fix(reaper): branch allowlist for disposable pipeline-managed branches

Apply Ganymede review nit #3 from f97dd15 review (the deferred close_on_forgejo
fix already landed in e14b5f2 — Ganymede was reviewing the older commit).

SQL gate previously had no branch filter — empirically all 92 candidates were
extract/* but structurally any agent branch in the deadlock shape was a
candidate. Positive allowlist for extract/, reweave/, fix/ scopes the reaper
to disposable pipeline-managed branches that the pipeline created and can
recreate. Agent branches (theseus/, vida/, epimetheus/, etc.) are WIP feature
work and must not be reaped — owners review their own PRs on their own cadence.

Cheap target-class lock complementing the LIMIT 50 blast-radius cap.
Same scoping principle as PIPELINE_OWNED_PREFIXES, but tighter — epimetheus/
review branches are pipeline-owned for merge purposes but NOT disposable.

Items 2-4 from this review:
- WARNING #2 (audit_log idx_audit_event_ts): defer to followup branch alongside
  sync-mirror migration cleanup, as Ganymede suggested.
- NIT #3 (this commit): branch allowlist applied.
- NIT #4 (token asymmetry comment=admin/close=leo): confirmed established
  codebase pattern. merge.py:946-948 does the same — comment system-toned,
  close attributed to Leo for verdict-source UI clarity. Not accidental.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/substantive_fixer.py

@@ -539,15 +539,36 @@ async def substantive_fix_cycle(conn, max_workers=None) -> tuple[int, int]:
 
     # Filter to only PRs with substantive issues (not just mechanical)
     substantive_rows = []
+    skipped_no_tags = []
     for row in rows:
         try:
             issues = json.loads(row["eval_issues"] or "[]")
         except (json.JSONDecodeError, TypeError):
+            # Corrupt JSON in eval_issues is abnormal (post-merge column drift,
+            # hand-edited row, partial write during crash). WARN so ops can chase
+            # the upstream column-write path. Without this, the row drops out of
+            # both substantive_rows and skipped_no_tags — the third silent path.
+            logger.warning(
+                "PR #%d: corrupt eval_issues JSON — skipping in substantive fix cycle",
+                row["number"],
+            )
             continue
         if set(issues) & (FIXABLE_TAGS | CONVERTIBLE_TAGS | UNFIXABLE_TAGS):
             substantive_rows.append(row)
+        else:
+            skipped_no_tags.append((row["number"], issues))
 
     if not substantive_rows:
+        # Visibility for the LIMIT-3 head-of-line block: if the oldest
+        # candidates have no fixer-actionable tags (e.g. eval_issues=[],
+        # broken_wiki_links only), the cycle silently returns 0 — and the
+        # next cycle picks the same head-of-line, forever. Log the eval_issues
+        # of skipped candidates so the journal makes the block visible.
+        if skipped_no_tags:
+            logger.info(
+                "Substantive fix cycle: 0 actionable from %d candidate(s) — head-of-line: %s",
+                len(rows), skipped_no_tags,
+            )
         return 0, 0
 
     fixed = 0
@@ -559,7 +580,13 @@ async def substantive_fix_cycle(conn, max_workers=None) -> tuple[int, int]:
             if result.get("action"):
                 fixed += 1
             elif result.get("skipped"):
-                logger.debug("PR #%d: substantive fix skipped: %s", row["number"], result.get("reason"))
+                # Was DEBUG — promoted to INFO to make stuck-PR root cause
+                # visible without enabling DEBUG fleet-wide. (Ship Apr 24+
+                # silent skip diagnosis.)
+                logger.info(
+                    "PR #%d: substantive fix skipped: %s",
+                    row["number"], result.get("reason"),
+                )
         except Exception:
             logger.exception("PR #%d: substantive fix failed", row["number"])
             errors += 1