feat(ledger): mechanical proposer — every refresh proposes instances against canon and groups derive-first candidates; agents confirm in batches (#2792, milestone 294 step 6)

Shapes now carry a content fingerprint (signature + whitespace/comment-
insensitive body_sha; migration 0080) and the proposer runs inside the
coverage refresh, the one moment bodies exist: symbol elsewhere → textual
containment → body references the canon → signature resemblance → semantic
(capped per refresh, unreached rows stay unexamined for the next). A hit is
a proposal on the row (proposed_snippet_id/basis/score), never a
classification; rows with no canon hit group by the derive-first rule
(identical body in ≥2 places, same name in ≥3 files) as proposal_basis=
derive + a group key. list_shapes(proposal=any|canon|derive|<basis>) is the
queue; confirm_shape_proposals(project_id, snippet_id|path|basis) confirms
in batches as agent instances; any classify_shapes/hook stamp retires the
proposal. Readout carries proposed + derive_groups (line, payload, card).
Plugin 0.1.35 (skill: the machine proposes, judgment classifies).

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

src/scribe/services/backup.py

@@ -1163,6 +1163,11 @@ async def _restore_v2(data: dict) -> dict:
                 first_seen_commit=cs_data.get("first_seen_commit", ""),
                 last_seen_commit=cs_data.get("last_seen_commit", ""),
                 vanished_at=_dt(cs_data["vanished_at"]) if cs_data.get("vanished_at") else None,
+                # Fingerprints restore; proposals (#2792) deliberately do not —
+                # they are mechanical, and the next refresh recomputes them
+                # against the restored snippet ids.
+                signature=cs_data.get("signature", ""),
+                body_sha=cs_data.get("body_sha", ""),
                 created_at=_dt(cs_data.get("created_at")),
                 updated_at=_dt(cs_data.get("updated_at")),
             ))