fix(planning): the plan gate joins step text through embedding_text (#4079)

test_nothing_else_builds_the_embedding_document_itself caught start_planning
building f"{title}\n{body}" inline for the plan gate's candidate text. That is
the embedded-document shape; plan_candidate_text now takes (title, body) pairs
and calls embedding_text, so the candidate moves with the corpus it is ranked
against (#2486).

Also carries the create_task / create_records milestone_id docstring lines from
step 5 (#4080), which share the file.

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

src/scribe/mcp/tools/tasks.py

@@ -152,6 +152,9 @@ async def create_task(
         priority: One of: low, medium, high, or 'none'. Omit (empty string) to leave unset.
         project_id: Associate with a project (0 = no project).
         milestone_id: Place within a project milestone (0 = no milestone).
+            When the work belongs to an active plan — a milestone in
+            enter_project's lists or found by search(content_type=
+            "milestone") — pass its id, so the plan shows all of its work.
         parent_id: Make this a sub-task of another task (0 = top-level).
         tags: List of plain-string tags without # prefix.
         kind: 'work' (default), 'issue', or 'spike'.
@@ -462,6 +465,8 @@ async def create_records(
         project_id: The project every record belongs to (0 = none, or taken
             from milestone_id).
         milestone_id: File every record under this existing milestone (0 = none).
+            This is how steps are added to a plan that already exists,
+            including one start_planning handed back as `existing_milestone`.
         force: Bypass the near-duplicate gate for the whole batch. By default
             the first record that near-duplicates an existing one BLOCKS the
             batch, and its existing id comes back so you can update it instead.
@@ -553,7 +558,7 @@ async def start_planning(
         match = await dedup_svc.plan_gate(
             uid, project_id, title,
             dedup_svc.plan_candidate_text(
-                body=body, step_texts=[f"{i.title}\n{i.body or ''}" for i in items],
+                body=body, steps=[(i.title, i.body) for i in items],
             ),
         )
         if match is not None: