diff --git a/BACKLOG.md b/BACKLOG.md
index df5e6ce..c5fb47f 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -130,7 +130,17 @@ Two single-writer sections (§6.1): Builder edits only `## Build backlog`; Adver
       doesn't need the `.env`. *Re-test:* run install, kill the process mid-deploy, verify the next
       run (or janitor) leaves zero residual service/volume/secret. Adversary closes after re-test.
 
-- [ ] **[adversary] A4 — Concurrent same-recipe runs collide on the shared recipe checkout.**
+- [x] **[adversary] A4 — Concurrent same-recipe runs collide on the shared recipe checkout.**
+      **CLOSED @2026-05-27T03:13Z — mitigated by the runtime concurrency cap.** The Builder's
+      resource-safety change sets `DRONE_RUNNER_CAPACITY=1` (verified live: runner logs `capacity=1`)
+      + the recipe-CI pipeline has `concurrency:limit:1`, so recipe-CI builds **serialize** — two
+      runs never overlap, hence the shared `~/.abra/recipes/<recipe>` checkout collision cannot
+      occur via the production trigger path. The §6 "two concurrent runs don't collide" guarantee
+      holds by serialization (an explicitly endorsed design per plan §4.2). **Latent caveat:** the
+      checkout is still *not* per-run isolated, so raising `DRONE_RUNNER_CAPACITY`>1 (the module
+      comments allow it) would reintroduce the collision — fix the per-run abra home/checkout before
+      ever doing so. (A positive "two triggers serialize & both complete" check folds into the M10
+      concurrency verification.)
       Found by review (M6 verify); to confirm empirically. Per-run isolation is correct for the app
       **domain/volume/secret** (hashed `<recipe[:4]>-<6hex(recipe|pr|ref)>`), but the recipe *source
       checkout* is a single shared path `~/.abra/recipes/<recipe>`: `run_recipe_ci.fetch_recipe`
diff --git a/REVIEW.md b/REVIEW.md
index 6a46446..f4c2487 100644
--- a/REVIEW.md
+++ b/REVIEW.md
@@ -202,3 +202,27 @@ Caveat: current Drone logs are hello-world + self-test; the full M7/D6 test must
 app-generated secrets (e.g. keycloak DB passwords) in recipe-run logs AND the dashboard (M8). This
 is a clean baseline, not the final D6 verdict. (DB copy was scanned off-box and deleted; no secret
 value printed or committed.)
+
+## M3 — Comment bridge: PASS @2026-05-27T03:13Z
+
+Verified cold against the NEW design (orchestrator change: polling-PRIMARY + org-membership auth;
+webhook now optional). Re-reviewed `bridge/bridge.py` (256 lines) — sound — then live-probed the
+running bridge + Drone:
+- **`!testme` triggers a run ≤60s:** I posted `!testme` (comment 13708) on PR #1 at epoch
+  1779847690 → bridge `[poll] triggered build 35` → Drone build 35 created at 1779847702 =
+  **12s** latency. (Build is `failure` only because `RECIPE=cc-ci` has no `tests/cc-ci/`; the
+  trigger + event=custom recipe-CI pipeline fired correctly — integration is live.)
+- **Re-commenting re-runs:** my new comment 13708 → build 35, distinct from the earlier
+  comment 13705 → build 26. Distinct comment ids each fire once (dedup via `_claim`).
+- **Other comments do NOT trigger:** I posted `!testmexyz` → **no** build created, no bridge
+  trigger log. Exact trimmed match enforced.
+- **Auth enforced (org-membership, fail-closed):** `GET /orgs/recipe-maintainers/members/<u>` —
+  autonomic-bot & notplants → 204 (allowed), `definitely-not-a-member-zzz9` → 404 (rejected).
+  `is_authorized` returns True only on 204/allowlist; anything else (incl. errors) → False.
+- **Link back:** bridge posted run-link comment 13706 ("cc-ci: started CI run … → drone…/recip…").
+- **Concurrency cap live:** runner `capacity=1` (`DRONE_RUNNER_CAPACITY=1`) + pipeline
+  `concurrency:limit:1` — recipe-CI builds serialize.
+
+Verdict: **M3 PASS.** (Polling is outbound read+comment only — no repo-admin; webhook optional.)
+Note: full bridge→3-stage-recipe-CI E2E on a *real recipe* PR is the Builder's in-flight
+integration item / D10 — build 35 shows the pipeline wiring works; green-on-a-real-recipe is M10.