feat: provenance-drift check + re-pin for project→assistant refer-back

[Jammy2211]

Summary

Completes #43 — the last missing mechanic of the science-project → assistant refer-back model locked in skills/start-new-project.md. A project resolves the assistant clone at run time ($AUTOLENS_ASSISTANT → sibling → clone-on-demand) but pins assistant_ref at creation; nothing compared the two. This adds the non-blocking provenance-drift check: after resolution, compare the clone's commit to project.yaml's assistant_ref.commit; on mismatch, warn once per session (both commits + what drift means), offer a re-pin recorded as one line in the day's wiki/project/ journal entry, and never hard-block or check out the pinned commit — the per-run manifest's assistant.commit remains the record of what was actually used. The generated thin AGENTS.md template carries a one-line mirror so a copilot invoked inside a project performs the check without reading this skill first.

Start_dev audit note: the prompt's other three bullets (resolution order, AUTOLENS_ASSISTANT env var, assistant_ref pin + manifest provenance) were already shipped in this skill on main — this PR implements only the genuinely missing fourth.

API Changes

None — markdown-only change to one skill (the locked design doc + its generated templates). No Python surface.

Test Plan

• pytest autoassistant/tests -q — 39 passed
• autoassistant/audit_skill_apis.py — 57 files, 117 symbols, 0 missing/broken
• --check-citations — 90 files, 388 citations, 0 missing paths
• Consistency pass: section cross-references resolve; assistant_ref.commit / manifest assistant.commit key names match the templates in the same file

Validation checklist (--auto run — plan was not pre-approved)

• Effective level: safe (header: safe, cap: feature/small → safe)
• Plan: on the issue (feat: project provenance-drift warning + re-pin for assistant refer-back #43), written at start, unmodified since
• Gate: tests 39 pass + symbol/citation audits clean · smoke n/a (markdown-only skill edit, no downstream script surface) · review CLEAN (review-faculty surface: 1 commit, 1 file, +14; consistency + citation checks in lieu of runtime verify for a doctrine diff) · Heart YELLOW within launch ack (6 reasons, exact set recorded in the task's active.md heart-ack: block)
• Human: plan sound in hindsight?
• Human: diff matches plan (no scope creep)?
• Human: merge, amend, or reject — then log the outcome

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