feat(family): the shape ledger judges against family ideas, across languages (milestone 463 step 5, #4991)

- classify_shapes takes idea_id: the shape is judged against the idea's
  reference in its language, or its first.
- A shape classified against a canon idea's reference moves the project's
  adoption row (instance -> adopted, variant -> variant). Withdrawing the
  shapes that gave an answer returns it to unassessed. This runs on
  classify_shapes, the sweep, confirm_proposals and the coverage refresh.
- assess and undo refuse an answer the shapes contradict. A conflict
  resolution re-judges the variant shapes on both sides.
- The proposer's family arm offers a canon idea's reference on a shared
  platform, in any language. It proposes only when the reference is the top
  hit over every readable snippet and scores at least 0.70. The pairs this
  was measured on are recorded beside _FAMILY_FLOOR. The proposer is now v6.
- The matrix cell shows the code that answers it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/services/coverage.py

@@ -879,6 +879,16 @@ async def compute_coverage(
         logger.warning("platform detection failed for project %s", project_id, exc_info=True)
 
     await shape_ledger.mark_canonicals(project_id, recorded)
+    # The adoption ledger follows the shapes (milestone 463 step 5). The
+    # judge paths sync the ideas they touch; the refresh is the one place
+    # that sees canonical stamps land and shapes vanish, so it answers every
+    # canon idea reaching the project. It must not fail the refresh.
+    try:
+        from scribe.services import family_adoption
+
+        await family_adoption.sync_from_shapes(user_id, project_id)
+    except Exception:
+        logger.warning("family adoption sync failed for project %s", project_id, exc_info=True)
     try:
         await shape_ledger.apply_derive_groups(project_id)
     except Exception:

src/scribe/services/family_adoption.py

@@ -43,13 +43,26 @@ applies wins, and every ground above it must be said not to:
 The losing side's reasoning is folded into the idea's note — as a trap, an
 alternative, or the branch for its condition — and is never dropped. The
 substance changed, so the version moves.
+
+SHAPES (step 5). The shape ledger answers too: a shape classified against an
+idea's reference — in any language — is the project's code saying `adopted`
+(an instance) or `variant` (with the shape's reason). The two ledgers never
+disagree: a classification moves the row, an assessment or undo the shapes
+contradict is refused, an answer the shapes gave is withdrawn with them, and
+a conflict resolution re-judges the variant shapes on both sides. The shape
+proposer offers an idea's reference across projects and languages by
+meaning; its rule and the measurement behind it sit above
+shape_ledger._FAMILY_FLOOR.
 """
 from __future__ import annotations
 
 import logging
+from typing import Iterable
+
 from sqlalchemy import func, select
 
 from scribe.models import async_session
+from scribe.models.code_shape import CodeShape
 from scribe.models.family import (
     FamilyAdoption, FamilyDecision, FamilyIdea, FamilyIdeaPlatform, FamilyIdeaReference,
     Platform, ProjectPlatform,
@@ -281,6 +294,224 @@ async def _project_languages(session, project_id: int) -> list[str]:
     return [r[0] for r in rows]
 
 
+# --- the shape ledger as evidence (milestone 463 step 5) ----------------------------
+#
+# A shape classified against an idea's reference IS an answer to the idea: an
+# `instance` — or the reference's own `canonical` location — says the project
+# does it; a `variant` says it departs, for the reason the shape carries. The
+# two ledgers must never disagree, and the shapes are the stronger evidence
+# (they name the code), so:
+#
+#   - classifying a shape moves the adoption row to what the shapes say,
+#     decided_via "system", the shapes as evidence;
+#   - an assessment or an undo that would contradict the shapes is refused —
+#     reclassify the shapes if they are wrong;
+#   - an answer the shape ledger gave is withdrawn to `unassessed` when the
+#     shapes that gave it are withdrawn. An answer given on other evidence is
+#     left alone: no shape is not the same as `owed`.
+
+SHAPE_SOURCE = "shape_ledger"
+_SHAPE_ADOPTS = ("canonical", "instance")
+
+# Which reference a shape is judged against when it is classified against an
+# idea: the one in the shape's language when there is one.
+_EXTS_BY_LANGUAGE = {
+    "python": (".py", ".pyi"), "go": (".go",), "kotlin": (".kt", ".kts"),
+    "java": (".java",), "dart": (".dart",), "swift": (".swift",), "rust": (".rs",),
+    "typescript": (".ts", ".tsx"), "javascript": (".js", ".jsx", ".mjs", ".cjs"),
+    "vue": (".vue",), "svelte": (".svelte",), "css": (".css",), "scss": (".scss",),
+    "bash": (".sh", ".bash"), "sh": (".sh",), "sql": (".sql",),
+}
+
+
+def path_speaks(path: str, language: str) -> bool:
+    """Is a file at ``path`` written in ``language`` (a snippet's recorded one)?"""
+    exts = _EXTS_BY_LANGUAGE.get((language or "").strip().lower())
+    return bool(exts) and (path or "").strip().lower().endswith(exts)
+
+
+def shape_outcome(statuses: Iterable[str]) -> str | None:
+    """What a project's shapes say about an idea: `adopted` when any shape is
+    an instance of (or is) a reference, `variant` when the only ones are
+    variants, None when no shape speaks. None is silence, never `owed`."""
+    seen = set(statuses)
+    if seen & set(_SHAPE_ADOPTS):
+        return "adopted"
+    if "variant" in seen:
+        return "variant"
+    return None
+
+
+def shapes_say(rows) -> dict | None:
+    """The answer a project's evidence rows give — outcome, reason, evidence
+    lines and the shapes themselves — or None when no shape speaks. The
+    `adopted` reason is fixed text, so classifying one more instance does not
+    log a new decision; a `variant` carries the first variant shape's why."""
+    outcome = shape_outcome(r.status for r in rows)
+    if outcome is None:
+        return None
+    speaking = [r for r in rows if (r.status in _SHAPE_ADOPTS) == (outcome == "adopted")]
+    if outcome == "adopted":
+        reason = "the shape ledger classifies this project's code as the idea's reference implementation"
+    else:
+        first = speaking[0]
+        reason = (f"the shape ledger classifies {first.path}::{first.symbol} as a variant "
+                  f"of #{first.snippet_id}: {(first.reason or '').strip()}")
+    return {
+        "outcome": outcome,
+        "reason": reason,
+        "evidence": [f"{r.path}::{r.symbol}" for r in speaking],
+        "shapes": [{"id": r.id, "path": r.path, "symbol": r.symbol, "status": r.status,
+                    "snippet_id": r.snippet_id} for r in speaking],
+    }
+
+
+async def _shape_evidence(session, project_id: int, idea_id: int) -> list[CodeShape]:
+    """The project's live shapes judged against any of the idea's references."""
+    refs = select(FamilyIdeaReference.snippet_id).where(FamilyIdeaReference.idea_id == idea_id)
+    return list((await session.execute(
+        select(CodeShape).where(
+            CodeShape.project_id == project_id,
+            CodeShape.vanished_at.is_(None),
+            CodeShape.snippet_id.in_(refs),
+            CodeShape.status.in_(_SHAPE_ADOPTS + ("variant",)),
+        ).order_by(CodeShape.path, CodeShape.symbol)
+    )).scalars().all())
+
+
+def _contradiction(outcome: str, said: dict | None, idea_id: int) -> str | None:
+    if said is None or outcome == said["outcome"]:
+        return None
+    named = ", ".join(said["evidence"][:3]) + (" …" if len(said["evidence"]) > 3 else "")
+    return (
+        f"the shape ledger already answers #{idea_id} in this project as {said['outcome']} "
+        f"({named}). The two ledgers never disagree: reclassify those shapes "
+        "(classify_shapes) if they are wrong, and the answer follows")
+
+
+async def reference_for(user_id: int, idea_id: int, path: str) -> int:
+    """The reference snippet a shape at ``path`` is judged against when it is
+    classified against a family idea: the one in the path's language when
+    there is one, else the first. An idea is shared across languages, so a
+    Python shape can be an instance of an idea whose only reference is Go.
+    Raises ValueError when the idea is not a family idea the caller can read
+    or has no reference they can read."""
+    if not await access.can_read_note(user_id, idea_id):
+        raise ValueError(f"#{idea_id} is not a family idea you can read")
+    async with async_session() as session:
+        if await session.get(FamilyIdea, idea_id) is None:
+            raise ValueError(f"#{idea_id} is not a family idea")
+        refs = await _references(session, idea_id)
+    readable = [r for r in refs if await access.can_read_note(user_id, r["id"])]
+    if not readable:
+        raise ValueError(
+            f"family idea #{idea_id} has no reference implementation you can read — "
+            "set_family_references first, or classify against a snippet_id")
+    for r in readable:
+        if path_speaks(path, r["language"]):
+            return r["id"]
+    return readable[0]["id"]
+
+
+async def family_reference_ids(project_id: int) -> set[int]:
+    """The reference snippets of every canon idea that reaches the project —
+    what the shape proposer may match across projects and languages."""
+    async with async_session() as session:
+        return set((await session.execute(
+            select(FamilyIdeaReference.snippet_id)
+            .join(FamilyIdea, FamilyIdea.note_id == FamilyIdeaReference.idea_id)
+            .join(FamilyIdeaPlatform, FamilyIdeaPlatform.note_id == FamilyIdea.note_id)
+            .join(ProjectPlatform, ProjectPlatform.platform_id == FamilyIdeaPlatform.platform_id)
+            .where(
+                FamilyIdea.status == "canon",
+                ProjectPlatform.project_id == project_id,
+                ProjectPlatform.state.in_(family_svc.MEMBER_STATES),
+            )
+        )).scalars().all())
+
+
+async def _latest_source(session, project_id: int, idea_id: int) -> str:
+    latest = (await session.execute(
+        select(FamilyDecision).where(
+            FamilyDecision.idea_id == idea_id, FamilyDecision.project_id == project_id)
+        .order_by(FamilyDecision.id.desc()).limit(1)
+    )).scalars().first()
+    return str(((latest.evidence if latest is not None else None) or {}).get("source") or "")
+
+
+async def _withdraw_shape_answer(user_id: int, project_id: int, idea_id: int) -> FamilyDecision:
+    reason = ("the shapes that answered this idea were withdrawn from the shape ledger; "
+              "it is unassessed again")
+    async with async_session() as session:
+        row = await _row(session, project_id, idea_id)
+        before = _row_state(row)
+        row.status = "unassessed"
+        row.reason = None
+        row.canon_version = None
+        row.assessed_at = None
+        row.decided_via = None
+        row.updated_at = family_svc._now()
+        decision = family_svc._log(
+            session, idea_id=idea_id, project_id=project_id, action="assess",
+            reason=reason, before=before, after=_row_state(row),
+            evidence={"source": SHAPE_SOURCE, "shapes": []}, precedent_ids=None,
+            decided_via="system", user_id=user_id,
+        )
+        await session.commit()
+        await session.refresh(decision)
+        row_id = row.id
+    await _sync_owed_task(user_id, row_id, reason=reason)
+    return decision
+
+
+async def sync_from_shapes(user_id: int, project_id: int,
+                           snippet_ids: Iterable[int] | None = None) -> list[dict]:
+    """Bring the project's adoption rows into line with its shape ledger, for
+    the canon ideas whose references are among ``snippet_ids`` — or every
+    canon idea that reaches the project when None (the coverage refresh,
+    which also sees shapes vanish).
+
+    A row that already gives the shapes' outcome at the current version is
+    left alone, whatever evidence it was given on. Returns one entry per
+    answer that moved: {idea_id, status, decision_id}."""
+    query = select(FamilyIdea.note_id).where(FamilyIdea.status == "canon")
+    if snippet_ids is not None:
+        wanted = {int(s) for s in snippet_ids if s}
+        if not wanted:
+            return []
+        query = query.where(FamilyIdea.note_id.in_(
+            select(FamilyIdeaReference.idea_id).where(FamilyIdeaReference.snippet_id.in_(wanted))))
+    async with async_session() as session:
+        idea_ids = [i for i in (await session.execute(query)).scalars().all()
+                    if await _is_member(session, project_id, i)]
+    moved: list[dict] = []
+    for idea_id in sorted(idea_ids):
+        if not await access.can_read_note(user_id, idea_id):
+            continue
+        async with async_session() as session:
+            idea = await session.get(FamilyIdea, idea_id)
+            said = shapes_say(await _shape_evidence(session, project_id, idea_id))
+            row = await _row(session, project_id, idea_id)
+            current = _row_state(row) if row is not None else None
+            source = await _latest_source(session, project_id, idea_id)
+        if said is not None:
+            if current and current["status"] == said["outcome"] \
+                    and current["canon_version"] == idea.canon_version:
+                continue
+            result = await assess(
+                user_id, project_id, idea_id, outcome=said["outcome"], reason=said["reason"],
+                evidence=said["evidence"], decided_via="system", source=SHAPE_SOURCE,
+                shapes=said["shapes"],
+            )
+            if result["changed"]:
+                moved.append({"idea_id": idea_id, "status": said["outcome"],
+                              "decision_id": result["decision"]["id"]})
+        elif current and current["status"] in ("adopted", "variant") and source == SHAPE_SOURCE:
+            decision = await _withdraw_shape_answer(user_id, project_id, idea_id)
+            moved.append({"idea_id": idea_id, "status": "unassessed", "decision_id": decision.id})
+    return moved
+
+
 async def assessment_precedents(user_id: int, project_id: int, idea_id: int,
                                 limit: int = 5) -> list[dict]:
     """What an assessment should be consistent with: the latest answer to
@@ -388,6 +619,20 @@ async def adoption_matrix(
                 select(Note).where(Note.id.in_(task_ids), Note.deleted_at.is_(None))
             )).scalars().all()
         } if task_ids else {}
+        # The code that answers each cell (step 5): live shapes classified
+        # against one of the idea's references.
+        evidence: dict[tuple[int, int], list[dict]] = {}
+        for iid, shape in (await session.execute(
+            select(FamilyIdeaReference.idea_id, CodeShape)
+            .join(CodeShape, CodeShape.snippet_id == FamilyIdeaReference.snippet_id)
+            .where(FamilyIdeaReference.idea_id.in_(idea_ids),
+                   CodeShape.project_id.in_(list(project_ids)),
+                   CodeShape.vanished_at.is_(None),
+                   CodeShape.status.in_(_SHAPE_ADOPTS + ("variant",)))
+            .order_by(CodeShape.path, CodeShape.symbol)
+        )).all() if idea_ids and project_ids else []:
+            evidence.setdefault((shape.project_id, iid), []).append(
+                {"path": shape.path, "symbol": shape.symbol, "status": shape.status})
 
     readable = [(pid, title) for pid, title in projects
                 if await access.can_read_project(user_id, pid)]
@@ -415,6 +660,7 @@ async def adoption_matrix(
                 "needs_recheck": bool(row) and needs_recheck(
                     row.status, row.canon_version, idea.status, idea.canon_version),
                 "owed_task": None,
+                "shapes": evidence.get((pid, iid), []),
             }
             task = tasks.get(row.owed_task_id) if row and row.owed_task_id else None
             if task is not None:
@@ -643,13 +889,17 @@ def _answer(row: FamilyAdoption, *, status: str, reason: str, version: int,
 async def assess(
     user_id: int, project_id: int, idea_id: int, *, outcome: str, reason: str,
     evidence: list[str] | None = None, precedent_ids: list[int] | None = None,
-    decided_via: str = "agent",
+    decided_via: str = "agent", source: str = "", shapes: list[dict] | None = None,
 ) -> dict:
     """Record one project's answer to one canon idea.
 
     Raises ValueError before writing anything when the answer is malformed
-    (assessment_problems), the caller cannot write the project, or the idea
-    is not canon or does not reach the project.
+    (assessment_problems), the caller cannot write the project, the idea
+    is not canon or does not reach the project, or the project's shape
+    ledger already answers the idea otherwise (the two never disagree).
+
+    ``source``/``shapes`` are the shape ledger's own door (sync_from_shapes):
+    the decision's evidence then names the shapes it was read from.
 
     The same answer given again — same outcome, reason and canon version —
     records nothing (`changed: False`); it still makes sure an owed answer
@@ -673,6 +923,11 @@ async def assess(
         if idea is None or idea.status != "canon":
             raise ValueError(f"#{idea_id} is not family canon — only canon is assessed")
         row = await _row_for_write(session, project_id, idea_id)
+        if source != SHAPE_SOURCE:
+            refused = _contradiction(
+                outcome, shapes_say(await _shape_evidence(session, project_id, idea_id)), idea_id)
+            if refused:
+                raise ValueError(refused)
         before = _row_state(row)
         after = {"status": outcome, "reason": reason.strip(), "canon_version": idea.canon_version}
         changed = before != after
@@ -683,8 +938,9 @@ async def assess(
             decision = family_svc._log(
                 session, idea_id=idea_id, project_id=project_id, action="assess",
                 reason=reason, before=before, after=_row_state(row),
-                evidence={"evidence": evidence}, precedent_ids=precedent_list,
-                decided_via=decided_via, user_id=user_id,
+                evidence=({"evidence": evidence, "source": source, "shapes": shapes or []}
+                          if source else {"evidence": evidence}),
+                precedent_ids=precedent_list, decided_via=decided_via, user_id=user_id,
             )
         await session.commit()
         if decision is not None:
@@ -722,6 +978,11 @@ async def undo_assessment(user_id: int, target: FamilyDecision, *, reason: str,
             raise ValueError(f"decision {target.id} cannot be undone: the answer it changed is gone")
         before = _row_state(row)
         prior = target.before or {"status": "unassessed", "reason": "", "canon_version": None}
+        refused = _contradiction(
+            prior["status"], shapes_say(await _shape_evidence(session, target.project_id, target.idea_id)),
+            target.idea_id)
+        if refused:
+            raise ValueError(f"decision {target.id} cannot be undone: {refused}")
         row.status = prior["status"]
         row.reason = (prior.get("reason") or "").strip() or None
         row.canon_version = prior.get("canon_version")
@@ -821,7 +1082,9 @@ async def resolve_conflict(
     the grounds checked above it); the canon side is answered `adopted`, and
     the other side `owed` (with a task filed) or, in a split, `adopted` under
     its condition. Each answer is its own `assess` decision, naming the
-    revision as its precedent.
+    revision as its precedent. Last, either side's shapes classified as a
+    variant of the idea are re-judged to agree with its new answer
+    (`shapes_rejudged`), so the shape ledger and this one do not disagree.
     """
     from scribe.services import notes as notes_svc
 
@@ -915,6 +1178,9 @@ async def resolve_conflict(
             row_ids[pid] = row.id
         await session.commit()
         await session.refresh(revision)
+    # The shapes follow the resolution, so the two ledgers still agree.
+    rejudged = {pid: await _shapes_follow(user_id, pid, idea_id, outcome, why)
+                for pid, outcome, why in answers}
     task = await _sync_owed_task(user_id, row_ids[other_project_id], reason=answers[1][2])
     await _sync_owed_task(user_id, row_ids[canon_project_id], reason=answers[0][2])
     return {
@@ -923,4 +1189,28 @@ async def resolve_conflict(
         "folded_as": g["fold_as"],
         "adoptions": await list_adoptions(user_id, idea_id=idea_id),
         "owed_task": task,
+        "shapes_rejudged": {str(pid): n for pid, n in rejudged.items() if n},
     }
+
+
+async def _shapes_follow(user_id: int, project_id: int, idea_id: int, outcome: str,
+                         why: str) -> int:
+    """Re-judge a project's variant shapes of the idea to agree with the
+    answer a conflict resolution just gave it: `adopted` makes them instances
+    of the reference they departed from (in a split, their condition is now
+    canon); `owed` returns them to the shape todo, to be rebuilt to the
+    canon the owed task names. Returns how many rows were re-judged."""
+    from scribe.services import shape_ledger
+
+    async with async_session() as session:
+        rows = [r for r in await _shape_evidence(session, project_id, idea_id)
+                if r.status == "variant"]
+    if not rows:
+        return 0
+    status = "instance" if outcome == "adopted" else "unclassified"
+    result = await shape_ledger.classify_shapes(user_id, project_id, [
+        {"path": r.path, "symbol": r.symbol, "kind": r.kind, "status": status,
+         "snippet_id": r.snippet_id, "reason": why}
+        for r in rows
+    ], via="agent")
+    return int(result.get("classified") or 0)

src/scribe/services/shape_ledger.py

@@ -514,7 +514,7 @@ def validate_classifications(items: list[dict]) -> str | None:
         snippet_id = item.get("snippet_id") or 0
         if status in _NEEDS_TARGET and not snippet_id:
             return (
-                f"classifications[{i}]: status {status!r} needs snippet_id — "
+                f"classifications[{i}]: status {status!r} needs snippet_id (or idea_id) — "
                 "the snippet this shape is (or departs from)"
             )
         if status in ("variant", "exempt") and not (item.get("reason") or "").strip():
@@ -570,6 +570,7 @@ async def classify_shapes(
 
     if via not in _CALLER_VIAS:
         raise ValueError(f"via must be one of: {', '.join(_CALLER_VIAS)}")
+    classifications = await _resolve_ideas(user_id, classifications)
     error = validate_classifications(classifications)
     if error:
         raise ValueError(error)
@@ -602,6 +603,7 @@ async def classify_shapes(
     classified = 0
     provisional = 0
     unmatched: list[dict] = []
+    touched: set[int] = set()
     async with async_session() as session:
         rows = (
             await session.execute(
@@ -639,6 +641,7 @@ async def classify_shapes(
                 continue
             status = item["status"]
             for row in matches:
+                touched.update(x for x in (row.snippet_id, item.get("snippet_id")) if x)
                 await _judge(
                     session, row, status=status,
                     snippet_id=int(item["snippet_id"]) if status in _NEEDS_TARGET else None,
@@ -653,9 +656,52 @@ async def classify_shapes(
     out = {"classified": classified, "unmatched": unmatched}
     if provisional:
         out["provisional"] = provisional
+    moved = await _sync_family(user_id, project_id, touched)
+    if moved:
+        out["family"] = moved
     return out
 
 
+async def _resolve_ideas(user_id: int, items: list[dict]) -> list[dict]:
+    """An item may name a family idea (`idea_id`) in place of a snippet
+    (milestone 463 step 5): it is judged against the idea's reference in the
+    shape's language, or its first when there is none in that language — an
+    idea is shared across languages. An explicit snippet_id wins."""
+    from scribe.services import family_adoption
+
+    out = []
+    for i, item in enumerate(items or []):
+        if (isinstance(item, dict) and item.get("idea_id") and not item.get("snippet_id")
+                and item.get("status") in _NEEDS_TARGET):
+            try:
+                sid = await family_adoption.reference_for(
+                    user_id, int(item["idea_id"]), (item.get("path") or "").strip())
+            except (TypeError, ValueError) as exc:
+                raise ValueError(f"classifications[{i}]: {exc}") from None
+            item = {**item, "snippet_id": sid}
+        out.append(item)
+    return out
+
+
+async def _sync_family(user_id: int, project_id: int, snippet_ids: set[int]) -> list[dict]:
+    """The adoption ledger follows the shapes (milestone 463 step 5): after a
+    judgment commits, the canon ideas whose references it touched — as the
+    new target or the one it replaced — are answered from the shapes.
+
+    A failure is logged and the judgment stands; the next judgment touching
+    those references, or the next coverage refresh, brings the two back in
+    line."""
+    from scribe.services import family_adoption
+
+    if not snippet_ids:
+        return []
+    try:
+        return await family_adoption.sync_from_shapes(user_id, project_id, snippet_ids)
+    except Exception:
+        logger.warning("family adoption sync failed for project %s", project_id, exc_info=True)
+        return []
+
+
 def rule_matches(row: CodeShape, *, path: str, pattern: str, kind: str) -> bool:
     """Does a ledger row fall under a rule-form classification (#2868)?
     ``path`` is a file or a directory (everything beneath it), ``pattern``
@@ -721,6 +767,7 @@ async def classify_shapes_where(
 
     now = datetime.now(timezone.utc)
     judged: list[str] = []
+    touched: set[int] = {int(snippet_id)} if snippet_id and status in _NEEDS_TARGET else set()
     async with async_session() as session:
         conds = [CodeShape.project_id == project_id, CodeShape.vanished_at.is_(None)]
         if not include_judged:
@@ -729,6 +776,8 @@ async def classify_shapes_where(
         for row in rows:
             if not rule_matches(row, path=path, pattern=pattern, kind=kind):
                 continue
+            if row.snippet_id:
+                touched.add(row.snippet_id)
             await _judge(
                 session, row, status=status,
                 snippet_id=int(snippet_id) if status in _NEEDS_TARGET else None,
@@ -738,7 +787,11 @@ async def classify_shapes_where(
                 await record_uses(session, row, uses, basis=via, evidence=reason)
             judged.append(f"{row.path}::{row.symbol}")
         await session.commit()
-    return {"classified": len(judged), "sample": sorted(judged)[:12]}
+    out = {"classified": len(judged), "sample": sorted(judged)[:12]}
+    moved = await _sync_family(user_id, project_id, touched)
+    if moved:
+        out["family"] = moved
+    return out
 
 
 async def list_project_shapes(
@@ -1611,6 +1664,29 @@ _SEMANTIC_LIMIT = 8
 # against a prose-forward snippet document measures the wrong field (#2518);
 # no floor separates the two bands. The arm PROPOSES on a hit; its silence
 # says nothing.
+#
+# THE FAMILY ARM (milestone 463 step 5). The arm above is held to the shape's
+# own project and language family, because across projects it was pure noise
+# (#2871). A family idea is the exception the hold was waiting for: an idea
+# shared across projects ON PURPOSE, whose reference may be in another
+# language (a Python throttle is an instance of a Go one). So the arm also
+# proposes the reference of a canon idea that reaches the shape's project
+# through a shared platform — any language, any project — under a stricter
+# rule of its own, measured 2026-10-06 (#4991) on cross-project pairs:
+#
+#   true pairs   A py→go 0.728 (next 0.703)   B py→go 0.715 (next 0.675)
+#                D kt→kt 0.816 (next 0.734)   E go→go 0.610 (next 0.604)
+#   no reference N1 0.666  N2 0.623  N3 0.626  N4 0.715  N5 0.614 (best hit,
+#                none of them a family reference); unrelated hits to 0.774
+#
+# No floor separates those bands — the false band reaches 0.715–0.774, a
+# true pair sits at 0.610. RANK does: every true pair was the single best
+# snippet the user can read. So a family reference is proposed only when it
+# is the TOP hit over everything readable (not merely the first allowed one,
+# as above) and clears _FAMILY_FLOOR: A, B, D proposed; E missed; no
+# negative proposed. A miss is still not evidence — the judge can classify
+# against the idea by idea_id.
+_FAMILY_FLOOR = 0.70
 
 
 def _semantic_priority(row) -> tuple:
@@ -1640,7 +1716,9 @@ def _semantic_priority(row) -> tuple:
 # v5: the semantic arm's floor dropped from 0.8 to the write-path floor (#4208),
 # and the signature floor from 0.8 to 0.75 (#4306), so rows examined and
 # found nothing for must be read once more.
-_PROPOSER_VERSION = 5
+# v6: the family arm (milestone 463 step 5) — a canon idea's reference on a
+# shared platform, any language, as the top hit at _FAMILY_FLOOR.
+_PROPOSER_VERSION = 6
 # Signature resemblance floor, name blanked (difflib ratio) — and a length
 # floor, because `def NAME():` resembles `def NAME(x):` at 0.95 while saying
 # nothing; a family shape has parameters to resemble.
@@ -1883,28 +1961,47 @@ def _substance(text: str) -> int:
     return len("".join((text or "").split()))
 
 
+def pick_semantic(
+    hits: list[tuple[float, int]], allowed: set[int], family: set[int], *, floor: float,
+) -> tuple[int, float, str] | None:
+    """Which ranked hit the semantic arm proposes, as (snippet_id, score,
+    basis). Pure; ``hits`` are (score, snippet_id) over everything the user
+    can read, best first. The TOP hit may be a family reference (basis
+    "family", at _FAMILY_FLOOR); any hit at ``floor`` may be an own-project
+    canon (basis "semantic")."""
+    for rank, (score, sid) in enumerate(hits):
+        if rank == 0 and sid in family and score >= _FAMILY_FLOOR:
+            return sid, round(float(score), 3), "family"
+        if sid in allowed and score >= floor:
+            return sid, round(float(score), 3), "semantic"
+    return None
+
+
 async def _semantic_canon(
-    user_id: int, body: str, allowed: set[int],
-) -> tuple[int, float] | None:
-    """The canon this body MEANS, or None. None is "no proposal", never "not
-    the canon" — see the note above `_SEMANTIC_LIMIT`."""
+    user_id: int, body: str, allowed: set[int], family: set[int] | None = None,
+) -> tuple[int, float, str] | None:
+    """The canon this body MEANS, as (snippet_id, score, basis), or None.
+    None is "no proposal", never "not the canon" — see the note above
+    `_SEMANTIC_LIMIT`; the family arm's rule is the note above
+    `_FAMILY_FLOOR`."""
     from scribe.services.embeddings import semantic_search_notes
     from scribe.services.plugin_context import (
         WRITEPATH_DEFAULT_THRESHOLD, WRITEPATH_MIN_CODE_CHARS, concept_query,
     )
 
-    if _substance(body) < WRITEPATH_MIN_CODE_CHARS or not allowed:
+    family = family or set()
+    if _substance(body) < WRITEPATH_MIN_CODE_CHARS or not (allowed or family):
         return None
     query = concept_query(body) or body
     hits = await semantic_search_notes(
         user_id, query, limit=_SEMANTIC_LIMIT,
-        threshold=WRITEPATH_DEFAULT_THRESHOLD,
+        threshold=min(WRITEPATH_DEFAULT_THRESHOLD, _FAMILY_FLOOR),
         note_type="snippet", scope="browse",
     )
-    for score, note in hits:
-        if int(note.id) in allowed:
-            return int(note.id), round(float(score), 3)
-    return None
+    return pick_semantic(
+        [(float(score), int(note.id)) for score, note in hits], allowed, family,
+        floor=WRITEPATH_DEFAULT_THRESHOLD,
+    )
 
 
 async def propose_for_repo(
@@ -1933,6 +2030,16 @@ async def propose_for_repo(
 
     def semantic_allowed(path: str) -> set[int]:
         return {c.snippet_id for c in sym_canons if same_family(path, c.language)}
+    # The family arm: references of canon ideas on a platform this project
+    # shares, in any language (see _FAMILY_FLOOR). A project on no shared
+    # platform gets none, so nothing is proposed across to it.
+    try:
+        from scribe.services import family_adoption
+
+        family_refs = await family_adoption.family_reference_ids(project_id)
+    except Exception:
+        logger.warning("family references unreadable for project %s", project_id, exc_info=True)
+        family_refs = set()
     now = datetime.now(timezone.utc)
     examined = proposed = checked = 0
     async with async_session() as session:
@@ -1998,13 +2105,13 @@ async def propose_for_repo(
                 continue
             checked += 1
             try:
-                found = await _semantic_canon(user_id, d[5], semantic_allowed(row.path))
+                found = await _semantic_canon(
+                    user_id, d[5], semantic_allowed(row.path), family_refs)
             except Exception:
                 logger.warning("semantic proposal failed", exc_info=True)
                 found = None
             if found:
-                row.proposed_snippet_id, row.proposal_score = found
-                row.proposal_basis = "semantic"
+                row.proposed_snippet_id, row.proposal_score, row.proposal_basis = found
                 row.proposal_group = None
                 proposed += 1
         await session.commit()
@@ -2210,11 +2317,13 @@ async def confirm_proposals(
         conds.append(CodeShape.proposal_basis == basis.strip())
     now = datetime.now(timezone.utc)
     confirmed = 0
+    touched: set[int] = set()
     async with async_session() as session:
         rows = (await session.execute(select(CodeShape).where(*conds))).scalars().all()
         for row in rows:
             if (row.proposal_score or 0.0) < min_score:
                 continue
+            touched.add(row.proposed_snippet_id)
             await _judge(
                 session, row, status="instance", snippet_id=row.proposed_snippet_id,
                 by="agent", at=now,
@@ -2225,7 +2334,11 @@ async def confirm_proposals(
             )
             confirmed += 1
         await session.commit()
-    return {"confirmed": confirmed}
+    out = {"confirmed": confirmed}
+    moved = await _sync_family(user_id, project_id, touched)
+    if moved:
+        out["family"] = moved
+    return out
 
 
 # --- the divergence readout (#2793): button B where button A is canon -------