feat(ledger): divergence readout — button B where button A is canon, shape history, and judged-shape recheck (#2793, milestone 294 step 7)

Every judgment now goes through one helper that remembers the fingerprint
judged (classified_sha) and writes a code_shape_events row; the sync writes
vanished / reappeared / drifted events and flags recheck_at when a body
moves under an instance/variant. The refresh flags diverges_from on shapes
new since the previous computation that sit where one canon dominates the
judged siblings of their directory+kind and were not proposed as that canon
(a first seed flags nothing); the write-path hint asks the same question
in-band for the shapes the hook names. list_shapes(flag=divergence|recheck),
shape_history(project_id, path, symbol) (read-only), coverage line/payload/
card carry divergent + recheck. Backup v8 carries the history. Plugin 0.1.36.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scribe/services/coverage.py

@@ -397,6 +397,18 @@ async def compute_coverage(
         await shape_ledger.apply_derive_groups(project_id)
     except Exception:
         logger.warning("derive-first grouping failed", exc_info=True)
+    # The button-B pass (#2793): shapes new since the PREVIOUS computation,
+    # where a canon dominates. The previous computation's stamp is the cache;
+    # a first seed has none, so it flags nothing (everything is new then).
+    try:
+        previous = await get_setting(user_id, f"{_CACHE_KEY_PREFIX}{project_id}")
+        since = None
+        if previous:
+            stamp = (json.loads(previous) or {}).get("computed_at")
+            since = datetime.fromisoformat(stamp) if stamp else None
+        await shape_ledger.flag_divergence(project_id, since=since)
+    except Exception:
+        logger.warning("divergence pass failed", exc_info=True)
 
     # Project-wide readout, deliberately wider than this walk: a second bound
     # repo that was unreachable today still has live rows, and they count.
@@ -413,6 +425,7 @@ async def compute_coverage(
 
     unclassified = counts.pop("unclassified")
     proposals = shape_ledger.proposal_summary(rows)
+    divergence = shape_ledger.divergence_summary(rows)
     return {
         "total": len(rows),
         "accounted": len(rows) - unclassified,
@@ -423,6 +436,11 @@ async def compute_coverage(
         "proposed": proposals["proposed"],
         "derive_groups": proposals["derive_groups"],
         "proposer": proposer_stats,
+        # The divergence readout (#2793): button B where button A is canon,
+        # and judged shapes whose bodies moved since they were judged.
+        "divergent": divergence["divergent"],
+        "divergence": divergence["divergence"],
+        "recheck": divergence["recheck"],
         # Honesty flag, not decoration: every surface that shows the number
         # is expected to carry it through.
         "estimate": True,
@@ -572,9 +590,13 @@ def coverage_line(coverage: dict) -> str:
         n_groups = len(coverage.get("derive_groups") or [])
         if n_groups:
             standing.append(f"{n_groups} derive group{'s' if n_groups != 1 else ''}")
+        if coverage.get("divergent"):
+            standing.append(f"{coverage['divergent']} DIVERGENT")
         if standing:
             line += f" ({', '.join(standing)})"
         gaps = [g["dir"] for g in coverage.get("largest_gaps") or []]
         if gaps:
             line += ", largest: " + ", ".join(gaps)
+    if coverage.get("recheck"):
+        line += f"; {coverage['recheck']} judged shape{'s' if coverage['recheck'] != 1 else ''} changed since judged — recheck"
     return line