fix(fleet): fail closed on persona overrides

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/scratchpads/758-fcm-m1-002-shared-role-resolution.md

@@ -72,6 +72,36 @@ compatibility and canonical collision denial.
 - Independent security review: **APPROVE**, no verified authority/security findings on the final
   delta.
 
+### Post-PR fail-closed remediation
+
+Independent rereview found resolver fail-open edges that the original green PR head did not cover. The
+remediation remained uncommitted until every finding was reproduced red-first and the same reviewer
+approved the complete two-file delta.
+
+Final regression evidence:
+
+```text
+persona resolver: 47/47
+focused affected suites: 6 files / 138 tests
+root-container resolver suites: 86/86
+full canonical run: 42/42 Turbo tasks; Mosaic 50 files / 733 tests
+```
+
+DB migration, typecheck, lint, Prettier, and `git diff --check` also passed. Coverage now proves:
+
+- unreadable, unscannable, direct-dangling, ancestor-dangling, and literal `..` traversal override paths
+  fail closed across async, sync, listing, and status APIs;
+- genuinely missing override directories still permit baseline fallback;
+- cached missing scans are revalidated before fallback;
+- marker-defined identity and domain metadata are revalidated on the second read;
+- `LIBRARY.md` rows and incidental later markers cannot define, shadow, or advertise personas.
+
+Final independent finding-specific rereview: **APPROVE**. The reviewer verified exact absolute and
+relative dangling-ancestor traversal, cached-missing revalidation, second-read marker identity, and
+async/sync/list/status behavior. The source remained at remote head `1c41adad…` during remediation;
+a fresh pushed head still requires terminal-green CI and durable exact-head reviewer-of-record before
+merge.
+
 
 ## Risks and boundaries