feat(dedup): a note or task blocks only as a copy; a close match is surfaced for judgement (#4306)

Measured on the live corpus, the 74 note pairs at or above the old 0.90 bar
were almost all distinct siblings — consecutive dev-logs, sub-notes of one
design, research parts — and the one clear copy sat at 0.997. The block
refused the next dev-log and taught force=true, as #4134 found for rules.

- The semantic arm blocks notes and tasks only at >= 0.98. The title block
  stays; processes keep 0.90 (not measured).
- 0.87 to 0.98 comes back as `overlaps` on the create reply, from the same
  per-chunk searches, with a note that leaves the call to the session:
  fold in and delete if it is the same record, keep both if a sibling.
- create_note, create_task, create_records and start_planning's steps all
  carry it; a batch names the record each overlap belongs to.

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

src/scribe/mcp/tools/tasks.py

@@ -304,10 +304,14 @@ async def create_task(
         arose_from_id: For an issue, the id of the task/feature it arose from;
             for a spike, the record that raised the question — including a
             standing rule whose check just failed. 0 = none.
-        force: Bypass the near-duplicate gate. By default, if a title- or
-            meaning-similar task already exists in the same project, creation is
-            BLOCKED and the existing task's id is returned so you update it
-            instead. Set true only for a genuinely distinct task.
+        force: Bypass the near-duplicate gate. By default, a task with the
+            same title, or one that reads as a copy, in the same project BLOCKS
+            the create and its id is returned so you update it instead. A task
+            that reads CLOSE but not identical does not block: the task is
+            created and the reply carries `overlaps` — open the top one and
+            judge whether it is the same work (fold in, delete the new one) or
+            separate work (keep both). Set force true only when a blocked task
+            is genuinely distinct.
 
     AN ID EXISTS ONLY ONCE A CREATE RETURNS IT. Never write the id you expect
     a record to get: every session and user draws from one sequence, so the
@@ -332,10 +336,11 @@ async def create_task(
             "task with create_task(milestone_id=<that milestone>)."
         )
     await refuse_guessed_ids(title, body)
+    overlaps: list = []
     if not force:
         dup = await dedup_svc.find_duplicate_note(
             uid, title, body, project_id=project_id or None,
-            is_task=True, note_type="note",
+            is_task=True, note_type="note", overlaps=overlaps,
         )
         if dup is not None:
             return dedup_svc.duplicate_response(dup, "task")
@@ -356,6 +361,7 @@ async def create_task(
         await systems_svc.set_record_systems(uid, note.id, system_ids)
     data = note.to_dict()
     await systems_tools.attach_systems(uid, uid, data, note.id, project_id or None)
+    data.update(dedup_svc.note_overlap_response(overlaps, "task"))
     return await placement_svc.attach_placement(uid, data, note)
 
 
@@ -556,13 +562,23 @@ def _batch_items(records: list[dict], *, what: str = "record") -> list[batch_svc
     return items
 
 
-async def _first_duplicate(uid: int, items: list, project_id: int | None) -> dict | None:
-    """The duplicate gate over a whole batch — the first hit blocks all of it."""
+async def _first_duplicate(
+    uid: int, items: list, project_id: int | None,
+    overlaps: dict | None = None,
+) -> dict | None:
+    """The duplicate gate over a whole batch — the first hit blocks all of it.
+
+    `overlaps`, when given, collects each record's near matches below the copy
+    band by its 1-based position (#4306), for the reply once the batch is
+    created."""
     for i, item in enumerate(items, start=1):
+        found: list = []
         dup = await dedup_svc.find_duplicate_note(
             uid, item.title, item.body, project_id=project_id,
-            is_task=item.is_task, note_type="note",
+            is_task=item.is_task, note_type="note", overlaps=found,
         )
+        if found and overlaps is not None:
+            overlaps[i] = found
         if dup is not None:
             payload = dedup_svc.duplicate_response(dup, "task" if item.is_task else "note")
             payload["record"] = i
@@ -616,14 +632,17 @@ async def create_records(
     uid = current_user_id()
     items = _batch_items(records)
     await refuse_guessed_ids(*[t for item in items for t in (item.title, item.body)])
+    overlaps: dict = {}
     if not force:
-        dup = await _first_duplicate(uid, items, project_id or None)
+        dup = await _first_duplicate(uid, items, project_id or None, overlaps)
         if dup is not None:
             return dup
     _ms, notes = await batch_svc.create_batch(
         uid, items, project_id=project_id or None, milestone_id=milestone_id or None,
     )
-    return {"ids": [n.id for n in notes], "records": [n.to_dict() for n in notes]}
+    out = {"ids": [n.id for n in notes], "records": [n.to_dict() for n in notes]}
+    out.update(dedup_svc.batch_overlap_response(overlaps))
+    return out
 
 
 async def start_planning(
@@ -699,14 +718,18 @@ async def start_planning(
         )
         if match is not None:
             return match
+    overlaps: dict = {}
     if items and not force:
-        dup = await _first_duplicate(uid, items, project_id or None)
+        dup = await _first_duplicate(uid, items, project_id or None, overlaps)
         if dup is not None:
             return dup
-    return await planning_svc.start_planning(
+    result = await planning_svc.start_planning(
         user_id=uid, project_id=project_id, title=title,
         body=body or None, steps=items or None,
     )
+    if isinstance(result, dict):
+        result.update(dedup_svc.batch_overlap_response(overlaps))
+    return result
 
 
 async def delete_task(task_id: int) -> dict: