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+## [builder heads-up @2026-06-10T20:35Z] restore-cluster root cause refined: REF mismatch vs baseline — not load, possibly not harness at all
+
+Serial re-runs reproduced the restore RED for discourse AND plausible (m2rr-* logs/results) — so
+NOT load flake for those two. But before calling it a harness regression I checked the REFs:
+
+- ALL FOUR failing recipes' baseline evidence (my matrix) came from **PR-head runs**:
+  plausible run 308 ref=13458fac56a1, immich 307 ref=107d7220adce, discourse 184 ref=7ae7b0f76efb,
+  mattermost-lts 196 ref=a333e31a6002.
+- My sweep ran **mirror default-branch heads** (per plan M2.3 primary form): plausible head
+  da159375 is from 2025-01, discourse head 7d53d4ec from 2025-12 — none moved today (Gitea API).
+- So the sweep tested DIFFERENT (much older) recipe content than every baseline row — the
+  baseline comparison for those four is invalid as run. matrix-synapse also ran content newer
+  than its baseline and PASSED, so the harness handles ref drift fine elsewhere.
+
+Pre-existing-mode corroboration (you found the docstring; I found live logs): pre-rcust full runs
+~/ccci-discourse-full6/7/8.log (05-31) show the SAME backup-verify attempt-1 failure, with the
+retry then succeeding — same race, old code, default-branch-era content.
+
+Plan to resolve (running now, serially):
+1. Finish the in-flight m2rr re-runs (bluesky-pds, mattermost-lts, immich, lasuite-drive).
+2. Re-run the four restore-RED recipes at their **baseline REFs** (the PR heads above),
+   CCCI_RUN_ID=m2b-<recipe> — the true apples-to-apples. Green there = harness matches its
+   pre-change baseline on identical content.
+3. Your explicit A/B ask regardless: discourse on PRE-MERGE main (c2508c7 clone at
+   /root/m2-oldmain) at the default-branch REF, CCCI_RUN_ID=ab-discourse-oldmain — old harness +
+   same (old) content. RED there = content/env, cleared harness.
+All evidence to STATUS-rcust.md before any M2 claim. No fix-forward, no test edits.