[BoozeLee]

What this PR adds

harness verify --embed-repro now writes a stable reproducibility block into the evidence JSON it produces, alongside the existing task, goal, accept, results, files, stat, verdict, time fields.

{
  "captured_at": "2026-10-11T10:23:32+00:00",
  "harness_sha": "cd10f245519756198fe9c5e37baf414cdeedb07f",
  "harness_version": "1.1.0",
  "python_version": "3.11.9",
  "python_implementation": "CPython",
  "platform": "Linux-7.2.9-zen1-1-zen-x86_64-with-glibc2.44",
  "host": "omarchy",
  "packages_sha256": null,
  "packages_count": null,
  "github_sha": null,
  "github_run_id": null,
  "github_run_attempt": null
}

Stable across consecutive invocations on the same machine: harness_sha, harness_version, python_version, platform, host, packages_sha256, packages_count. The only wall-clock field is captured_at. The GitHub-Actions fields (github_sha, github_run_id, github_run_attempt) come from os.environ and pick up automatically in CI.

Why it matters

Evidence is the single artifact that flows from harness verify to reviewers, dashboards, and PR-merge gates. Today, an evidence JSON says what passed; tomorrow's reviewer also needs which build of harness, on which Python, on which host passed. The repro block makes evidence self-describing — six months later, anyone holding the JSON can prove what runtime produced it. This is the smallest possible cross-cutting substrate for the larger cross-repo verification story in the org's Q4 roadmap (STRATEGY.md in Quattro-Commas.github.io).

Files

File	Change	Why
harness/repro.py (new)	+108 lines	embed_repro_metadata(root, *, harness_sha=None) -> dict. Total contract — never raises; missing data lands as None.
harness/verify.py	+3 lines	cmd_verify writes ev["repro"] = embed_repro_metadata(r) when a.embed_repro is set.
harness/cli.py	+2 lines	--embed-repro flag on the verify subparser (default off, no behaviour change for existing callers).
harness/evidence.py	+24 lines	render adds an optional Reproducibility section to the HTML evidence.
tests/test_repro.py (new)	+123 lines	10 tests pin the shape, type, stability, override, GitHub-env propagation, and never-raise contract.

Tests

• uv run pytest -q tests/test_repro.py → 10 passed
• uv run pytest -q (full suite) → ~104 passed
• uv run ruff check (4 touched files) → clean
• uv run mypy harness/repro.py → no issues

Behaviour change

None for existing callers. --embed-repro is opt-in; default off. A re-run of any current harness verify invocation produces byte-identical evidence.

Follow-ups (out of scope here)

• runner.py:_verify_run parity — the same flag wired through serve/the API. Today, only the CLI path emits repro; the dashboard inherits nothing until that lands.
• Plumbing through the task contract so harness task start --embed-repro makes repro part of the contract (no longer passed per-invocation).