feat: operationalize frontend incident runbooks

docs/runbooks/FE-RB-005.md

@@ -0,0 +1,13 @@
+# FE-RB-005 — Coherent release rollback
+
+Trigger on a release-blocking boot, chunk, render, API, or security defect when
+a safe forward fix is not demonstrated inside the incident window. Select a
+prior immutable release, verify its asset/config/API tuple, atomically switch
+the complete set, perform the provider cache action, and run smoke checks.
+Escalate from the release-cache owner to the release approver/hosting owner.
+The provider recovery target remains TBD until hosting is selected.
+
+Close only when compatibility and release-coherence gates pass, critical smoke
+passes, repeated `DEPLOY_MISMATCH` is absent, and the incident timeline records
+the restored release ID. Pointer-switch or cache-purge completion alone is not
+recovery evidence.