fix(retrieval): the place arm marks its repeats too, and three tests meet the new contract (#4101)

CI on 5c64ea0 surfaced a half-measure I had shipped and three tests pinning the
semantics it replaces.

**The half-measure.** Only the semantic arm was marking repeats; the write
path's PLACE arm still dropped a nearby snippet that was on the ledger. One
menu, two rules, decided by which arm happened to find a record — and the
marker would then read as a complete account of what the session has met while
covering half the lines. `seen` now means this call's own menu and nothing
else, so both reuse arms mark and neither withholds.

**test_session_dedup_excludes_ids_from_the_reuse_arms** asserted the drop and
the ledger going into the query. Both are the defect; it is renamed and asserts
the marker instead.

**test_a_pulled_snippet_already_seen_is_evidence_not_menu** asserted #7 was
evidence and NOT menu, with the limit widened by one to pay for the drop. The
premise was the hard exclusion; #7 is now both, and the widening is no longer
needed for it.

**test_a_record_this_arm_withheld_itself_is_not_a_near_miss** is the
interesting one. Its property still holds and its setup no longer reaches it:
a ledger repeat comes back from the search and is rendered, so nothing is
withheld and `best_available` describes the bar. The one post-search filter
left is a PULLED record this same call already listed by place — kept in the
query because `resembles` needs its score, dropped from the menu because it is
already on it — so the test is rebuilt on that, and a sibling test pins the
direction that changed, so nulling the score whenever the ledger matches
cannot pass both.

Also stubs `superseded_ids` and `owner_names_for` in the new test file, which
were reaching for Postgres in a unit job.

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

tests/test_ledger_references_not_silence.py

@@ -77,7 +77,9 @@ async def _autoinject(hits, exclude_ids, *, rec=None, surf=None):
             return_value={"enabled": True, "threshold": 0.55, "top_k": 3})), \
          patch.object(pc, "semantic_search_notes", search), \
          patch.object(pc, "record_retrieval", rec or MagicMock()), \
-         patch.object(pc, "record_surfaced", surf or MagicMock()):
+         patch.object(pc, "record_surfaced", surf or MagicMock()), \
+         patch.object(pc, "owner_names_for", AsyncMock(return_value={})), \
+         patch.object(pc, "superseded_ids", AsyncMock(return_value=set())):
         out = await pc.build_autoinject_hint(
             1, "postgres pool", project_id=2, exclude_ids=exclude_ids)
     return out, search
@@ -175,7 +177,8 @@ async def _write_path(hits, exclude_ids, *, here=(), rec=None, sync_exclude=()):
          patch.object(pc.snippets_svc, "list_snippets", listing), \
          patch.object(pc, "semantic_search_notes", search), \
          patch.object(pc, "record_retrieval", rec or MagicMock()), \
-         patch.object(pc, "record_surfaced", MagicMock()):
+         patch.object(pc, "record_surfaced", MagicMock()), \
+         patch.object(pc, "owner_names_for", AsyncMock(return_value={})):
         out = await pc.build_write_path_hint(
             1, "src/x.py", code=REAL_CODE,
             exclude_ids=list(exclude_ids),