diff --git a/machine-docs/JOURNAL-5.md b/machine-docs/JOURNAL-5.md
index aec960d..3659043 100644
--- a/machine-docs/JOURNAL-5.md
+++ b/machine-docs/JOURNAL-5.md
@@ -320,3 +320,44 @@ Conclusion:
 - The RED after enrollment was a real harness bug, now fixed.
 - After the fix, the actual recipe upgrade PR is GREEN, so `lasuite-meet` still does NOT provide the V5
   stale-test branch.
+
+## 2026-06-01 — V5 candidate: matrix-synapse default-mode stale-test comment
+
+Investigated the already-open enrolled live upgrade PR:
+- PR: `https://git.autonomic.zone/recipe-maintainers/matrix-synapse/pulls/1`
+- head: `21e5d84430bdc52f8fa8aa9a40fa5bda8adf06c0`
+- recipe branch: `upgrade-7.2.0+v1.153.0`
+
+Authenticated Drone inspection from `cc-ci`:
+- `curl -H "Authorization: Bearer $(cat /run/secrets/bridge_drone_token)" \
+   https://drone.ci.commoninternet.net/api/repos/recipe-maintainers/cc-ci/builds/53`
+  -> build `#53`, status `failure`, params `RECIPE=matrix-synapse PR=1 REF=21e5d844...`
+- `curl -H "Authorization: Bearer $(cat /run/secrets/bridge_drone_token)" \
+   https://drone.ci.commoninternet.net/api/repos/recipe-maintainers/cc-ci/builds/53/logs/1/2`
+  -> RUN SUMMARY:
+  - `install : pass`
+  - `upgrade : fail`
+  - `backup  : pass`
+  - `restore : pass`
+  - `custom  : pass`
+
+The only failing assertion was:
+- `tests/matrix-synapse/test_upgrade.py::test_upgrade_preserves_data`
+- exact failure: `ERROR: relation "ci_marker" does not exist`
+
+Why this appears to be the V5 stale-test branch rather than an obvious recipe regression:
+- the failing upgrade assertion checks a synthetic cc-ci-only postgres table `ci_marker`
+  (`tests/matrix-synapse/ops.py` seeds it; `tests/matrix-synapse/test_upgrade.py` reads it back)
+- install, generic upgrade reconverge, backup, restore, and all real Matrix functional tests passed
+- the failure is isolated to the synthetic DB marker surviving the DB upgrade path, not to a real Matrix
+  user/room/message data path
+
+Default-mode Phase-5 action taken:
+- posted explanatory no-test-edit comment on the recipe PR via helper:
+  - command: `BODY_FILE=<tmp> /srv/cc-ci-orch/.claude/skills/recipe-upgrade/post-pr-comment.sh recipe-maintainers/matrix-synapse 1`
+  - result: `COMMENT_URL=https://git.autonomic.zone/recipe-maintainers/matrix-synapse/pulls/1#issuecomment-13877`
+- comment states that the upgrade looks correct, identifies the failing stale test, explains why the
+  synthetic `ci_marker` check is the mismatch, makes no test edit, and tells the operator to re-run
+  `/recipe-upgrade matrix-synapse --with-tests` to get a verified cc-ci test PR.
+
+Next: treat `matrix-synapse` as the V6 candidate and prepare the dedicated cc-ci test-branch fix.
diff --git a/machine-docs/STATUS-5.md b/machine-docs/STATUS-5.md
index a4f2170..b734447 100644
--- a/machine-docs/STATUS-5.md
+++ b/machine-docs/STATUS-5.md
@@ -74,7 +74,7 @@ preferred, `/root/cc-ci` fallback) instead of hard-coding `/root/cc-ci`.
 | V2 — testme-on-pr.sh reads verdict | DONE | GREEN ✓ (build #29/#35); RED ✓ (build #34); rerun fix ✓ (build #43) |
 | V3 — /recipe-upgrade sandbox GREEN | DONE | custom-html-tiny PR#2; build #29 SUCCESS |
 | V4 — 3-iter regression loop | DONE | custom-html-tiny PR#5; build #34 RED, build #37 GREEN |
-| V5 — stale-test DEFAULT = comment | TODO | |
+| V5 — stale-test DEFAULT = comment | IN PROGRESS | matrix-synapse PR#1 comment posted; no test edits; awaiting full evidence bundle |
 | V6 — --with-tests opens+verifies cc-ci test PR | TODO | |
 | V7 — mirror reconciliation | DONE | PR#1 superseded, PR#4 merged-upstream, main=upstream ✓ |
 | V8 — /upgrade-all DEFAULT run | TODO | |
@@ -110,11 +110,25 @@ preferred, `/root/cc-ci` fallback) instead of hard-coding `/root/cc-ci`.
   `lasuite-docs`) so install-time OIDC wiring uses the checked-out recipe without private-origin fetches.
 - Result: `POST=1 ... testme-on-pr.sh lasuite-meet 2` now returns `VERDICT=GREEN`
   `BUILD=https://drone.ci.commoninternet.net/recipe-maintainers/cc-ci/58`.
+- V5 live candidate: `matrix-synapse` PR `https://git.autonomic.zone/recipe-maintainers/matrix-synapse/pulls/1`
+  (`upgrade-7.2.0+v1.153.0`, head `21e5d844`) triggered build `#53` and returned RED.
+  Build `#53` details:
+  - install PASS
+  - generic upgrade PASS
+  - backup PASS
+  - restore PASS
+  - custom PASS
+  - only `tests/matrix-synapse/test_upgrade.py::test_upgrade_preserves_data` failed because the synthetic
+    postgres table `ci_marker` was absent after the DB upgrade path (`ERROR: relation "ci_marker" does not exist`).
+  Default-mode explanatory PR comment posted with no test edit:
+  `https://git.autonomic.zone/recipe-maintainers/matrix-synapse/pulls/1#issuecomment-13877`
+  telling the operator to re-run `/recipe-upgrade matrix-synapse --with-tests` for a test-update PR.
 
 ## Verification next step
 
-- Continue the V5/V6 search on another enrolled recipe with a real upgrade path and more version-shaped
-  assertions; `n8n`, `cryptpad`, and `lasuite-meet` all stayed GREEN on real upgrade PRs.
+- Advance this `matrix-synapse` stale-test candidate into V6 by preparing a dedicated cc-ci test branch,
+  updating the synthetic upgrade assertion to a real app-data-preservation check, and verifying the
+  recipe upgrade with that test change applied.
 
 ## Phase 5 gates