feat(rules): move a rule between global and project scope, keeping its id, history, areas and edges (#4063)

A rule's home is its reach: a rulebook topic makes it global, a project makes it
that project's. There was no way to change one, so a project rule decided to be
global could only be recreated and the original trashed — losing the id every
record cites, its edit history, its area tags and its relations.

- services.rulebooks.move_rule(rule_id, user_id, topic_id= | project_id=):
  exactly one destination (the model's CHECK), owned by the caller, not the
  rule's current home. A topic already holding a live rule with the same title
  is refused with a message naming that rule, instead of uq_rule_per_topic
  failing the commit. Someone else's rule reads as not found.
- Deliberately NOT done, and said in the docstring: no version (a version is
  what a rule said, milestone 323 decision 4), no duplicate gate (nothing new
  enters the corpus), no re-embed (retrieval reads the home at query time).
- Both doors: MCP move_rule, REST POST /api/rules/<id>/move (rule 33).
- UI: RuleHomePicker, one component in the rule editor (a global rule) and a
  project's rules tab (a project rule), so the two cannot drift on what a
  destination is.
- using-scribe names move_rule under "Where a new rule goes". Plugin
  2026.09.15.1626.

Milestone 414 step 3.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

tests/test_mcp_tool_rulebooks.py

@@ -204,8 +204,9 @@ def test_register_attaches_every_tool():
     # 28 since milestone 394 took list_always_on_rules and the two
     # always-on exclusion tools with the tier they served.
     # 22 since milestone 414 retired subscriptions and suppressions: the two
-    # subscribe tools and the four suppress/unsuppress tools.
-    assert len(mcp.names) == 22
+    # subscribe tools and the four suppress/unsuppress tools. 23 with move_rule
+    # (milestone 414 step 3), the way a rule changes home.
+    assert len(mcp.names) == 23
     # spot-check a few names
     assert "list_rulebooks" in mcp.names
     assert "create_rule" in mcp.names
@@ -216,6 +217,7 @@ def test_register_attaches_every_tool():
     assert "create_preference" in mcp.names
     assert "update_preference" in mcp.names
     assert "create_project_rule" in mcp.names
+    assert "move_rule" in mcp.names
     # milestone 312: the sweep, and the stamp that answers it
     assert "rules_due_for_verification" in mcp.names
     assert "mark_rule_verified" in mcp.names
@@ -448,3 +450,27 @@ def test_rule_history_docstring_says_what_a_version_HOLDS():
         "and, not finding it, is likely to hand-copy the old text back with "
         "no record of why."
     )
+
+
+@pytest.mark.asyncio
+async def test_move_rule_passes_one_destination_and_returns_the_detail():
+    """The tool is a thin door: the service decides what a valid move is, and
+    the reply is the same rule_detail every other write returns."""
+    moved = fake_rule(id=94, topic_id=12, project_id=None)
+    move = AsyncMock(return_value=moved)
+    detail = AsyncMock(return_value={"id": 94, "topic_id": 12, "project_id": None})
+    with patch("scribe.mcp.tools.rulebooks.rulebooks_svc.move_rule", move), \
+         patch("scribe.mcp.tools.rulebooks.rulebooks_svc.rule_detail", detail):
+        from scribe.mcp.tools.rulebooks import move_rule
+        out = await move_rule(rule_id=94, topic_id=12)
+    assert move.await_args.args[0] == 94
+    assert move.await_args.kwargs == {"topic_id": 12, "project_id": 0}
+    assert out["topic_id"] == 12
+
+
+@pytest.mark.asyncio
+async def test_move_rule_on_someone_elses_rule_is_not_found():
+    with patch("scribe.mcp.tools.rulebooks.rulebooks_svc.move_rule", AsyncMock(return_value=None)):
+        from scribe.mcp.tools.rulebooks import move_rule
+        with pytest.raises(ValueError, match="not found"):
+            await move_rule(rule_id=94, project_id=3)