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/plugin_context.py

@@ -923,7 +923,19 @@ async def build_write_path_hint(
             )
         except Exception:
             logger.warning("Write-path ledger stamping failed", exc_info=True)
-    if not synced and not menu and not stamped:
+    # The in-band button-B check (#2793): the hook named the shapes being
+    # written; if this directory+kind is canon-dense and a named shape isn't
+    # (about to be) an instance of that canon, say so NOW — at the write,
+    # not at the next audit.
+    divergence: list[dict] = []
+    if stamp_shapes and project_id:
+        try:
+            divergence = await shape_ledger_svc.write_time_divergence(
+                project_id, path, stamp_shapes, stamped
+            )
+        except Exception:
+            logger.warning("write-time divergence check failed", exc_info=True)
+    if not synced and not menu and not stamped and not divergence:
         return empty
 
     owners = await owner_names_for({
@@ -989,6 +1001,8 @@ async def build_write_path_hint(
 
     if stamped:
         lines.append(_stamp_line(path, stamped))
+    if divergence:
+        lines.append(_divergence_line(path, divergence))
 
     # Split by arm, which is the whole reason this table exists. The place arm
     # carries no score and so has no home in retrieval_logs; before #2085 a
@@ -1012,9 +1026,26 @@ async def build_write_path_hint(
         "sync_note_ids": sync_note_ids,
         "config": cfg,
         "stamped": stamped,
+        "divergence": divergence,
     }
 
 
+def _divergence_line(path: str, divergence: list[dict]) -> str:
+    """Button B where button A is canon — named at the write (#2793)."""
+    parts = [
+        f"`{('.' if d['kind'] == 'css' else '') + d['symbol']}` → #{d['canon_snippet_id']} "
+        f"({d['instances']} of {d['judged']} judged siblings are its instances)"
+        for d in divergence
+    ]
+    return (
+        f"> Divergence check at `{path}`: a canon dominates this directory — "
+        f"{'; '.join(parts)}. If this is a new instance, pull that snippet "
+        "and build from it; if it is a deliberate departure, "
+        "`classify_shapes(..., status=\"variant\", reason=…)` records the why; "
+        "otherwise it reads as unintended divergence."
+    )
+
+
 def _stamp_line(path: str, stamped: list[dict]) -> str:
     """One line saying what the ledger just recorded, so the session can
     correct a wrong stamp in the moment rather than an audit finding it."""