docs: add CLAUDE.md, architecture docs, and /sesh-mode skill

.claude/skills/sesh-mode/SKILL.md

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+---
+description: "Verification-first development workflow with TLA+ specs, DST, and formal methods. Use when you want Claude to follow the rigorous plan→spec→test→implement sequence."
+user-invocable: true
+---
+
+# Sesh Mode — Verification-First Development
+
+Activate this mode when working on features that touch state machines, protocols, or critical data paths. This adds formal verification requirements on top of the base CLAUDE.md.
+
+## Before Writing Any Code
+
+**MUST** follow this sequence before implementation:
+
+1. **Define the plan**: What are you doing and why? What invariants must hold?
+2. **Check ADR/roadmap**: `docs/internals/adr/README.md` → find relevant supplement
+3. **Read the spec**: If touching state machines or protocols, read `docs/internals/specs/tla/*.tla`
+4. **Write tests first**: DST tests define correctness, write them before code
+5. **Only then**: Start implementation
+
+## Three Engineering Pillars
+
+Every code change **MUST** respect all three:
+
+| Pillar | Location | Purpose |
+|--------|----------|---------|
+| **Code Quality** | [CODE_STYLE.md](../../../CODE_STYLE.md) + CLAUDE.md | Coding standards & reliability |
+| **Formal Specs** | `docs/internals/specs/tla/`, `stateright_*.rs` | Protocol correctness |
+| **DST** | DST crate (when created) | Fault tolerance |
+
+**Priority**: Safety > Performance > Developer Experience
+
+## The Verification Pyramid
+
+All verification layers share the same invariants:
+
+```
+         TLA+ Specs (docs/internals/specs/tla/*.tla)
+                    │ mirrors
+         Shared Invariants (invariants/)  ← SINGLE SOURCE
+                    │ used by
+    ┌───────────────┼───────────────┐
+    ▼               ▼               ▼
+Stateright      DST Tests      Production Metrics
+(exhaustive)    (simulation)   (Datadog)
+```
+
+## Testing Through Production Path
+
+**MUST NOT** claim a feature works unless tested through the actual network stack.
+
+```bash
+# 1. Start quickwit
+cargo run -p quickwit-cli -- run --config ../config/quickwit.yaml
+
+# 2. Ingest via OTLP
+# (send logs/traces to localhost:4317)
+
+# 3. Query via REST API
+curl http://localhost:7280/api/v1/<index>/search -d '{"query": "*"}'
+```
+
+**Bypasses to AVOID**: Testing indexing pipeline without the HTTP/gRPC server, testing search without the REST API layer.
+
+## DST (Deterministic Simulation Testing)
+
+- DST tests define correctness for stateful components
+- Write DST tests before implementation for new state machines
+- Shared invariants are the single source of truth across all verification layers
+
+## Architecture Evolution
+
+Pomsky tracks architectural change through three lenses. See `docs/internals/adr/EVOLUTION.md` for the full process.
+
+```
+                    Architecture Evolution
+                            │
+       ┌────────────────────┼────────────────────┐
+       ▼                    ▼                    ▼
+ Characteristics          Gaps              Deviations
+  (Proactive)          (Reactive)          (Pragmatic)
+ "What we need"      "What we learned"   "What we accepted"
+```
+
+| Lens | Location | When to Use |
+|------|----------|-------------|
+| **Characteristics** | `docs/internals/adr/` | Track cloud-native requirements |
+| **Gaps** | `docs/internals/adr/gaps/` | Design limitation from incident/production |
+| **Deviations** | `docs/internals/adr/deviations/` | Intentional divergence from ADR intent |
+
+**Before implementing, check for**:
+- Open gaps (design limitations to be aware of)
+- Deviations (intentional divergence from ADRs)
+- Characteristic status (what's implemented vs planned)
+
+## Additional Commit Checklist (on top of CLAUDE.md MUST items)
+
+These are expected unless justified:
+- [ ] Functions under 70 lines
+- [ ] Explanatory variables for complex expressions
+- [ ] Documentation explains "why"
+- [ ] ADR/roadmap updated if applicable
+- [ ] DST test for new state transitions
+- [ ] Integration test for new API endpoints
+- [ ] Tests through production path (HTTP/gRPC)
+
+## Reference Documentation
+
+| Topic | Location |
+|-------|----------|
+| Verification & DST | [docs/internals/VERIFICATION.md](../../../docs/internals/VERIFICATION.md) |
+| Verification philosophy | [docs/internals/VERIFICATION_STACK.md](../../../docs/internals/VERIFICATION_STACK.md) |
+| Simulation workflow | [docs/internals/SIMULATION_FIRST_WORKFLOW.md](../../../docs/internals/SIMULATION_FIRST_WORKFLOW.md) |
+| Benchmarking | [docs/internals/BENCHMARKING.md](../../../docs/internals/BENCHMARKING.md) |
+| Rust style patterns | [docs/internals/RUST_STYLE.md](../../../docs/internals/RUST_STYLE.md) |
+| ADR index | [docs/internals/adr/README.md](../../../docs/internals/adr/README.md) |
+| Architecture evolution | [docs/internals/adr/EVOLUTION.md](../../../docs/internals/adr/EVOLUTION.md) |
+| Compaction architecture | [docs/internals/compaction-architecture.md](../../../docs/internals/compaction-architecture.md) |
+| Tantivy + Parquet design | [docs/internals/tantivy-parquet-architecture.md](../../../docs/internals/tantivy-parquet-architecture.md) |
+| Locality compaction | [docs/internals/locality-compaction/](../../../docs/internals/locality-compaction/) |