feat(family): an idea links to the rule topic holding its norms - set_family_topic, the readouts name the rules, the idea row shows the link (milestone 463 step 1 gap, found in step 7, #4993)

Step 1 added family_ideas.topic_id but nothing could set it, so the note<->topic
link the milestone promised existed only as a column. set_family_topic links or
unlinks (0) a topic in a rulebook the caller owns, one idea per topic; the
version does not move. get_family_idea and get_family_adoption list the topic's
rules; list_family_ideas and the Family page name the topic. The model
docstrings no longer claim the topic's rules are platform-scoped in retrieval.

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

tests/test_integration_family_promotion.py

@@ -11,6 +11,7 @@ test here (`_no_meaning`); the repeat tests stub it to one hit, to pin what
 the trigger does WITH a hit. The ranking itself is the shared semantic
 search, tested where that lives.
 """
+import uuid
 from unittest.mock import AsyncMock, patch
 
 import pytest
@@ -24,6 +25,7 @@ from scribe.models.family import (
 from scribe.models.milestone import Milestone
 from scribe.models.note import Note
 from scribe.models.project import Project
+from scribe.models.rulebook import Rule, Rulebook, RulebookTopic
 from scribe.models.user import User
 from scribe.services import family as family_svc
 from tests.helpers import ensure_user
@@ -291,3 +293,86 @@ async def test_a_milestone_closing_on_a_platform_asks_and_one_off_platform_does_
     assert hint and "Android app" in hint
     assert await family_svc.milestone_trigger(family["owner"], off_platform) is None
     assert await family_svc.milestone_is_open(family["owner"], on_platform.id) is True
+
+
+# --- the note↔topic link ----------------------------------------------------------
+
+@pytest_asyncio.fixture
+async def topics(family):
+    """A topic of the owner's with two rules, a second empty one, and one in
+    the outsider's rulebook. Titles carry a nonce: rulebooks are not purged
+    with the notes, and a topic's title is unique within its rulebook."""
+    nonce = uuid.uuid4().hex[:8]
+    async with async_session() as s:
+        mine = Rulebook(owner_user_id=family["owner"], title=f"family norms {nonce}")
+        theirs = Rulebook(owner_user_id=family["outsider"], title=f"their norms {nonce}")
+        s.add_all([mine, theirs])
+        await s.flush()
+        norms = RulebookTopic(rulebook_id=mine.id, title="distribution")
+        spare = RulebookTopic(rulebook_id=mine.id, title="spare")
+        foreign = RulebookTopic(rulebook_id=theirs.id, title="theirs")
+        s.add_all([norms, spare, foreign])
+        await s.flush()
+        s.add_all([
+            Rule(topic_id=norms.id, title="One release key", statement="Sign with one key.",
+                 order_index=0),
+            Rule(topic_id=norms.id, title="No debug signer", statement="Check the signer.",
+                 order_index=1),
+        ])
+        await s.commit()
+        return {"norms": norms.id, "spare": spare.id, "foreign": foreign.id,
+                "rulebook": mine.id}
+
+
+async def test_an_idea_links_to_its_topic_and_its_reads_name_the_rules(family, topics):
+    await _promote(family)
+    out = await family_svc.set_topic(family["owner"], family["note"], topics["norms"])
+    assert out["topic_id"] == topics["norms"]
+    assert [r["title"] for r in out["topic"]["rules"]] == ["One release key", "No debug signer"]
+    # Where the norms are found is not what they say: the version holds.
+    assert out["canon_version"] == 1
+
+    idea = await family_svc.get_idea(family["owner"], family["note"])
+    assert idea["topic"]["rulebook_id"] == topics["rulebook"]
+    assert len(idea["topic"]["rules"]) == 2
+    [listed] = [i for i in await family_svc.list_ideas(family["owner"])
+                if i["note_id"] == family["note"]]
+    assert listed["topic"] == {"id": topics["norms"], "title": "distribution",
+                               "rulebook_id": topics["rulebook"]}
+
+
+async def test_zero_unlinks_the_topic(family, topics):
+    await _promote(family)
+    await family_svc.set_topic(family["owner"], family["note"], topics["norms"])
+    out = await family_svc.set_topic(family["owner"], family["note"], 0)
+    assert out["topic_id"] is None and out["topic"] is None
+
+
+async def test_a_topic_outside_the_callers_rulebooks_is_refused(family, topics):
+    await _promote(family)
+    with pytest.raises(ValueError, match="rulebook you own"):
+        await family_svc.set_topic(family["owner"], family["note"], topics["foreign"])
+    assert (await _idea(family["note"])).topic_id is None
+
+
+async def test_one_topic_carries_one_ideas_norms(family, topics):
+    await _promote(family)
+    await family_svc.set_topic(family["owner"], family["note"], topics["norms"])
+    async with async_session() as s:
+        other = Note(user_id=family["owner"], project_id=family["b"], title="Another idea",
+                     body="something else every Android app needs")
+        s.add(other)
+        await s.flush()
+        s.add(FamilyIdea(note_id=other.id, status="candidate"))
+        await s.commit()
+        other_id = other.id
+    with pytest.raises(ValueError, match="already carries the norms"):
+        await family_svc.set_topic(family["owner"], other_id, topics["norms"])
+    # Re-linking the same idea to its own topic is not a conflict.
+    await family_svc.set_topic(family["owner"], family["note"], topics["norms"])
+
+
+async def test_someone_who_cannot_write_the_idea_cannot_link_it(family, topics):
+    await _promote(family)
+    with pytest.raises(ValueError, match="no write access"):
+        await family_svc.set_topic(family["outsider"], family["note"], topics["spare"])