feat(infra): Railway Vivado self-hosted GH Actions runner

[gHashTag]

Summary

Provisions a managed x86_64 Linux runner with Vivado 2025.2, registered as a self-hosted GitHub Actions runner against t27. Unblocks PR #604 (Vivado-CI with UART telemetry) and tok/s measurement on silicon.

What ships

infra/railway-vivado-runner/

• Dockerfile — Ubuntu 22.04 + Vivado deps (libtinfo5/libncurses5/libstdc++ etc.) + GH Actions runner v2.319.1 + Rust toolchain for entrypoint build.
• src/main.rs — Rust entrypoint binary (runner-entrypoint). Registers runner with GH if no .runner config exists, sources Vivado settings64.sh into env, exec's ./run.sh (GH-supplied). No bash entrypoint.sh per project policy: запрешены .sh .py.
• Cargo.toml — entrypoint crate (anyhow only).
• railway.toml — 3 persistent volumes: /opt/Xilinx (130 GB Vivado install), /opt/installer (1 GB installer drop), /actions-runner/_work (20 GB cache).
• README.md — 9-step deploy runbook: railway init → volumes → Vivado installer push → token fetch → env vars → railway up → silent Vivado install → verification.

.github/workflows/vivado-self-hosted.yml

• runs-on: [self-hosted, vivado, x86_64, linux]
• Builds t27c, generates Verilog from .t27 specs via fpga-build --smoke, runs Vivado synth, optionally runs UART smoke if DLC-10 JTAG attached (gated by LANES_ATTACHED=1).
• Triggers on PR (paths fpga/, specs/fpga/, bootstrap/, the workflow itself) + manual dispatch with design selection (blinky / gf16 / phi_heartbeat) and UART toggle.
• Extracts utilization summary (LUTs, Registers, BRAM, DSP, WNS) via inline awk from vivado.log.

Why Railway

M4 Mac (228 GB SSD, ~11 GB free, ARM64) cannot host Vivado: needs ~110 GB and x86_64. Railway provides managed x86_64 Linux containers with persistent volumes. Tailscale already configured Mac-side for any reverse access if needed.

Operator next steps

See infra/railway-vivado-runner/README.md. After merge:

1. cd infra/railway-vivado-runner && railway init
2. Provision 3 volumes per railway.toml
3. railway volume push ~/Downloads/Vivado_2025.2_Lin64.bin /opt/installer/
4. Get fresh runner registration token from repo Settings → Actions → Runners
5. railway variables set GH_RUNNER_TOKEN=… GH_REPO_URL=https://github.com/gHashTag/t27
6. railway up
7. One-time railway run /opt/installer/Vivado_2025.2_Lin64.bin --batch Install …
8. Verify runner Online; trigger vivado-self-hosted.yml with design=blinky

Cost

~$35–55/month Railway Pro (8 vCPU / 32 GB / 150 GB).

Policy compliance

• ✓ no .sh / .py (Rust entrypoint binary)
• ✓ no Cyrillic in docs/architecture/specs paths
• ✓ Refs infra: Railway Vivado self-hosted GH Actions runner #620, Refs feat(fpga): Vivado CI pipeline for gf16_heartbeat_uart_top (UART telemetry on K20) #604 in commit message

Refs #620
Refs #604

[github-actions]

📓 NotebookLM Notebook linked to this PR

• Notebook ID: b83263109fb055dc
• URL: https://notebooklm.google.com/notebook/b83263109fb055dc

This notebook contains session context, decisions, and artifacts for this work.

[gHashTag]

Superseded by #622 — Vivado moved to GitHub Actions Docker (no Railway, no self-hosted runner, $0/month). Closing this PR.