fix(ci): gate extract-claude-lessons on head branch, not PR author

[shuheng-liu]

What this does

.github/workflows/extract-claude-lessons.yml was added in #199 but
its if: gate has never let a job run. The previous condition was:

if: >-
  github.event.pull_request.merged == true
  && contains(github.event.pull_request.user.login, 'claude')
  && !startsWith(github.event.pull_request.title, 'chore(claude): learn from')

Two notes on why this was failing — both from looking at the recent
merged PRs (#171, #178, #182, #183, #189, #190, #198, #199, #204, #207,
#208, #209, #206):

1. [closed] is the right trigger — there is no [merged] action
   type for pull_request in GitHub Actions. closed fires for both
   close-without-merge and merge, and the merged == true check
   correctly narrows it. So the trigger isn't the bug.
2. user.login is the wrong field. In this repo, Claude Code on
   the web pushes to a claude/<slug> branch, then a human (e.g.
   shuheng-liu) opens the PR. So pull_request.user.login is the
   human, never claude*, and contains(..., 'claude') is always
   false. The reliable signal is the head branch prefix, which is
   under Claude Code's control.

This PR swaps the filter to startsWith(head.ref, 'claude/'). Backfill
across the 14 most-recent merged PRs:

filter	match count
contains(user.login, 'claude') (old)	0
startsWith(head.ref, 'claude/') (new)	13

Tag: 🐛 Bug

How it was tested

• Confirmed via the GitHub API (gh api .../pulls?state=closed) that
  every recent PR's user.login is the human reviewer's login and
  every Claude-touched PR's head.ref starts with claude/.
• Verified the YAML still parses (only the boolean expression in the
  if: changed).
• Did NOT run pre-commit run --all-files — the sandbox this PR was
  authored in has no pre-commit binary. Please run it locally if the
  CI hook complains.
• No runtime code changed, so no pytest was run.
  tests: skipped — workflow YAML condition only, no Python touched.

How to checkout & try? (for the reviewer)

The workflow only fires on pull_request: closed, so the real test is
to merge this PR and watch the next merged claude/* PR — the
extract-lessons job should now appear in the Actions tab and either
open a chore(claude): learn from #N PR or exit cleanly.

git fetch origin claude/fix-ci-closed-prs-LnVFT
git diff main...origin/claude/fix-ci-closed-prs-LnVFT -- .github/workflows/extract-claude-lessons.yml

Checklist

• I have added Google-style docstrings to important functions and ensured function parameters are typed.
• My PR includes policy-related changes.
  • If the above is checked: I have run the GPU pytests (pytest -m "gpu") and regression tests.

(This PR only touches a single GitHub Actions YAML file — no Python
functions are added or changed, so the docstring item is vacuously
satisfied. The policy-changes box is correctly unchecked.)

Note: Before submitting this PR, please read the contributor guideline.

[claude]

Confirmed via gh api /repos/TensorAuto/OpenTau/pulls?state=closed: every recently merged PR has user.login = shuheng-liu and head.ref starting with claude/, matching the PR description's backfill table. The new gate (startsWith(github.event.pull_request.head.ref, 'claude/')) is the right signal.

A few notes:

• pull_request.head.ref is the bare branch name (no refs/heads/ prefix), so startsWith(..., 'claude/') is the correct comparison.
• Recursion guard is unchanged (the chore(claude): learn from title check), so lessons-extraction PRs — which would also be on claude/* branches — still won't loop.
• The change is workflow-YAML only; the PR explicitly defers pre-commit and pytest. That's appropriate here — the only way to truly validate is to merge and watch the next merged claude/* PR.

No blocking issues found.

[claude]

[claude-review] summary for commit cd6a496

No blocking issues found.

• nit — .github/workflows/extract-claude-lessons.yml:34 — head.ref is the right field and startsWith(..., 'claude/') is the right matcher; backfill in the PR description (13/14 recent merged PRs) is verified against the live API.