohere │  │  • ls              │  │  • Capability policy│
│ • Azure/Bedrock │  │  • ext-registered  │  │  • Node shims       │
│ • Vertex/Copilot│  │                    │  │  • Event hooks      │
│ • GitLab/Ext    │  │                    │  │  • Runtime risk ctl │
└────────┬────────┘  └─────────┬──────────┘  └───────┬──────────┘
         │                     │                      │
┌────────▼─────────────────────▼──────────────────────▼──────────┐
│                     Session Persistence                         │
│  • JSONL format (v3)   • Tree structure   • Session index/cache  │
│  • Per-project dirs    • Default-enabled SQLite backend support │
└─────────────────────────────────────────────────────────────────┘

Provider-count rule: Pi has 10 native provider implementation modules, counted as the Rust files under src/providers/ excluding mod.rs. Those modules are anthropic, openai, openai_responses, gemini, cohere, azure, bedrock, vertex, copilot, and gitlab. User-visible provider IDs, aliases, OpenAI-compatible presets, and extension-provided streamSimple providers are counted separately because several native modules expose multiple routes.

Key Design Decisions

No unsafe code: #![forbid(unsafe_code)] enforced project-wide
Streaming-first: Custom SSE parser, no blocking on responses
Process tree management: sysinfo crate ensures no orphaned processes
Structured errors: thiserror with specific error types per component
Speed-oriented release profile: LTO + strip + opt-level = 3 for runtime performance

asupersync Context vs TypeScript Pi (pi-mono)

This Rust port preserves Pi's user experience, but intentionally changes the runtime substrate. The original TypeScript Pi (pi-mono, packages/coding-agent) is built on Node.js + package-level abstractions. pi_agent_rust moves those same behaviors onto asupersync primitives so lifecycle guarantees are explicit in the runtime model.

Concern	TypeScript Pi (pi-mono baseline)	pi_agent_rust + asupersync
Runtime model	Node event loop + Promise/AbortSignal conventions	`RuntimeBuilder` + explicit reactor and runtime handle
Async ownership	Task lifetimes coordinated by framework/library code	Structured task ownership and explicit cross-thread channels (TUI/RPC bridging)
Cancellation semantics	Primarily API- and tool-layer conventions	Runtime-aware cancellation checks + bounded timeout handling in tools
I/O capability shape	Ambient Node APIs + extension layer policies	Capability-scoped context (`AgentCx` over `asupersync::Cx`) and explicit hostcall policy
HTTP streaming	Provider/client dependent	Purpose-built asupersync HTTP/TLS client feeding custom SSE parser
Deterministic test hooks	Conventional async test setup	asupersync test/runtime hooks used widely in unit/integration tests

Why this is useful in practice:

More predictable failure behavior during aborts/timeouts because cancellation is checked in explicit loop boundaries and tool runners.
Cleaner resource lifetimes because the runtime, timers, and I/O paths all share one concurrency substrate.
Less hidden coupling because the main invariants live in Rust types/algorithms rather than spread across framework conventions.

Runtime Invariants (and Why They Matter)

These are the concrete invariants we rely on in this implementation:

Turn-scoped agent lifecycle
- The main loop emits AgentStart, TurnStart, TurnEnd, and AgentEnd in a stable order.
- Tool recursion is bounded by max_tool_iterations (default 50) to avoid unbounded self-tool loops.
- Benefit: stable event ordering for TUI/RPC consumers and predictable termination behavior.
Abort and timeout behavior is explicit
- Agent abort checks happen at turn boundaries and around tool execution.
- bash timeout follows a clear escalation path: terminate process tree, grace period, then hard kill.
- Benefit: fewer "hung" sessions and reduced orphan-process risk during aggressive tool use.
Session writes are crash-resilient
- JSONL saves write to a temp file and persist atomically.
- Session indexing uses SQLite WAL + lock file coordination for concurrent instances.
- Benefit: better durability and resume reliability under multi-process usage.
Compaction is threshold-driven and boundary-aware
- Trigger: estimated context tokens exceed context_window - reserve_tokens.
- Cut-point logic prefers user-turn boundaries and preserves recent context budget.
- Benefit: compaction recovers context without collapsing near-term task continuity.
Capability policy is fail-closed and precedence-defined
- Resolution order: per-extension deny -> global deny -> per-extension allow -> default caps -> mode fallback.
- Benefit: policy outcomes are explainable, deterministic, and auditable.
Streaming parser tolerates real network chunking
- SSE parser handles CR/LF variants, multi-line data: fields, partial UTF-8 tails, and end-of-stream flush.
- Benefit: incremental rendering remains robust across providers and network fragmentation.

Design Principles Carried From asupersync Into Pi

The following asupersync principles are reflected directly in pi_agent_rust architecture:

Single async substrate: runtime, timers, fs, and HTTP/TLS all run on one coherent foundation.
Explicit context threading: AgentCx wraps asupersync::Cx at subsystem boundaries (agent/tools/session/rpc).
Bounded operations over best-effort cleanup: timeout paths and compaction thresholds are parameterized and enforceable.
Determinism hooks for tests: timer-driver aware sleeps and asupersync test helpers reduce nondeterministic flakiness.

Compared to the original TypeScript implementation, this shifts more correctness responsibility into the runtime and core algorithms themselves, instead of relying primarily on ecosystem conventions.

Additional Major Deltas (Original pi-mono vs Rust Port)

This is a second comparison pass focused on high-impact architectural deltas and rationale.

Area	Original pi-mono (`packages/coding-agent`)	`pi_agent_rust`	Why this divergence exists
Distribution model	npm package (`npm install -g @mariozechner/pi-coding-agent`)	Single Rust binary (`pi`)	Remove Node runtime dependency and improve startup/deployment portability
Execution surfaces	Interactive + print + JSON mode + RPC + SDK	Interactive + print + JSON mode + RPC + Rust SDK	Rust SDK provides idiomatic companion API for embedding Pi programmatically (documented in `docs/sdk.md`)
Default built-in tool posture	Defaults to `read/write/edit/bash` (others available)	Eight built-ins treated as first-class (`read/write/edit/bash/grep/find/ls/hashline_edit`)	Keep common code-navigation, shell, and hashline-anchored edit workflows available without extra configuration
Extension trust model	Extension/package model documented as full system access	Embedded runtime with capability-gated hostcalls and policy profiles	Reduce ambient authority and make extension behavior auditable/deny-by-default
Session architecture emphasis	JSONL tree session model and branch navigation	JSONL v3 tree + explicit session index (SQLite sidecar) + default-enabled SQLite session backend support	Faster resume/lookups at scale and safer multi-instance coordination
Streaming transport stack	Node runtime networking stack	Purpose-built HTTP/TLS client + custom SSE parser on asupersync	Tighter control over chunking, parsing, and failure handling in long streams
Cancellation/timeout mechanics	Platform/event-loop cancellation conventions	Explicit abort signaling, bounded tool iterations, process-tree termination	Minimize hangs/orphans and make stop behavior deterministic under load
Runtime context model	Framework-level conventions and extension APIs	Explicit `AgentCx`/`asupersync::Cx` capability-scoped context threading	Make effect boundaries and testability first-class architectural constraints

Practical consequence of these deltas:

Extension/package workflows are compatible across both implementations.
The goal is functional equivalence to pi-mono with Rust-idiomatic patterns and performance improvements.
The Rust SDK provides a companion API that delivers equivalent capabilities without requiring TypeScript-specific adaptation patterns.
docs/parity-certification.json tracks functional parity progress and certification status.

Algorithmic Mechanics: pi-mono Baseline vs Rust Implementation

This section compares concrete implementation mechanics for equivalent high-level behavior.

Algorithm	pi-mono baseline mechanism	Rust implementation mechanism	Why the Rust variant exists
Session context rebuild after compaction	`buildSessionContext()` emits compaction summary, then messages from `firstKeptEntryId` (pre-compaction path), then post-compaction entries	`to_messages_for_current_path()` uses the same ordering and adds a fallback if `first_kept_entry_id` is missing	Avoid silent context loss when compaction anchors are orphaned/corrupted
JSONL persistence	Incremental append (`appendFileSync`) plus full rewrite (`writeFileSync`) for migrations/rewrites	Save via temp file + atomic persist/replace	Keep on-disk session state crash-resilient during save operations
Session discovery/resume	Directory/file scan and mtime sorting of JSONL files	SQLite session index sidecar + WAL + lock file + staleness-triggered full reindex	Bound resume lookup cost and coordinate concurrent processes
Compaction token accounting	Uses assistant usage (`totalTokens` else `input+output+cacheRead+cacheWrite`) plus heuristic trailing estimates	Uses assistant usage (`total_tokens` else `input+output`) plus heuristic trailing estimates; fixed image token estimate	Keep accounting stable across providers with uneven cache-token reporting while staying conservative
Cut-point + split-turn handling	Valid cut points exclude tool results; split turns are summarized as history + turn-prefix context	Same cut-point class and split-turn strategy, implemented in Rust entry/message model	Preserve tool-call/result adjacency and turn coherence under budget pressure
Bash timeout/process cleanup	Timeout/abort kills process tree (`killProcessTree`) and returns tail-truncated output	Timeout escalation (`TERM` then grace then `KILL`) + process-tree walk + shell exit trap + tail truncation	Enforce bounded cleanup and reduce descendant-process leaks from background jobs
Streaming event decoding	Transport semantics are exposed (`sse`/`websocket`/`auto`); parser details are runtime-internal	Explicit SSE parser with BOM stripping, CR/LF normalization, UTF-8 tail buffering, and flush-on-end	Make byte-to-event behavior deterministic and provider-SDK-independent

Feature Superset Highlights (Beyond pi-mono Baseline)

The sections above compare mechanics. This section calls out concrete features present in this Rust port that are not part of the pi-mono baseline implementation model.

Rust-port feature	Why it is useful/compelling
`pi doctor` diagnostics command (`text`/`json`/`markdown`, `--only`, `--fix`, extension compatibility checks)	Gives actionable environment + compatibility diagnostics, supports CI gating (non-zero on failures), and can auto-fix safe issues like missing dirs/permissions
Capability-gated extension policy profiles (`safe` / `balanced` / `permissive`) with per-extension overrides	Lets operators run shared extensions with explicit capability boundaries instead of ambient full-system access
Secret-aware extension env filtering (`pi.env()` blocklist for keys/tokens/secrets)	Reduces accidental credential exposure from extension code paths
Per-extension trust lifecycle + kill-switch audit trail (`pending`/`acknowledged`/`trusted`/`killed`, `kill_switch`, `lift_kill_switch`)	Supports immediate containment, explicit operator provenance, and controlled re-entry after review
Hostcall compatibility-lane emergency controls (global/per-extension forced-compat switches + reason codes)	Gives operators a deterministic rollback path for fast-lane incidents without losing extension availability
Runtime risk controller for extension hostcalls (configurable, fail-closed by default)	Adds another enforcement layer beyond static policy for suspicious runtime behavior in extension call flows
Argument-aware runtime risk scoring for shell paths (`dcg_rule_hit`, `dcg_heredoc_hit`, heredoc AST inspection across Bash/Python/JS/TS/Ruby)	Detects destructive intent hidden in multiline scripts and wrapper commands before hostcall execution
Tamper-evident runtime risk ledger tooling (`ext_runtime_risk_ledger verify	replay
Unified incident evidence bundle export (risk ledger, security alerts, hostcall telemetry, exec mediation, secret-broker events)	Incident response can triage from one structured artifact set instead of stitching ad-hoc logs
Deterministic hostcall reactor mesh with optional NUMA slab pool (shard affinity, global-order drain, bounded SPSC lanes, telemetry)	Keeps extension dispatch predictable under load and surfaces queue/backpressure behavior for tuning
Warm isolate pool + startup prewarm handoff	Moves JS runtime preparation off the first interactive turn and reuses warmed state safely between runs
Extension preflight static analysis (imports/forbidden-pattern scan with policy-aware hints)	Catches risky extension patterns before runtime execution
Node/Bun-compatible extension runtime without Node/Bun dependency (embedded QuickJS + shims)	Runs legacy extension workflows in a single native binary deployment model
Extension compatibility scanner + conformance harness	Makes extension support measurable and auditable instead of anecdotal
SQLite session index sidecar (WAL + lock + stale reindex path)	Gives fast session resume/list operations at scale without scanning every JSONL file on each query
Session Store V2 rollback and migration ledger (segmented log + checkpoints + rollback events)	Long-session recovery can unwind to a known checkpoint with explicit migration/rollback provenance
Default-enabled SQLite session storage support (`sqlite-sessions` feature)	Supports deployments that want database-backed session persistence in addition to JSONL; disable with `--no-default-features` when building a minimal binary
Crash-resilient session save path (temp file + atomic persist)	Improves session-file durability during writes and reduces partial-write failure modes
Unified hostcall dispatcher with typed taxonomy mapping (`timeout` / `denied` / `io` / `invalid_request` / `internal`)	Produces consistent extension/runtime error semantics and easier client handling
Fail-closed evidence-lineage gates (`run_id`/`correlation_id` + cross-artifact lineage checks)	Rejects stale or cherry-picked conformance/perf artifacts at release-gate time
Structured auth diagnostics with stable machine codes	Improves troubleshooting and operational visibility without leaking sensitive credential material

Deep Dive: Core Algorithms

Math-Driven Decision Systems

Pi deliberately uses advanced math where it improves runtime behavior or benchmark confidence. The goal is not “fancy formulas in docs”; it is safer policy decisions, faster recovery from workload shifts, and more trustworthy performance attribution.

Regime-Shift Detection (CUSUM + BOCPD)

In the extension dispatcher, Pi combines CUSUM and Bayesian online change-point detection to detect load-regime changes early (for example when hostcall traffic suddenly spikes or stalls).

$$ S_t^+ = \max\left(0,;S_{t-1}^+ + (-z_t - k)\right), \quad S_t^- = \max\left(0,;S_{t-1}^- + (z_t - k)\right) $$

$$ H(r)=\frac{1}{\lambda}, \quad P(r_t=0 \mid x_{1:t}) \propto \sum_r P(r_{t-1}=r),H(r),P(x_t \mid r) $$

Intuition: CUSUM catches persistent drift; BOCPD catches sudden regime changes without brittle fixed thresholds.

Conformal Prediction Envelope

Pi tracks nonconformity scores (absolute residuals from the running mean) and treats out-of-interval events as anomalies.

$$ q = \text{score}_{\lceil (n+1)\cdot \text{confidence} \rceil - 1}, \quad \text{anomaly if } |x_t - \mu_t| > q $$

Intuition: thresholds adapt from recent behavior instead of hard-coding one static latency cutoff.

PAC-Bayes Safety Bound

Pi’s safety envelope includes a PAC-Bayes-kl bound over extension outcomes, and can veto aggressive optimization when the bound is too high.

$$ \mathrm{kl}(\hat q ,|, q_{\text{bound}});\le;\frac{\mathrm{KL}(Q|P)+\ln!\left(2\sqrt{n}/\delta\right)}{n} $$

Intuition: this gives an explicit uncertainty-aware ceiling on true error risk before allowing more aggressive runtime behavior.

Off-Policy Evaluation (IPS/WIS/DR + ESS + Regret Gate)

Before approving policy moves, Pi evaluates candidate behavior from trace data:

$$ w_i=\frac{\pi(a_i\mid x_i)}{\mu(a_i\mid x_i)}, \quad \hat V_{\text{IPS}}=\frac{1}{n}\sum_i w_i r_i $$

$$ \hat V_{\text{WIS}}=\frac{\sum_i w_i r_i}{\sum_i w_i}, \quad \hat V_{\text{DR}}=\frac{1}{n}\sum_i\left(\hat r_i + w_i(r_i-\hat r_i)\right) $$

$$ N_{\text{eff}}=\frac{(\sum_i w_i)^2}{\sum_i w_i^2}, \quad \Delta_{\text{regret}}=\bar r_{\text{baseline}}-\hat V_{\text{DR}} $$

Intuition: Pi fails closed if sample support is weak, uncertainty is high, or estimated regret is above threshold.

VOI-Driven Experiment Selection

The VOI planner prioritizes probes that provide the most expected learning under a strict overhead budget.

$$ \text{priority}_i \propto \frac{\text{utility}_i}{\text{overhead}_i} $$

Intuition: run only the experiments that are likely to change decisions; skip stale or low-value probes.

Weighted Bottleneck Attribution (Benchmarking)

For phase-1 matrix benchmarking, Pi computes stage attribution weighted by realistic workload size (session_messages) and reports confidence intervals.

$$ \text{weighted_contribution}_s

\frac{\sum_i w_i,m_{i,s}}{\sum_i w_i,t_i}\cdot 100, \quad w_i=\text{session_messages}_i $$

$$ n_{\text{eff}}=\frac{(\sum_i w_i)^2}{\sum_i w_i^2}, \quad \mathrm{CI}_{95}=\mu \pm 1.96\sqrt{\frac{\sigma^2}{n_{\text{eff}}}} $$

Intuition: prioritize what dominates real end-to-end latency, not just isolated microbench hotspots.

Online Convex Control + Regret Tracking

Pi also includes an online tuner path for batch/time-slice controls with explicit rollback behavior:

$$ \tau_{t+1}

\mathrm{clip}!\left(\tau_t - \eta\nabla_{\tau}\mathcal{L}t,;\tau{\min},\tau_{\max}\right) $$

Intuition: the system adapts continuously, but if instantaneous loss exceeds a rollback threshold it immediately returns to a safer profile.

Math At a Glance

Technique	Where in Pi	Why it helps
CUSUM + BOCPD	Extension dispatcher regime detector	Detects traffic regime shifts early and robustly
Conformal intervals	Safety envelope	Adaptive anomaly gating without static magic numbers
PAC-Bayes bound	Safety envelope veto path	Fails closed when uncertainty/risk is too high
IPS/WIS/DR + ESS	Off-policy evaluator	Approves policy changes only with adequate support
VOI planning	Experiment scheduler	Uses overhead budget on highest-value probes
Weighted attribution + CI	Phase-1 perf matrix reports	Ranks optimization work by realistic user impact
OCO + regret rollback	Runtime controller	Adapts under load while bounding unsafe drift

SSE Streaming Parser

The SSE (Server-Sent Events) parser is a custom implementation that handles Anthropic's streaming response format. Unlike library-based approaches, the parser operates as a state machine that processes bytes incrementally:

Bytes → Line Accumulator → Event Parser → Typed StreamEvent

Key characteristics:

Property	Implementation
Buffering	Zero-copy where possible; lines accumulated only when incomplete
Event types	12 distinct variants: MessageStart, ContentBlockStart, ContentBlockDelta, ContentBlockStop, MessageDelta, MessageStop, Ping, Error, and thinking-specific events
Error recovery	Malformed events logged but don't crash the stream
Memory	Fixed-size rolling buffer prevents unbounded growth

The parser handles edge cases like:

Multi-line data: fields (concatenated with newlines)
Events split across TCP packet boundaries
The event: field appearing before or after data:
CRLF and LF line endings interchangeably

Truncation Algorithm

Large outputs from tools (file reads, command output, grep results) must be truncated to avoid exhausting the LLM's context window. The truncation algorithm preserves usefulness while staying within limits:

┌─────────────────────────────────────────┐
│           Original Content              │
│         (potentially huge)              │
└─────────────────────────────────────────┘
                    │
                    ▼
┌─────────────────────────────────────────┐
│  HEAD: First N/2 lines                  │
│  ─────────────────────────              │
│  [... X lines truncated ...]            │
│  ─────────────────────────              │
│  TAIL: Last N/2 lines                   │
└─────────────────────────────────────────┘

Constants:

Limit	Value	Rationale
`MAX_LINES`	2000	Balances context usage vs. completeness
`MAX_BYTES`	1MB	Prevents binary file accidents
`GREP_MAX_LINE_LENGTH`	500 chars	Truncates minified code

The algorithm:

Splits content into lines
If line count exceeds MAX_LINES, takes first 1000 and last 1000
Inserts a marker showing how many lines were omitted
If byte count still exceeds MAX_BYTES, applies byte-level truncation
Returns metadata indicating truncation occurred, enabling the LLM to request specific ranges

Process Tree Management

The bash tool must handle runaway processes, infinite loops, and fork bombs without leaving orphans. The implementation uses the sysinfo crate to walk the process tree:

// Pseudocode for process cleanup
fn kill_process_tree(root_pid: Pid) {
    let system = System::new();
    let children = find_all_descendants(root_pid, &system);

    // Kill children first (deepest first), then parent
    for child in children.iter().rev() {
        kill(child, SIGKILL);
    }
    kill(root_pid, SIGKILL);
}

Timeout behavior:

Command starts with configurable timeout (default 120s)
Output streams to a rolling buffer in real-time
On timeout: SIGTERM sent, 5s grace period, then SIGKILL
Process tree walked and all descendants killed
Exit code set to indicate timeout vs. normal termination

To avoid orphaned background jobs (e.g. cmd &), the bash script installs an EXIT trap that waits for any remaining child processes and then exits with the original command's status.

This prevents the common failure mode where killing a shell leaves its children running.

Session Tree Structure

Sessions use a tree structure rather than a flat list, enabling conversation branching (useful when exploring different approaches):

                    ┌─────────┐
                    │ Message │ (root)
                    │   #1    │
                    └────┬────┘
                         │
                    ┌────▼────┐
                    │ Message │
                    │   #2    │
                    └────┬────┘
                         │
              ┌──────────┼──────────┐
              │                     │
         ┌────▼────┐          ┌────▼────┐
         │ Message │          │ Message │ (branch)
         │   #3    │          │   #3b   │
         └────┬────┘          └────┬────┘
              │                    │
         ┌────▼────┐          ┌────▼────┐
         │ Message │          │ Message │
         │   #4    │          │   #4b   │
         └─────────┘          └─────────┘

JSONL format (v3):

Each line is a self-contained JSON object with a type discriminator:

{"type":"session","version":3,"cwd":"/project","created":"2024-01-15T10:30:00Z"}
{"type":"message","id":"a1b2c3d4","parent":"root","role":"user","content":[...]}
{"type":"message","id":"e5f6g7h8","parent":"a1b2c3d4","role":"assistant","content":[...]}
{"type":"model_change","id":"i9j0k1l2","parent":"e5f6g7h8","model":"claude-sonnet-4-20250514"}

The parent field creates the tree. Replaying a session walks the tree from root to the current leaf. Branching creates a new message with a different parent than the previous continuation.

Provider Abstraction

The Provider trait abstracts over different LLM backends:

#[async_trait]
pub trait Provider: Send + Sync {
    fn name(&self) -> &str;
    fn models(&self) -> &[Model];

    async fn stream(
        &self,
        context: &Context,
        options: &StreamOptions,
    ) -> Result<impl Stream<Item = Result<StreamEvent>>>;
}

Context structure:

pub struct Context {
    pub system: Option<String>,      // System prompt
    pub messages: Vec<Message>,       // Conversation history
    pub tools: Vec<ToolDef>,          // Available tools with JSON schemas
}

StreamOptions:

pub struct StreamOptions {
    pub model: String,
    pub max_tokens: u32,
    pub temperature: Option<f32>,
    pub thinking: Option<ThinkingConfig>,  // Extended thinking settings
    pub stop_sequences: Vec<String>,
}

This design allows adding new providers (OpenAI, Gemini) without modifying the agent loop. Each provider translates the common types to its wire format and emits a unified StreamEvent stream.

Compaction Algorithm

Long conversations eventually exceed the model's context window. Pi's compaction algorithm reclaims space by summarizing older messages while preserving recent context.

The algorithm runs automatically after each agent turn when estimated token usage exceeds context_window - reserve_tokens:

┌──────────────────────────────────────────────────────────────┐
│                     Full Conversation                         │
│  msg1 → msg2 → msg3 → ... → msgN-5 → msgN-4 → ... → msgN   │
│  ├──── older messages ─────┤ ├─── recent messages ──────────┤ │
│                                                              │
│  Step 1: Find cut point at a valid turn boundary             │
│  Step 2: LLM summarizes msgs 1..N-5 into compact paragraph  │
│  Step 3: Store Compaction entry in session JSONL             │
│  Step 4: Next agent call uses [summary] + msgs N-4..N       │
└──────────────────────────────────────────────────────────────┘

Token estimation uses a conservative chars ÷ 4 heuristic for text and a flat 1,200 tokens per image. When an assistant message includes a usage field from the API, that measured value takes precedence over the heuristic.

Cut point selection prefers boundaries between complete user-assistant turns. If the budget forces a mid-turn cut, the algorithm includes prefix messages from the split turn so the model retains context about what was being discussed at the boundary.

File operation tracking extracts read, write, and edit tool calls from the messages being summarized. The compaction prompt includes these paths so the summary preserves awareness of which files were examined or modified:

<read-files>
src/main.rs
src/config.rs
</read-files>

<modified-files>
src/auth.rs
</modified-files>

Configurable parameters:

Parameter	Default	Purpose
`reserve_tokens`	8% of context window	Safety margin for response generation
`keep_recent_tokens`	10% of context window	Minimum recent context preserved

Compaction can also be triggered manually with /compact in interactive mode or the compact RPC command.

Multi-Provider Routing & Model Registry

Pi routes model requests through a provider factory that resolves the correct backend implementation from a (provider, model, api) tuple.

Resolution flow:

User specifies --provider openai --model gpt-4o
               │
               ▼
  ┌──────────────────────────┐
  │  Provider Metadata Table  │  Maps "openai" → canonical ID,
  │                           │  determines API type (Completions
  │                           │  vs Responses vs custom)
  └────────────┬──────────────┘
               │
  ┌────────────▼──────────────┐
  │  URL Normalization         │  Appends /chat/completions,
  │                            │  /responses, or /chat depending
  │                            │  on detected API type
  └────────────┬──────────────┘
               │
  ┌────────────▼──────────────┐
  │  Compat Config             │  Applies per-model overrides:
  │                            │  system_role_name, max_tokens
  │                            │  field name, feature flags
  └────────────┬──────────────┘
               │
  ┌────────────▼──────────────┐
  │  Provider Instance         │  Anthropic | OpenAI | Gemini
  │                            │  Cohere | Azure | Bedrock | ...
  └───────────────────────────┘

models.json overrides: Users can define custom providers in ~/.pi/agent/models.json or .pi/models.json. Each entry specifies a model ID, base URL, API type, and optional compat flags, letting you route to self-hosted models, proxies, or providers that Pi does not natively support.

Compat config handles the differences between OpenAI-compatible APIs:

Override	Example	Purpose
`system_role_name`	`"developer"`	o1 models use "developer" instead of "system"
`max_tokens_field`	`"max_completion_tokens"`	Some models require a different field name
`supports_tools`	`false`	Suppress tool definitions for models that reject them
`supports_streaming`	`false`	Fall back to non-streaming for incompatible endpoints
`custom_headers`	`{"X-Custom": "val"}`	Per-provider header injection

Fuzzy matching: When a provider name doesn't match any known provider, Pi computes edit distance against all registered names and suggests the closest match in the error message.

Extension Hostcall Protocol

Extensions run in an embedded QuickJS runtime (rquickjs crate) and communicate with Pi through a structured hostcall protocol. This is the mechanism that lets JavaScript code invoke Pi's built-in tools, make HTTP requests, and interact with the session, all without direct OS access.

Execution model:

┌─────────────────── QuickJS VM ───────────────────┐
│                                                   │
│  extension.js calls:                              │
│    pi.tool("read", {path: "src/main.rs"})         │
│      │                                            │
│      ▼                                            │
│    enqueue HostcallRequest {                      │
│      call_id: "hc-0042",                          │
│      kind: Tool { name: "read" },                 │
│      payload: { path: "src/main.rs" },            │
│    }                                              │
│      │                                            │
│      ▼                                            │
│    return Promise (resolve/reject stored in map)  │
│                                                   │
└────────────────────────┬──────────────────────────┘
                         │
    drain_hostcall_requests()
                         │
                         ▼
┌─────────────── ExtensionDispatcher ──────────────┐
│                                                   │
│  1. Check capability policy:                      │
│     read tool → requires "read" capability        │
│     → Policy says: Allow / Deny / Prompt          │
│                                                   │
│  2. If allowed → dispatch to ToolRegistry         │
│     → Execute read tool                           │
│     → Get ToolOutput                              │
│                                                   │
│  3. complete_hostcall("hc-0042", Ok(result))      │
│     → Resolves the Promise in QuickJS             │
│                                                   │
│  4. runtime.tick()                                │
│     → Drains Promise .then() chains               │
│     → Extension JS continues execution            │
│                                                   │
└───────────────────────────────────────────────────┘

Capability mapping: Each hostcall kind maps to a required capability:

Hostcall	Required Capability	Dangerous?
`pi.tool("read", ...)`	`read`	No
`pi.tool("write", ...)`	`write`	No
`pi.tool("bash", ...)`	`exec`	Yes
`pi.http(request)`	`http`	No
`pi.exec(cmd, args)`	`exec`	Yes
`pi.env(key)`	`env`	Yes
`pi.session(op, ...)`	`session`	No
`pi.ui(op, ...)`	`ui`	No
`pi.log(entry)`	`log`	No (always allowed)

Deduplication: Each hostcall's parameters are canonicalized (object keys sorted, structure normalized) and SHA-256 hashed. Identical requests within a short window can be deduplicated to avoid redundant tool executions.

Fast lane vs compatibility lane: Pi has two execution lanes for hostcalls:

Fast lane is used when the call shape matches known safe patterns (for example common tool and session operations). This avoids extra allocation and parsing work.
Compatibility lane is the fallback for uncommon or partially-specified calls.
Both lanes still enforce the same capability policy and permission checks.
Operators can force compatibility-lane routing globally or per extension as an emergency control path.

For observability, each call is tagged with a stable lane key (for example tool|tool.read|filesystem or tool|fallback|filesystem) so latency and failure trends can be grouped consistently.

Built-in consistency guard (shadow dual execution): Pi can sample a small subset of read-only hostcalls, execute them through both lanes, and compare canonical output fingerprints. If divergence crosses a configured budget, Pi automatically backs off the fast lane for a period. This gives performance wins without silently changing behavior.

Adaptive dispatch mode under load: Pi can switch between:

sequential_fast_path for simpler/low-contention workloads
interleaved_batching when contention and queue pressure rise

Mode changes are gated by sample coverage and risk checks, so Pi does not switch based on thin or cherry-picked evidence.

Runtime telemetry for debugging and tuning: Pi records structured hostcall telemetry (pi.ext.hostcall_telemetry.v1) with lane choice, fallback reason, dispatch latency share, marshalling path, and optimization hit/miss fields. This is used by perf reports and reliability diagnostics.

Auto-repair pipeline: When an extension fails to load or produces runtime errors, Pi's repair system can automatically fix common issues:

Repair Mode	Behavior
`Off`	No repairs
`Suggest`	Log suggestions, don't apply
`AutoSafe` (default)	Apply provably safe fixes (missing file paths, asset references)
`AutoStrict`	Apply aggressive heuristic fixes (pattern-based transforms)

Compatibility scanner: Before loading, Pi statically analyzes extension source code for imports, require() calls, and forbidden patterns (eval, Function(), process.binding, dlopen). The scan produces a capability evidence ledger that informs policy decisions.

Environment variable filtering: Extensions calling pi.env() hit a blocklist that denies access to API keys, credentials, tokens, and private keys. The filter blocks exact matches (ANTHROPIC_API_KEY, AWS_SECRET_ACCESS_KEY), suffix patterns (*_API_KEY, *_SECRET, *_TOKEN), and prefix patterns (AWS_SECRET_*, AWS_SESSION_*). Only PI_* variables are unconditionally allowed.

Trust lifecycle and kill switch: Extension trust state is tracked explicitly (pending, acknowledged, trusted, killed). A kill switch demotes an extension to killed, quarantines it in the runtime risk controller, emits a critical alert, and writes an audit record. Lifting the switch requires an explicit operator action and moves the extension back to acknowledged.

Extension Runtime Decision Logic (Plain English)

The extension runtime includes a few small decision engines so behavior stays stable as workload patterns change:

Value-of-information planner (VOI): Ranks candidate probes by "expected learning per millisecond" and picks the best set under a strict overhead budget. Stale or low-value candidates are skipped with explicit reasons.
Shard load controller: Adjusts routing weights, batch budgets, and backoff/help factors based on queue pressure, latency, and starvation risk. Damping and oscillation guards prevent overreaction.
Policy safety evaluator: Replays historical samples with multiple estimators and only approves a policy when sample support is strong, uncertainty is low, and predicted regret stays within limit.

These pieces are intentionally conservative: if confidence is weak, Pi holds steady instead of making an aggressive switch.

Interactive TUI Architecture

The interactive mode uses the Elm Architecture (Model-Update-View) via the charmed_rust library family, which is a Rust port of Go's Bubble Tea framework.

Component stack:

┌────────────────────────────────────────────────────┐
│                 Terminal (crossterm)                │
│  Raw mode │ Alt screen │ Keyboard/Mouse events      │
└──────────────────────┬─────────────────────────────┘
                       │
┌──────────────────────▼─────────────────────────────┐
│             bubbletea Program Loop                  │
│  Init() → Update(Msg) → View() → render cycle      │
└──────────────────────┬─────────────────────────────┘
                       │
┌──────────────────────▼─────────────────────────────┐
│                  PiApp (Model)                      │
│                                                     │
│  ┌─────────────┐ ┌──────────────┐ ┌─────────────┐  │
│  │  TextArea    │ │  Viewport    │ │  Spinner     │  │
│  │  (editor)    │ │  (convo)     │ │  (status)    │  │
│  └─────────────┘ └──────────────┘ └─────────────┘  │
│                                                     │
│  ┌─────────────────────────────────────────────┐    │
│  │           Overlay Stack                      │    │
│  │  Model Selector │ Session Picker │ /tree     │    │
│  │  Settings UI    │ Theme Picker   │ Branches  │    │
│  │  Capability Prompt (extension UI)            │    │
│  └─────────────────────────────────────────────┘    │
└──────────────────────┬─────────────────────────────┘
                       │
              async channels (mpsc)
                       │
┌──────────────────────▼─────────────────────────────┐
│             Agent Async Task                        │
│  Runs on asupersync runtime                         │
│  Streams provider responses                         │
│  Executes tools                                     │
│  Sends PiMsg events back to TUI thread              │
└────────────────────────────────────────────────────┘

The async/sync bridge: The agent runs on the asupersync async runtime in a separate thread. It communicates with the bubbletea UI thread through mpsc channels. Each streaming event (text delta, tool start, tool update, agent done) becomes a PiMsg variant delivered to PiApp::update(), keeping the UI responsive during API streaming and tool execution.

Viewport scrolling: The conversation viewport tracks whether the user is at the bottom. When new content arrives and the user hasn't scrolled up, the viewport auto-follows the stream tail. Scrolling up disables auto-follow; pressing End or typing a new message re-enables it.

Overlay system: Modal UIs (model selector, session picker, branch navigator, extension capability prompts) stack on top of the main conversation view. Each overlay captures keyboard input until dismissed. Only the topmost active overlay receives events.

Slash commands available in the interactive editor:

Command	Action
`/help`	Show available commands and keybindings
`/model` or `Ctrl+L`	Open model selector with fuzzy search
`Ctrl+P` / `Ctrl+Shift+P`	Cycle scoped models forward/backward
`/tree`	Browse and fork the conversation tree
`/clear`	Clear conversation and start fresh
`/compact`	Trigger manual compaction
`/thinking <level>`	Change thinking level mid-conversation
`/share`	Export session to GitHub Gist
`/exit` or `Ctrl+C`	Exit Pi

RPC Protocol

The RPC mode (pi --mode rpc) exposes a line-delimited JSON protocol over stdin/stdout for programmatic integration. Each line is a self-contained JSON object.

Client → Pi (stdin):

{"type": "prompt", "message": "Explain this function", "id": "req-001"}
{"type": "steer", "message": "Focus on error handling"}
{"type": "follow_up", "message": "Now add tests"}
{"type": "abort"}
{"type": "get_state"}
{"type": "compact", "reserveTokens": 8192, "keepRecentTokens": 20000}

Pi → Client (stdout):

{"type": "agent_start", "sessionId": "..."}
{"type": "message_update", "message": {...}, "assistantMessageEvent": {"type": "text_delta", "delta": "The function", "contentIndex": 0}}
{"type": "tool_execution_start", "toolCallId": "...", "toolName": "read", "args": {}}
{"type": "tool_execution_end", "toolCallId": "...", "toolName": "read", "result": {}, "isError": false}
{"type": "agent_end", "sessionId": "...", "messages": [...]}
{"type": "response", "id": "req-001", "command": "prompt", "success": true, "data": {"status": "ok"}}

I/O architecture: Two dedicated threads handle stdin reading and stdout writing, bridged to the async agent runtime via channels. The stdin thread retries on transient errors to prevent dropped input. The stdout thread flushes after every line to prevent buffering delays.

Message queuing: While the agent is streaming a response, incoming messages are routed to one of two queues:

Queue	Behavior	Use Case
Steering	Interrupts current response; processed on next turn	Course corrections
Follow-up	Queued until current response completes	Sequential instructions

Queue modes (All or OneAtATime) control whether multiple queued messages are batched into a single turn or processed individually.

Extension UI over RPC: When an extension requests user input (capability prompt, selection dialog), Pi emits an extension_ui_request event. The client renders the prompt in its own UI and responds with an extension_ui_response message. IDE extensions can then present native UI for capability decisions instead of falling back to terminal prompts.

Session Indexing

Session resume (pi -c or pi -r) needs to find the most recent session for the current project without scanning every JSONL file on disk. Pi maintains a SQLite index (session-index.sqlite) that provides constant-time lookups.

Schema:

CREATE TABLE sessions (
    path            TEXT PRIMARY KEY,
    id              TEXT NOT NULL,
    cwd             TEXT NOT NULL,
    timestamp       TEXT NOT NULL,
    message_count   INTEGER NOT NULL,
    last_modified   INTEGER NOT NULL,
    size_bytes      INTEGER NOT NULL,
    name            TEXT
);

Update lifecycle:

After saving a session JSONL file, Pi upserts its metadata into the index
pi -c queries WHERE cwd = ? ORDER BY last_modified DESC LIMIT 1
pi -r queries the same table and presents a picker sorted by recency

Concurrency: A file-based lock (session-index.lock) serializes writes from concurrent Pi instances. Reads use WAL mode for non-blocking access.

Staleness-based reindexing: If the index is older than a configurable threshold, Pi runs a full re-scan of the sessions directory to catch files created by other instances or manual edits. The re-scan keeps the index accurate without a centralized daemon.

Session Store V2 Sidecar (Large Session Fast-Path)

Pi also supports a v2 sidecar store next to JSONL sessions for faster resume and stronger corruption checks on long histories.

What it adds:

Segmented append log files (instead of one ever-growing JSONL file)
Offset index rows for direct seeks and fast tail reads
Periodic checkpoints and a manifest snapshot
Migration ledger entries for auditability
Checkpoint-based rollback path with explicit rollback event logging

How resume works:

If a v2 sidecar exists and is fresh, Pi opens from the sidecar index + segments.
If sidecar data is stale relative to the source JSONL, Pi falls back to JSONL parsing.
If index data is missing/corrupt but segments are valid, Pi rebuilds the index.

Integrity strategy:

Segment frames carry payload and chain hashes.
Index rows store byte offsets plus CRC32C checksums.
Validation checks offset bounds, checksum matches, and frame/index alignment before trusting the sidecar.
Truncated trailing frames are recoverable during rebuild; non-EOF frame corruption fails closed instead of silently dropping data.

CLI support:

pi migrate <path> --dry-run validates migration without writing.
pi migrate <path> performs JSONL-to-v2 migration and verifies parity.

Authentication & Credential Management

Beyond simple API keys, Pi supports OAuth, AWS credential chains, service key exchange, and bearer-token auth. Credentials are stored in ~/.pi/agent/auth.json with file-locked access to prevent corruption from concurrent instances. Stored API keys can be literal strings, $ENV:VAR_NAME references, or $CMD:shell command / $COMMAND:shell command sources that resolve trimmed stdout at request time.

Mechanism	Providers	Details
API Key	Anthropic, OpenAI, Gemini, Cohere, and many OpenAI-compatible providers	Static key via env var or settings
OAuth	Anthropic, OpenAI Codex, Google Gemini CLI, Google Antigravity, Kimi for Coding, GitHub Copilot, GitLab, and extension-defined OAuth providers	PKCE/state-validated flow with automatic refresh; Kimi uses device flow
AWS Credentials	Bedrock	Access key + secret + optional session token; region-aware
Service Key	SAP AI Core	Client ID/secret exchange for bearer token
Bearer Token	Custom providers	Static token in auth storage

OAuth token lifecycle:

User runs pi with an OAuth-configured provider
Pi checks auth.json for an existing token
If missing: opens browser to authorization URL, user authenticates, Pi receives authorization code, exchanges it for access + refresh tokens, stores both with expiry timestamp
If expired but refresh token valid: exchanges refresh token for new access token, updates auth.json
Bearer token attached to API requests

Google CLI-style OAuth providers carry project metadata with the token payload. Pi preserves and refreshes that payload and can resolve project IDs from GOOGLE_CLOUD_PROJECT or local gcloud config when needed.

Credential status reporting: pi config shows the status of each configured provider's credentials: Missing, ApiKey, OAuthValid (with time until expiry), OAuthExpired (with time since expiry), AwsCredentials, or BearerToken.

Diagnostic codes: Auth failures produce specific diagnostic codes (MissingApiKey, InvalidApiKey, QuotaExceeded, OAuthTokenRefreshFailed, MissingAzureDeployment, MissingRegion, etc.) with context-specific error hints rather than generic messages.

Tool Details

read

Read file contents (optionally images):

Input: { "path": "src/main.rs", "offset": 10, "limit": 50 }

Supports images (jpg, png, gif, webp) with optional auto-resize
Streams file bytes in chunks with hard size limits to reduce peak memory usage
Applies defensive image decode limits to block decompression-bomb/OOM inputs
Truncates at 2000 lines or 1MB
Returns continuation hint if truncated

bash

Execute shell commands with timeout and output capture:

Input: { "command": "cargo test", "timeout": 120 }

Default 120s timeout, configurable per-call
Set timeout: 0 to disable the default timeout
Process tree cleanup on timeout (kills children)
Rolling buffer for real-time output
Full output saved to temp file if truncated

edit

Surgical string replacement:

Input: { "path": "src/lib.rs", "old": "fn foo()", "new": "fn bar()" }

Exact string matching (no regex)
Fails if old string not found or ambiguous
Returns diff preview

grep

Search file contents:

Input: { "pattern": "TODO", "path": "src/", "context": 2, "limit": 100 }

Regex patterns supported
Context lines before/after matches
Respects .gitignore

find

Discover files by pattern:

Input: { "pattern": "*.rs", "path": "src/", "limit": 1000 }

Glob patterns via fd
Sorted by modification time
Respects .gitignore

ls

List directory contents:

Input: { "path": "src/", "limit": 500 }

Alphabetically sorted
Directories marked with trailing /
Truncates at limit

Performance Engineering

Why Rust Matters for CLI Tools

CLI tools have different performance requirements than servers or GUI applications. The critical metric is time-to-first-interaction: how quickly can the user start typing after invoking the command?

Phase	TypeScript/Node.js	Rust
Process spawn	~10ms	~10ms
Runtime initialization	200-500ms	0ms (no runtime)
Module loading	100-300ms	0ms (static linking)
JIT warmup	50-100ms	0ms (AOT compiled)
Total	360-910ms	~10ms

This difference compounds with usage frequency, especially in short iterative terminal workflows.

Extreme Optimization Playbook

Pi is optimized more like a low-latency engine than a typical CLI app. We intentionally apply aggressive optimization at multiple layers, not just "compile with --release and hope."

Where the speed comes from:

Startup path kept minimal: no JS runtime bootstrap, no module graph loading, no JIT warmup.
Hot hostcall specialization: common extension hostcalls use typed fast paths; uncommon shapes fall back to compatibility paths.
Adaptive dispatch under load: hostcall scheduling can switch modes when contention rises, then switch back when pressure drops.
Fast-path safety guardrails: sampled shadow dual-execution checks ensure optimizations do not silently change behavior.
Low-allocation rendering: TUI render buffers and markdown render results are cached/reused instead of rebuilt every frame.
Fast resume internals: session indexing plus the v2 sidecar layout avoid expensive full-history scans on resume.
Bounded growth controls: compaction and truncation keep token/context growth and tool-output payload growth from degrading responsiveness over long sessions.
Measurement-first culture: perf artifacts are schema-validated and claim-gated in CI, so optimization work is driven by evidence and regressions are caught early.

This is why Pi can stay responsive even with heavy streaming, tool usage, large session histories, and extension workloads running at the same time.

Optimization Catalog (Code + Commit History)

This catalog reflects a long sequence of changes across runtime, storage, streaming, and UI.

Concrete engineering work in this codebase includes:

Area	What we built	Why it matters
Extension dispatch core	Typed hostcall opcode fast paths, compatibility fallback lane, zero-copy payload arena, canonical-hash shortcuts, interned operation paths	Cuts per-call overhead on the hottest extension operations while preserving correctness fallback paths
Registry/policy lookup	Immutable policy snapshots with O(1) capability checks, plus RCU-style metadata snapshots for extension registry/tool metadata	Removes repeated dynamic lookup overhead in hot authorization/dispatch paths
Queueing + concurrency	Core-pinned SPSC reactor mesh, S3-FIFO-inspired admission with fairness guards, BRAVO-style fallback behavior	Improves tail latency under contention instead of only optimizing median latency
Batched execution	AMAC-style interleaved batch executor with stall-aware toggling	Avoids head-of-line stalls when many independent hostcalls are in flight
IO specialization	io_uring lane policy + telemetry and compatibility fallback	Routes IO-heavy calls to a specialized lane when safe and beneficial
Runtime startup for extensions	QuickJS pre-warm path, warm isolate/bytecode cache behavior, and startup pipeline parallelization	Lowers cold-start overhead before the first real extension workload
JS bridge/scheduler path	Pending-job fast-path tuning and bridge-level dispatch cleanup in hot extension loops	Reduces overhead between JS requests and Rust execution
Adaptive control loops	Regime-shift detection (CUSUM/BOCPD), budget controllers, VOI-based experiment planner, mean-field load controller, off-policy evaluation gates	Lets runtime behavior adapt to workload shifts without blind tuning
Fast-path safety	Shadow dual-execution sampling with automatic rollback/backoff on divergence	Prevents speed work from silently changing semantics
Trace-level optimization	Hostcall superinstruction compiler + tier-2 trace-JIT path	Fuses repeated opcode traces and lowers repeated dispatch overhead
Tool execution strategy	Dynamic read-only tool classification + parallel tool execution paths	Increases throughput when multiple tool calls can safely run together
Session write path	Write-behind autosave queue, durability modes, incremental append, checkpointed rewrite strategy, single-buffer append serialization	Keeps interaction fast while still supporting stronger durability when needed
Session index path	Async coalesced index updates, pending-drain hot-path tuning, and reduced allocation/boxing overhead	Keeps resume/discovery metadata updates off the interactive hot path
Session resume path	Session Store V2 sidecar (segmented log + offset index), O(index+tail) open path, stale-sidecar detection, migration/rollback tooling	Avoids full-file rescans on large histories and improves recovery behavior
Long-session maintenance	Background compaction/snapshot workers with quotas + lazy hydration paths	Controls session growth and keeps long-running workspaces responsive
Compaction internals	Binary-search cut-point logic, serialization helper extraction, and zero-allocation-oriented cleanup on compaction paths	Lowers compaction overhead and keeps compaction from becoming a pause source
Streaming internals	SSE parser event-type interning, scanned-byte tracking (`scanned_len`), UTF-8 recovery hardening	Reduces repeated scanning/allocation during token streaming and improves resilience
Provider/message memory path	Zero-copy request context migration (`Cow`), `Arc`-based message/result sharing, clone elimination in stream end paths	Removes hot-path cloning and allocation churn in core agent/provider loops
TUI rendering path	Message render cache, conversation-prefix cache, reusable render buffers, viewport/render-path refactors, Criterion perf gates	Reduces redraw cost and jitter while streaming long outputs
Startup/resource loading	Parallelized skill/prompt/theme loading plus precomputed tool definitions/command names	Moves heavy initialization off the critical path to improve time-to-interaction
Allocator/build profile	jemalloc default for allocation-heavy paths, speed-oriented release profile, strict artifact validation for perf claims	Improves runtime consistency and prevents benchmark/reporting drift
Perf governance	Scenario matrix, claim-integrity gates, strict no-data fail behavior, variance/confidence artifacts, reproducible orchestration bundles	Makes performance claims auditable and regression detection automatic
Hostcall marshalling planner	`HostcallRewriteEngine` uses a small cost model to pick fast opcode fusion only when it is clearly cheaper and unambiguous; otherwise it stays on the canonical path and records fallback reason	Gains speed on hot marshalling shapes without risking silent semantic drift from ambiguous rewrites
Tool text-processing hot path	`truncate_head`/`truncate_tail` use lazy line traversal and `memchr` line counting; normalization switched to a single-pass transform instead of chained string rewrites	Large file/tool outputs avoid unnecessary intermediate allocations and stay responsive
JS bridge regex and parser micro-paths	Frequent regex checks in the extension JS bridge are `OnceLock`-cached; hot bridge calls avoid repeated setup work	Cuts repeated per-call overhead in extension-heavy sessions
CLI/autocomplete process-spawn reduction	`fd`/`rg` availability checks are cached, and autocomplete file-index refresh runs in background with stale-update dropping	Keeps completion and command handling quick even in very large repositories
Session identity/index micro-optimizations	O(1) entry-id cache, single-pass metadata finalization, and append-path cleanups replace multi-pass/copy-heavy behavior	Reduces overhead on append/save/rebuild when sessions become large
Benchmark-driven rollback discipline	Candidate micro-optimizations are benchmarked and can be reverted when real workloads regress (for example, a newline-scan `memchr` swap in SSE was rolled back)	Prevents "optimizations" that look fast in theory but slow down real usage

Optimization spans algorithms, execution lanes, memory movement, queue discipline, storage layout, and validation policy as one system.

Release Profile and Binary Size Gate

The shipping release profile is tuned for runtime speed:

[profile.release]
opt-level = 3        # Maximum speed optimization
lto = true           # Link-time optimization across all crates
codegen-units = 1    # Single codegen unit (slower compile, better optimization)
panic = "abort"      # No unwinding machinery
strip = true         # Remove symbol tables

Binary size is explicitly budgeted in CI via binary_size_release, with a target threshold of 22.0 MB. However, current builds with default features (including wasm-host, image-resize, jemalloc) produce ~44MB binaries. This discrepancy represents a known issue where default features have grown beyond the original size budget.

Benchmark Evidence vs Shipping Artifacts

Pi separates performance evidence artifacts from distributable release artifacts:

Benchmark evidence artifacts (PERF-3X and certification inputs) are produced by scripts/perf/orchestrate.sh and scripts/bench_extension_workloads.sh, and must carry run provenance (correlation_id) plus profile labels (for example build_profile=perf).
Shipping artifacts (end-user binaries) are built with Cargo release profile and distributed via GitHub Releases + installer paths.

Policy implication: release/size artifacts alone are not valid evidence for global performance claims. Performance claims must cite benchmark evidence bundles with reproducible provenance. See docs/testing-policy.md and docs/releasing.md for normative policy details.

Latest full performance orchestrator checkpoint (2026-04-23):

Run output: tests/perf/reports/ (budget_summary.json, PERF_BUDGETS.md)
Correlation ID: 20260423T002033Z-perf-refresh
Summary: All CI-enforced performance budgets within thresholds
Measured startup guards: --version P95 under 100ms budget threshold (from tests/perf/reports/budget_summary.json)

Latest certification/evidence refresh (2026-05-01):

Unified evidence bundle: 28/28 sections present, 11/11 required sections present, 0 missing, 0 invalid (from tests/evidence_bundle/index.json)
Full-suite gate: 20/20 gates passed, including 14/14 blocking gates (from tests/full_suite_gate/full_suite_verdict.json)
Drop-in certification: 20/20 certification gates passed, overall verdict CERTIFIED (from docs/evidence/dropin-certification-verdict.json)
Extension must-pass gate: 123/123 must-pass extensions passed; stretch set 98/101 passed (from tests/ext_conformance/reports/gate/must_pass_gate_verdict.json)

Fast Loop vs Definitive Benchmarks

For day-to-day implementation, use targeted checks to keep iteration fast. Reserve definitive benchmark conclusions for integration boundaries where full evidence is regenerated.

Fast loop (non-authoritative): file-scoped cargo fmt --check and targeted test replays (rch exec -- cargo test --test ... when compilation is non-trivial).
Definitive pass (authoritative): offload heavy runs with strict remote gating (rch exec -- ... or script wrappers with --require-rch), then require updated evidence artifacts:
- tests/perf/reports/phase1_matrix_validation.json
- tests/full_suite_gate/full_suite_verdict.json
- tests/full_suite_gate/certification_verdict.json
- tests/full_suite_gate/extension_remediation_backlog.json

This keeps inner loops responsive while preserving strict claim-integrity at release time.

Extension Workload Hotspot Profiling

Pi includes a dedicated workload harness for extension runtime bottlenecks:

cargo run --example ext_workloads -- \
  --out artifacts/perf/ext_workloads.jsonl \
  --matrix-out artifacts/perf/ext_hostcall_hotspot_matrix.json \
  --trace-out artifacts/perf/ext_hostcall_bridge_trace.jsonl

This harness does more than raw timing:

Breaks hostcall cost into six stages: marshal, queue, schedule, policy, execute, io
Produces a hotspot matrix (pi.ext.hostcall_hotspot_matrix.v1) for quick bottleneck ranking
Produces bridge trace events (pi.ext.hostcall_trace.v1) for per-call debugging
Measures how stage pairs interact and verifies full stage-pair coverage
Generates a VOI scheduler plan (pi.ext.voi_scheduler.v1) to recommend the next highest-value experiments under a fixed overhead budget

In plain terms: it helps answer "what should we optimize next?" with data, not guesswork.

Claim-Integrity Gates for Performance Reporting

Pi's perf pipeline includes strict evidence checks so global speed claims cannot be based on partial or stale data.

scripts/perf/orchestrate.sh generates artifacts tied to a shared correlation_id for the same run.
scripts/e2e/run_all.sh validates required schemas, freshness, and correlation_id alignment before considering claims valid.
tests/release_evidence_gate.rs fails closed when conformance/perf artifacts are missing run_id or correlation_id, or when lineage fields disagree across linked artifacts.
scripts/e2e/run_all.sh emits an evidence-adjudication matrix and only treats evidence as canonical when freshness and lineage checks both pass.
Key release-facing artifacts include:
- pi.perf.extension_benchmark_stratification.v1
- pi.perf.phase1_matrix_validation.v1
- pi.claim_integrity.evidence_adjudication_matrix.v1

If the evidence set is incomplete or contradictory, the claim-integrity gate stays closed and reports exactly why.

Allocator Strategy for Benchmarks

Default Linux/macOS builds use jemalloc for allocation-heavy paths. FreeBSD and MSVC builds always use the platform allocator; FreeBSD libc already uses jemalloc internally, and mixing allocator domains across libc/pthread and C dependencies can turn heap corruption into thread-spawn crashes. For allocator experiments, Pi supports explicit system and jemalloc benchmark variants:

# System allocator baseline + jemalloc variant in one repeatable run
BENCH_ALLOCATORS_CSV=system,jemalloc \
  ./scripts/bench_extension_workloads.sh

The benchmark harness records both requested and effective allocator metadata in its JSONL output (allocator_requested, allocator_effective, allocator_fallback_reason) via PI_BENCH_ALLOCATOR.

system: build with the normal benchmark feature set except jemalloc
jemalloc: build with --features jemalloc where supported by the target
auto: prefer jemalloc, fall back to system if build fails

If jemalloc is requested but unavailable for the current build, the run fails closed to the compiled allocator and includes a fallback reason in artifacts.

Memory Usage

Rust's ownership model enables predictable memory usage without garbage collection pauses:

State	Memory
Startup (idle)	~15MB
Active session (small)	~25MB
Large file in context	~30-50MB
Streaming response	+0MB (streamed, not buffered)

The absence of a GC means no surprise latency spikes during streaming output.

Streaming Architecture

Responses stream token-by-token from the API to the terminal with minimal buffering:

API Server → TCP → SSE Parser → Event Handler → Terminal
     │                              │
     └──────── no buffering ────────┘

Each token appears on screen within milliseconds of leaving Anthropic's servers. The SSE parser processes events as they arrive rather than waiting for complete responses.

TUI Rendering Performance

The interactive TUI targets 60fps rendering with several optimization layers:

Frame timing telemetry: Every render cycle is instrumented. Slow frames (>16ms) are tracked and classifiable by phase: viewport sync, message encoding, markdown rendering. This data feeds the internal performance monitor.

Message render cache: Markdown-to-ANSI conversion involves syntax highlighting, table layout, and link detection. Pi caches the rendered output per message and invalidates only on theme change or terminal resize. During streaming, only the actively-changing message is re-rendered; all prior messages hit the cache.

Pre-allocated render buffers: The RenderBuffers struct is reused across render cycles. Rather than allocating new String buffers each frame, Pi writes into pre-sized buffers and clears them before reuse, eliminating thousands of small allocations per second during streaming.

Memory pressure monitoring: A MemoryMonitor samples process heap size and classifies it into three tiers:

Tier	Threshold	Action
Normal	<80% of budget	No action
Pressure	80-95% of budget	Collapse tool output displays, hide thinking blocks
Critical	>95% of budget	Truncate older messages, force compaction

Progressive degradation keeps Pi responsive during long sessions with accumulated tool output.

Troubleshooting

For a more complete guide, see docs/troubleshooting.md.

"fd not found"

The find tool requires fd:

# Ubuntu/Debian
apt install fd-find

# macOS
brew install fd

# The binary might be named fdfind
ln -s $(which fdfind) ~/.local/bin/fd

"API key not set"

export ANTHROPIC_API_KEY="sk-ant-..."

# Or in settings.json
{ "apiKey": "sk-ant-..." }

# Or per-command
pi --api-key "sk-ant-..." "Hello"

"Session corrupted"

Sessions are append-only JSONL. If corruption occurs:

# Start fresh
pi --no-session

# Or delete the problematic session
rm ~/.pi/agent/sessions/--home-user-project--/corrupted-session.jsonl

"Streaming hangs"

Check your network connection. Pi uses SSE which requires stable connections:

# Test with curl
curl -N https://api.anthropic.com/v1/messages

"Tool output truncated"

This is intentional to prevent context overflow. Use offset/limit:

# In the conversation
"Read lines 2000-4000 of that file"

Limitations

Pi is honest about what it doesn't do:

Limitation	Workaround
Not all provider APIs	Built-in support is backed by 10 native provider implementation modules: Anthropic, OpenAI Chat, OpenAI Responses/Codex Responses, Gemini, Cohere, Azure OpenAI, Bedrock, Vertex AI, GitHub Copilot, and GitLab Duo; some ecosystem-specific APIs are still TBD
No web browsing	Use bash with curl
No GUI	Terminal-only by design
Some extensions need npm stubs	Common stubs are provided; unlisted npm packages still require a stub. See docs/planning/EXTENSIONS.md §8.1
English-centric	Works but not optimized for other languages
Nightly Rust required	Uses 2024 edition features

Design Philosophy

Specification-First Porting

This port follows a "specification extraction" methodology rather than line-by-line translation:

Extract behavior: Study the TypeScript implementation to understand what it does, not how
Document the spec: Write down expected behaviors, edge cases, and invariants
Implement from spec: Write idiomatic Rust that satisfies the spec
Conformance testing: Verify behavior matches via fixture-based tests

This approach yields better code than mechanical translation. TypeScript idioms (callbacks, promises, class hierarchies) don't map cleanly to Rust (ownership, traits, enums). Fighting the language produces worse results than embracing it.

Conformance Testing

The test suite includes fixture-based conformance tests that validate tool behavior:

{
  "version": "1.0",
  "tool": "edit",
  "cases": [
    {
      "name": "edit_simple_replace",
      "setup": [
        {"type": "create_file", "path": "test.txt", "content": "Hello, World!"}
      ],
      "input": {
        "path": "test.txt",
        "oldText": "World",
        "newText": "Rust"
      },
      "expected": {
        "content_contains": ["Successfully replaced"],
        "details": {"oldLength": 5, "newLength": 4}
      }
    }
  ]
}

Each fixture specifies:

Setup: Files/directories to create before the test
Input: Tool parameters
Expected: Output content patterns, exact field matches, or error conditions

The Rust implementation can be validated against the TypeScript original without coupling to implementation details.

Extension System

Pi supports legacy JS/TS extensions via an embedded QuickJS runtime. Unlike traditional plugin systems, extensions run in a sandboxed, capability-gated environment with no ambient OS access:

No Node/Bun required: QuickJS + Pi-provided shims for common Node APIs
Capability-based security: each host connector call is policy-checked and logged
Conformance-tested: status is tracked in docs/ext-compat.md and tests/ext_conformance/reports/pipeline/
Sub-100ms load times: extensions load in <100ms (P95) with no JIT warmup

Legacy extension behavior is automatic:

Existing .js/.ts extensions run directly (no manual conversion step).
*.native.json descriptors are optional and mainly useful for native-rust runtime workflows.
One session currently uses one runtime family at a time (JS/TS or native descriptor).

Policy preset quick-start:

# Inspect current effective policy
pi --explain-extension-policy

# Switch profile for one command (safe | balanced | permissive)
pi --extension-policy balanced --explain-extension-policy

# Legacy alias is still accepted:
pi --extension-policy standard --explain-extension-policy

# Narrow dangerous-capability opt-in (preferred over permissive)
PI_EXTENSION_ALLOW_DANGEROUS=1 pi --extension-policy balanced --explain-extension-policy

Operator rollout playbook (compatibility-first local defaults + explicit lock-down):

# 1) Baseline: verify defaults are compatibility-first (`permissive`)
pi --explain-extension-policy

# 2) Staging: use balanced prompting, dangerous caps still denied by default
pi --extension-policy balanced --explain-extension-policy

# 3) Explicit lock-down for strict local/CI runs
pi --extension-policy safe --explain-extension-policy

# 4) Narrow opt-in for dangerous capabilities (preferred path)
PI_EXTENSION_ALLOW_DANGEROUS=1 pi --extension-policy balanced --explain-extension-policy

# 5) Explicit permissive mode when you want to be unambiguous
pi --extension-policy permissive --explain-extension-policy

settings.json baseline for local/dev:

{
  "extensionPolicy": {
    "defaultPermissive": true
  }
}

Use this to restore the stricter fallback without CLI flags:

{
  "extensionPolicy": {
    "defaultPermissive": false
  }
}

Interactive TUI: open /settings and toggle extensionPolicy.defaultPermissive.

CI guidance:

# CI default: keep dangerous capabilities disabled
pi --extension-policy safe --explain-extension-policy

# CI opt-in job (only where required), keep explicit and auditable
PI_EXTENSION_ALLOW_DANGEROUS=1 pi --extension-policy balanced --explain-extension-policy

Rollback rule: remove PI_EXTENSION_ALLOW_DANGEROUS, set extensionPolicy.profile back to safe or set extensionPolicy.defaultPermissive to false, and re-run pi --explain-extension-policy to confirm deny decisions.

See EXTENSIONS.md for the full architecture, runtime contract, and conformance results.

Unsafe Forbidden

The #![forbid(unsafe_code)] directive is project-wide and non-negotiable. Rationale:

Attack surface: Pi executes user-provided shell commands and reads arbitrary files
Memory bugs = security bugs: Buffer overflows or use-after-free in this context could be exploitable
Performance irrelevant: The bottleneck is network latency to the API, not CPU cycles
Dependencies audited: All dependencies either use no unsafe or are well-audited (e.g., rustls)

The safe Rust subset provides all necessary functionality without compromising security.

FAQ

Q: What's the relationship to the original Pi Agent? A: This is an authorized Rust port of Pi Agent by Mario Zechner, created with his blessing. The architecture differs significantly from the TypeScript original: it uses asupersync for structured concurrency and rich_rust (a port of Will McGugan's Rich library) for terminal rendering. The goal is idiomatic Rust while preserving Pi Agent's UX.

Q: Why rewrite in Rust? A: Startup time matters when you're in a terminal all day. Rust gives us <100ms startup vs 500ms+ for Node.js. Plus, no runtime dependencies to manage.

Q: Can I use providers beyond Anthropic (OpenAI/Gemini/Cohere/Azure/Bedrock/Vertex/Copilot/GitLab/Codex)? A: Yes. Pi has 10 native provider implementation modules: Anthropic, OpenAI Chat, OpenAI Responses/Codex Responses, Gemini (native + Gemini CLI + Antigravity routes), Cohere, Azure OpenAI, Amazon Bedrock, Vertex AI, GitHub Copilot, and GitLab Duo. Pi also supports many OpenAI-compatible presets (for example Groq, OpenRouter, Mistral, Together, DeepSeek, Cerebras, DeepInfra, Alibaba/Qwen, and Moonshot/Kimi). Provider IDs and aliases are case-insensitive. Set credentials and choose via --provider/--model; run pi --list-providers to see canonical IDs, aliases, and env keys.

Q: How do sessions work? A: By default, each session is a JSONL v3 file with message entries, parent references for branching, and compaction metadata. Builds include sqlite-sessions support by default, so configured deployments can use SQLite-backed session storage too; JSONL remains the default store unless configuration selects SQLite.

Q: Why is unsafe forbidden? A: Memory safety is non-negotiable for a tool that executes arbitrary commands. The performance cost is negligible for this use case.

Q: How do I extend Pi? A: Pi has a full extension system with two runtime families: JS/TS entrypoints run in embedded QuickJS, and *.native.json descriptors run in the native-rust descriptor runtime. Both are capability-gated and audited through the same policy system. One session uses one runtime family at a time. Extensions can register tools, slash commands, event hooks, flags, and custom providers. See EXTENSIONS.md for details. For built-in tool changes, implement the Tool trait in src/tools.rs.

Q: Why isn't X feature included? A: Pi focuses on core coding assistance. Features like web browsing, image generation, etc. are out of scope. Use specialized tools for those.

Q: How does compaction work? A: When a conversation exceeds the model's context window, Pi summarizes older messages using the LLM itself, storing the summary as a session entry. Recent messages are kept verbatim. The cut point is chosen at a turn boundary, and the summary includes a record of which files were read or modified so the model retains that awareness. Compaction runs automatically after each agent turn when needed, or manually via /compact.

Q: Can I add a custom provider that Pi doesn't support natively? A: Yes. Create a models.json file in ~/.pi/agent/ or .pi/ with entries specifying the model ID, base URL, and API type (usually openai-completions for OpenAI-compatible endpoints). Pi's compat config system handles field name differences and feature flag overrides. Extensions can also register entirely custom providers.

Q: How does Pi decide which session to resume? A: Pi maintains a SQLite session metadata index sidecar with WAL/lock handling and stale-index reindexing. When you run pi -c, it queries that index for the most recently modified session whose working directory matches your current project, including JSONL sessions and configured SQLite-backed sessions. This avoids scanning the filesystem on every resume.

Q: What happens if an extension tries to access something dangerous? A: Every hostcall from an extension is checked against the active capability policy before execution. Dangerous capabilities (exec, env) are denied by default under safe and balanced unless explicitly opted in (for example via PI_EXTENSION_ALLOW_DANGEROUS=1), and are available under permissive. For exec, Pi then applies command mediation before spawn: it classifies command+arg signatures and blocks critical classes by default (for example recursive delete, disk/device write, reverse shell), with strict/safe policy able to block high-tier classes as well (for example shutdown, process-kill, credential-file modification). Denied calls return errors to the extension Promise path, and denial events are recorded in redacted security-alert and exec-mediation audit artifacts. Sensitive env keys (API keys/tokens/secrets) remain filtered. If behavior escalates, you can kill-switch that extension into quarantined killed state immediately or force compatibility-lane routing as a containment step while investigating.

Q: Does Pi work with self-hosted or proxied LLMs? A: Yes. Point any provider at a custom base URL via models.json. Pi normalizes URL paths per API type and applies compatibility overrides for field-name and feature differences. This works with vLLM, Ollama, LiteLLM, and similar OpenAI-compatible servers.

Comparison

Feature	Pi	Claude Code	Aider	Cursor
Language	Rust	TypeScript	Python	Electron
Startup	<100ms	~1s	~2s	~5s
Memory	<50MB	~200MB	~150MB	~500MB
Providers	10 native provider implementation modules + OpenAI-compatible presets	Anthropic	Many	Many
Tools	8 built-in	Many	File-focused	IDE-integrated
Sessions	JSONL tree	Proprietary	Git-based	Proprietary
Open source	Yes	Yes	Yes	No

Development

Building

./scripts/cargo_headroom.sh build           # Debug build (remote offload)
./scripts/cargo_headroom.sh build --release # Release build (optimized, remote offload)
./scripts/cargo_headroom.sh test --all-targets # Full test run with disk preflight
# Lint checks (remote-safe split to avoid rch clippy timeout fail-open)
./scripts/cargo_headroom.sh clippy --lib --bins -- -D warnings
./scripts/cargo_headroom.sh clippy --tests -- -D warnings
./scripts/cargo_headroom.sh clippy --benches -- -D warnings
./scripts/cargo_headroom.sh clippy --examples -- -D warnings

When those variables are unset, cargo_headroom.sh defaults CARGO_TARGET_DIR and TMPDIR to a per-agent directory under /data/tmp/pi_agent_rust_cargo/..., writes a CACHEDIR.TAG, rejects accidental repo-root target directories, and fails before compilation if the target or temp mount has insufficient free space. Set PI_CARGO_RUNNER=local for a local-only run, PI_CARGO_BUILD_ROOT=<dir> for a different large volume, or PI_CARGO_HEADROOM_MIN_FREE_MB=<mb> for smaller focused checks.

Cargo Feature Defaults

Default builds enable image-resize, jemalloc, clipboard, wasm-host, and sqlite-sessions. The sqlite-sessions feature is therefore on for normal cargo build, cargo test, release, and installer builds; JSONL remains the default session store unless configuration selects SQLite storage. To build without SQLite session backend support, use --no-default-features and explicitly re-enable the feature subset you need, for example:

./scripts/cargo_headroom.sh build --no-default-features --features image-resize,clipboard

Testing

# Unified verification runner (recommended for deterministic evidence artifacts)
./scripts/e2e/run_all.sh --profile focused
./scripts/e2e/run_all.sh --profile ci
./scripts/e2e/run_all.sh --rerun-from tests/e2e_results/<timestamp>/summary.json --skip-unit

# Fast smoke/extension quality wrappers with strict remote enforcement
./scripts/smoke.sh --require-rch
./scripts/ext_quality_pipeline.sh --require-rch

# Multi-agent safety: with CODEX_THREAD_ID set, run_all defaults
# CARGO_TARGET_DIR to target/agents/<CODEX_THREAD_ID> unless overridden.
# Set CARGO_TARGET_DIR explicitly if you want a custom shared or isolated target.

# All tests
./scripts/cargo_headroom.sh test --all-targets

# Specific module
./scripts/cargo_headroom.sh test tools::tests
./scripts/cargo_headroom.sh test sse::tests

# Conformance tests
./scripts/cargo_headroom.sh test conformance

Focused validation tools:

# Dev-firstset gate before release build
rch exec -- cargo build --bin pi --bin ext_release_binary_e2e
PI_HTTP_REQUEST_TIMEOUT_SECS=0 rch exec -- \
  cargo run --example ext_release_binary_e2e -- \
  --pi-bin target/debug/pi \
  --provider ollama --model qwen2.5:0.5b \
  --jobs 10 --timeout-secs 600 --max-cases 20 --extension-policy balanced

# Full optimized release-binary run after gate passes
rch exec -- cargo build --release --bin pi --bin ext_release_binary_e2e
PI_HTTP_REQUEST_TIMEOUT_SECS=0 target/release/ext_release_binary_e2e \
  --pi-bin target/release/pi \
  --provider ollama --model qwen2.5:0.5b \
  --jobs 10 --timeout-secs 600 --extension-policy balanced

# Runtime risk ledger forensics (verify, replay, calibrate)
rch exec -- cargo run --example ext_runtime_risk_ledger -- verify --input path/to/runtime_risk_ledger.json
rch exec -- cargo run --example ext_runtime_risk_ledger -- replay --input path/to/runtime_risk_ledger.json
rch exec -- cargo run --example ext_runtime_risk_ledger -- calibrate --input path/to/runtime_risk_ledger.json --objective balanced_accuracy

ext_runtime_risk_ledger operates on pi.ext.runtime_risk_ledger.v1 artifacts (for example, from incident bundle exports).

Release & Publishing

Releases are tag-driven and must align with Cargo.toml versions.

Tag format: vX.Y.Z (pre-releases like vX.Y.Z-rc.N are allowed but skip crates.io publish).
The tag version must match package.version in Cargo.toml.
Publish order for dependencies: asupersync → rich_rust → charmed-* (lipgloss, bubbletea, bubbles, glamour) → pi_agent_rust.
.github/workflows/publish.yml handles crates.io publish when CARGO_REGISTRY_TOKEN is set.

Coverage

Coverage uses cargo-llvm-cov:

# One-time install
cargo install cargo-llvm-cov --locked
rustup component add llvm-tools-preview

# Summary (fastest)
cargo llvm-cov --all-targets --workspace --summary-only

# LCOV report (for CI/artifacts)
CI=true VCR_MODE=playback VCR_CASSETTE_DIR=tests/fixtures/vcr \
  cargo llvm-cov --all-targets --workspace --lcov --output-path lcov.info

# HTML report (defaults to target/llvm-cov/html)
cargo llvm-cov --all-targets --workspace --html

Project Structure

Selected core modules (non-exhaustive):

src/
├── main.rs                # CLI entry point
├── lib.rs                 # Library exports
├── app.rs                 # Startup/model selection helpers
├── agent.rs               # Agent loop + event orchestration
├── agent_cx.rs            # asupersync capability context wiring
├── cli.rs                 # Argument parsing
├── config.rs              # Configuration
├── auth.rs                # API key/OAuth/AWS credential storage
├── model.rs               # Message/content/stream event types
├── provider.rs            # Provider trait
├── provider_metadata.rs   # Canonical provider IDs + routing defaults
├── models.rs              # Model registry + models.json overrides
├── providers/
│   ├── anthropic.rs        # Anthropic Messages API
│   ├── openai.rs           # OpenAI Chat Completions
│   ├── openai_responses.rs # OpenAI Responses API
│   ├── gemini.rs           # Gemini API
│   ├── cohere.rs           # Cohere Chat API
│   ├── azure.rs            # Azure OpenAI
│   ├── bedrock.rs          # Amazon Bedrock Converse
│   ├── vertex.rs           # Google Vertex AI
│   ├── copilot.rs          # GitHub Copilot backend
│   ├── gitlab.rs           # GitLab Duo backend
│   └── mod.rs              # Provider factory + extension bridge
├── tools.rs                # Built-in tool implementations
├── sse.rs                  # Streaming SSE parser
├── http/
│   ├── client.rs           # asupersync-backed HTTP client
│   ├── sse.rs              # HTTP SSE helpers
│   └── mod.rs
├── session.rs              # JSONL session persistence/tree ops
├── session_index.rs        # SQLite session metadata index/cache
├── session_sqlite.rs       # Default-enabled sqlite-sessions backend support
├── compaction.rs           # Context compaction algorithm
├── interactive.rs          # Interactive TUI app loop/state
├── interactive/            # Bubble Tea-style TUI submodules
├── rpc.rs                  # RPC/stdio mode
├── extensions.rs           # Extension protocol + policy + security
├── extensions_js.rs        # QuickJS runtime bridge + hostcalls
├── extension_dispatcher.rs # Hostcall/tool dispatch plumbing
├── extension_preflight.rs  # Extension compatibility scanner
├── extension_validation.rs # Extension validation pipeline glue
├── resources.rs            # Skills/prompt/theme/extension loading
└── tui.rs                  # Terminal UI rendering helpers

Documentation Index

This index intentionally lists the load-bearing docs, not every generated snapshot under docs/. Historical planning and review material lives in the planning archive; see the docs classification record for the broader inventory.

Area	Primary docs
Getting started and operations	development, terminal setup, settings, models, keybindings, packages, troubleshooting, releasing
Core runtime surfaces	session, tree, TUI, RPC, SDK, skills, prompt templates, streaming hostcalls
Drop-in certification and migration	certification contract, certification verdict, parity gap ledger, differential evidence suite, feature inventory, migration playbook, parity snapshot, program governance
Extensions	architecture, compatibility guide, compatibility matrix, conformance plan, runtime threat model, troubleshooting, registry, WIT ABI
Providers	provider guide, auth troubleshooting, config examples, canonical ID policy, onboarding playbook, test obligations, upstream catalog snapshot, support baseline audit
QA and evidence	QA runbook, testing policy, conformance playbook, coverage matrix, evidence schema, coverage baseline map, E2E scenario matrix, non-mock rubric
Security	baseline audit, threat model, security invariants, operator handbook, operator quick reference, incident response, runtime hostcall telemetry, security SLOs
Schemas and machine contracts	extension manifest schema, extension protocol schema, session store v2 contract, test evidence logging contract, runtime hostcall telemetry schema, mock spec schema, CLI surface diff schema, security traceability matrix

About Contributions

Please don't take this the wrong way, but I do not accept outside contributions for any of my projects. I simply don't have the mental bandwidth to review anything, and it's my name on the thing, so I'm responsible for any problems it causes; thus, the risk-reward is highly asymmetric from my perspective. I'd also have to worry about other "stakeholders," which seems unwise for tools I mostly make for myself for free. Feel free to submit issues, and even PRs if you want to illustrate a proposed fix, but know I won't merge them directly. Instead, I'll have Claude or Codex review submissions via gh and independently decide whether and how to address them. Bug reports in particular are welcome. Sorry if this offends, but I want to avoid wasted time and hurt feelings. I understand this isn't in sync with the prevailing open-source ethos that seeks community contributions, but it's the only way I can move at this velocity and keep my sanity.

License

MIT License (with OpenAI/Anthropic Rider). See LICENSE for details.

_{Built with Rust, for developers who live in the terminal.}

Name		Name	Last commit message	Last commit date
Latest commit History 2,870 Commits
.beads		.beads
.cargo		.cargo
.github		.github
benches		benches
docs		docs
examples		examples
fuzz		fuzz
legacy_pi_mono_code/pi-mono/packages/ai/src		legacy_pi_mono_code/pi-mono/packages/ai/src
proptest-regressions		proptest-regressions
scripts		scripts
src		src
tests		tests
themes		themes
.gitignore		.gitignore
.rchignore		.rchignore
.ubsignore		.ubsignore
AGENTS.md		AGENTS.md
CHANGELOG.md		CHANGELOG.md
Cargo.lock		Cargo.lock
Cargo.toml		Cargo.toml
LICENSE		LICENSE
README.md		README.md
build.rs		build.rs
gh_og_share_image.png		gh_og_share_image.png
install.sh		install.sh
pi_agent_rust_illustration.webp		pi_agent_rust_illustration.webp
rust-toolchain.toml		rust-toolchain.toml
uninstall.sh		uninstall.sh
verify		verify

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