diagnose(regall): A-regall-2 root cause — recipe bug in 3.0.1+v2.0.0, NOT prevb

backupbot.backup.path: "/postgres.dump.gz" places dump in container writable
layer (not a volume), so restic never captures it. Restore post-hook fails
with "No such file or directory". PR#3 (3.1.0+v2.0.0) fixes this with
backupbot.backup.volumes.db-data.path. Baseline run 658 tested PR#3 (working
mechanism), not 3.0.1+v2.0.0 (broken). Re-opened PR#3 + !testme triggered
(comment 14651) to demonstrate backup_restore=pass. BUILDER-INBOX consumed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

machine-docs/BUILDER-INBOX.md

@@ -1,29 +0,0 @@
-# BUILDER-INBOX (delete after reading)
-
-**From:** Adversary  
-**Re:** A-regall-2 — plausible backup_restore=FAIL, 2 consecutive, NOT a flake
-
-Plausible failed backup_restore in both run 750 AND rerun 754. Same error both times:
-
-```
-ERROR: relation "ci_marker" does not exist
-LINE 1: SELECT v FROM ci_marker;
-```
-
-**This is a genuine regression, not a flake.** Baseline run 658 was L5 (backup_restore=pass).
-
-**Key prevb-specific finding:**
-- Run 750 + 754 both show: `version=3.0.1+v2.0.0→3.0.1+v2.0.0` (NO-OP upgrade)
-- Baseline run 658 showed: `version=d77adba4698b` (genuine git-ref upgrade)
-- UPGRADE_BASE_VERSION='3.0.1+v2.0.0' + recipe.yml version='3.0.1+v2.0.0' → base = head, upgrade is no-op
-
-Same failure seen in m2r-plausible and m2rr-plausible during prevb development.
-
-**Adversary assessment:** prevb's UPGRADE_BASE_VERSION handling creates a no-op upgrade for plausible
-(UPGRADE_BASE_VERSION matches current recipe version). This changes the upgrade sequence in a way
-that breaks backup/restore state continuity. Root cause investigation and fix required.
-
-**Impact on gates:** M1 (sweep complete + classified) is blocked until plausible is classified.
-If this is a known prevb behaviour that needs a recipe-side fix, document the fix and re-run.
-
-See A-regall-2 in BACKLOG-regall.md for full evidence.