[docs] FOLLOWUPS: close squash-merge-trailer item with observation

docs/FOLLOWUPS.md

@@ -72,10 +72,17 @@ Highest-leverage opportunistic items, in order:
 
 ### Release / governance
 
-- [ ] **Verify squash-merge preserves `Assisted-by:` disclosure.**
-      AGENTS.md requires every commit authored with AI help to carry
-      an `Assisted-by:` trailer. *Trigger:* when M1.6's PR-13
-      actually merges — observe what the squash commit looks like.
+- [x] **Verify squash-merge preserves `Assisted-by:` disclosure.**
+      *Observed on PR-13 squash commit `a57883f`:* the per-commit
+      `Assisted-by:` trailers are NOT preserved as trailers on the
+      squash commit. The audit trail survives via the PR description
+      (which lists every source SHA) embedded in the squash body, but
+      the trailer-level disclosure AGENTS.md describes is gone. Two
+      follow-up paths, neither chosen here: (a) update AGENTS.md to
+      treat the PR-description SHA list as the canonical squash-merge
+      disclosure, or (b) switch AI-assisted PRs to merge-commit /
+      rebase-merge so per-commit trailers survive. **Policy decision
+      tracked but unchosen — flag for governance review.**
 
 ### Documentation
 
@@ -111,3 +118,6 @@ Highest-leverage opportunistic items, in order:
 
 - [x] **One-paragraph doc.go in `internal/pipelinebuilder`** — landed
       in PR #13 (see `internal/pipelinebuilder/doc.go`).
+- [x] **Verify squash-merge preserves `Assisted-by:` disclosure** —
+      observed on PR-13's `a57883f`; finding moved to "Release /
+      governance" above with the policy-decision flag.