journal(conc): tests suite + P5 evidence, M1 claim context

JOURNAL-conc.md

@@ -47,3 +47,18 @@ via a git worktree at ../cc-ci-conc; test runs on the cc-ci host via /root/build
   One stale comment line (.drone.yml l.39 "concurrency.limit=2 below") folds into P5.
 
 All four commits: tests/unit 138 passed + lint PASS before each. Next: tests/concurrency suite.
+
+## 2026-06-10 — tests/concurrency (84d90fb) + P5 (d3fe9e2) + M1 claim (e8e52cf)
+
+- Suite: 20 tests / 19 plan cases, all real-kernel (helpers.py subprocesses hold real flocks,
+  install real prctl/alarm guards; CCCI_APP_LOCK_DIR sandboxes /run/lock; HelperPool reaps every
+  helper + recorded grandchildren). First full run on cc-ci: 20 passed in 9.96s, zero flakes in
+  3 repeat runs during the P5 verification re-runs.
+- Design notes for the Adversary's blind-spot hunt (my own known limits):
+  - case 8 (two janitors) uses threads in one process — valid because flock conflicts are
+    per-open-file-description, and overlap is forced via a Barrier + 2s slow teardown stub.
+  - case 14 relies on reparent-to-pid-1 (true on the cc-ci host; would need adjustment in a
+    subreaper environment — marked NEVER_REPARENTED visibly if so).
+  - cases 5-12 stub teardown_app (recording) — janitor probe/reap ordering is what's under
+    test, not teardown internals (covered by Phase-1 e2e + M2 live checks).
+- M1 claimed at e8e52cf; full verification recipe in STATUS-conc.md (WHAT/WHERE/HOW/EXPECTED).