fix(ledger): the in-play tuple widened and one consumer kept reading four (#4204)

[s_id for rank, _at, s_id, _why in bucket if rank == 2]
    ValueError: too many values to unpack (expected 4, got 5)

`in_play` gained the canon's form as a fifth element so the stamp could be
decided per shape rather than per file. The `record_uses` call eighty lines
below still destructured four, and every stamp that reached it raised.

Both integration failures on runs 7090 and 7091 are this one line —
`test_write_path_stamp_is_evidence_that_yields_to_judgment` and
`test_a_brand_new_shape_gets_a_provisional_row_the_sync_settles`.

Now indexed rather than destructured, matching the candidate scan above it, so
the next widening cannot break it positionally.

WHY THE UNIT LANE STAYED GREEN THROUGH TWO PUSHES. `record_uses` is only
reached once a stamp is actually written, which needs a real snippet, a real
ledger row and the write ACL — so no unit test crosses that line. 139 local
assertions and the whole unit suite passed on code that raised on every
successful stamp. The integration lane was the only thing that could say so,
which is the case for it.

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

src/scribe/services/shape_ledger.py

@@ -1290,7 +1290,12 @@ async def stamp_write_path_instances(
             # call-site fact, independent of which one the row is judged to be.
             await record_uses(
                 session, row,
-                [s_id for rank, _at, s_id, _why in bucket if rank == 2],
+                # Indexed, not destructured: this list widened from 4 to 5 when
+                # the canon's form joined it (#4204) and a positional unpack
+                # here went on reading four. The unit lane never touches
+                # `record_uses`, so it stayed green and the integration lane
+                # was the only thing that said so.
+                [t[2] for t in bucket if t[0] == 2],
                 basis="hook", evidence="write path: pulled the snippet, payload names its symbol",
             )
         if stamped: