docs(6209): twelve more test files say which behaviour they pin

shape ledger, MCP projects/search/rulebooks tools, backup, chunking,
plugin context, derived mirror, rule band, shape form gate, plugin
version mint and note usage tests drop issue, milestone and rule numbers,
dates and one-install figures from docstrings, comments and messages.
Three shape-form-gate test names that told the discovery story now name
the property: a registry module's helpers are not service functions, the
divergence gate silences only a family contradiction, and callable helpers
beside a callable canon still prompt. The rulebook tool-count comment that
logged each milestone's additions is replaced by the reason it is a count.

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

tests/test_mcp_tool_rulebooks.py

@@ -49,8 +49,7 @@ async def test_get_rulebook_raises_when_not_found():
             await get_rulebook(rulebook_id=999)
 
 
-# _plain_detail moved to tests/helpers on its second copy (#2825's own
-# reason for existing): two stubs for one seam drift apart quietly, and a
+# _plain_detail lives in tests/helpers: two stubs for one seam drift apart quietly, and a
 # test stubbing it slightly differently asserts something slightly different
 # than it appears to.
 
@@ -199,16 +198,7 @@ def test_register_attaches_every_tool():
     mcp = FakeMCP()
 
     register(mcp)
-    # 26 through milestone 307, +2 for the staleness sweep (milestone 312),
-    # +1 for a rule's edit history (milestone 323), +2 for preferences
-    # (milestone 399).
-    # 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. 23 with move_rule
-    # (milestone 414 step 3), the way a rule changes home. 24 with
-    # rule_outcome (milestone 419 step 1), the way a rule says what it
-    # actually changed.
+    # Pinned as a count so a tool added or dropped is a deliberate edit here.
     assert len(mcp.names) == 24
     # spot-check a few names
     assert "list_rulebooks" in mcp.names
@@ -221,12 +211,12 @@ def test_register_attaches_every_tool():
     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
+    # the sweep, and the stamp that answers it
     assert "rules_due_for_verification" in mcp.names
     assert "mark_rule_verified" in mcp.names
-    # milestone 323: what a rule used to say
+    # what a rule used to say
     assert "rule_history" in mcp.names
-    # milestone 414: a rule's home is its scope; nothing subscribes or mutes.
+    # a rule's home is its scope; nothing subscribes or mutes.
     for gone in ("subscribe_project_to_rulebook", "unsubscribe_project_from_rulebook",
                  "suppress_rule_for_project", "unsuppress_rule_for_project",
                  "suppress_topic_for_project", "unsuppress_topic_for_project"):
@@ -292,7 +282,7 @@ async def test_create_project_rule_uses_explicit_title_when_given():
     assert kwargs["title"] == "no auto-docstrings"
 
 
-# ── Typed edges between rules (milestone 307) ───────────────────────────
+# ── Typed edges between rules ───────────────────────────────────────────
 
 @pytest.mark.asyncio
 async def test_relate_rules_forwards_the_kind_and_the_why():
@@ -336,7 +326,7 @@ async def test_unrelate_rules_raises_when_the_edge_is_gone():
             await unrelate_rules(relation_id=99)
 
 
-# ── rule_history (milestone 323 step 3) ────────────────────────────────
+# ── rule_history ───────────────────────────────────────────────────────
 
 def _fake_version(**over):
     """A RuleVersion-shaped stand-in. A real model instance rather than a
@@ -397,9 +387,8 @@ async def test_rule_history_opens_one_version_in_full():
 
 @pytest.mark.asyncio
 async def test_rule_history_says_an_empty_history_is_ordinary():
-    """Most rules have never been reworded, and nothing was written before
-    milestone 323. Without this line an empty list reads as a lost history or
-    a broken tool."""
+    """Most rules have never been reworded. Without this line an empty list
+    reads as a lost history or a broken tool."""
     with patch(
         "scribe.mcp.tools.rulebooks.rulebooks_svc.list_rule_versions",
         AsyncMock(return_value=[]),
@@ -482,7 +471,7 @@ async def test_move_rule_on_someone_elses_rule_is_not_found():
             await move_rule(rule_id=94, project_id=3)
 
 
-# ── rule_outcome: what a rule actually changed (#4212, milestone 419) ─────
+# ── rule_outcome: what a rule actually changed ───────────────────────────
 
 @pytest.mark.asyncio
 async def test_rule_outcome_records_an_application():