docs(bf-1ccqa): post Mode A partitioning coverage close-out comments

Step-4 close-out of the Mode A partitioning coverage investigation
(umbrella bf-1zn8a, grandparent bf-30m2j). Aggregates the now-closed
sibling findings (bf-qvrmh test evidence, bf-59oct coverage map,
bf-4nybh gap verdicts) into one authoritative comment posted on both
umbrellas (bf-30m2j:[19], bf-1zn8a:[20]).

The close-out corrects bf-30m2j's stale premise that the disabled
acceptance_4 test is the sole coverage, and steers later children at the
genuine narrow gaps — (a) survivor-stability assertion, (b) scale-up
case, (c) golden-vector test, plus the trivial stale-comment fix —
instead of a redundant acceptance_4 rewrite.

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

notes/bf-1ccqa.md

@@ -0,0 +1,54 @@
+# bf-1ccqa — Post coverage map + gap analysis as comments (close-out)
+
+Step 4 / close-out of the Mode A partitioning coverage investigation.
+Parent umbrella: bf-1zn8a. Grandparent umbrella: bf-30m2j.
+
+## What this bead did
+
+Aggregated the now-closed sibling findings into ONE authoritative close-out
+comment and posted it on both umbrellas so the record is durable and later
+children attack the real (narrow) gaps instead of rewriting the redundant
+disabled `acceptance_4` test.
+
+- **Posted comment [19] on bf-30m2j** (grandparent) — corrects its stale premise
+  that `acceptance_4` is the only/sole coverage.
+- **Posted comment [20] on bf-1zn8a** (umbrella) — durable close-out record.
+
+(These are distinct from the parent's earlier preliminary comments [17]/[18],
+"investigative step 1", which predated the siblings closing. The close-out
+comments cite the closed siblings bf-qvrmh / bf-59oct / bf-4nybh and their
+notes files as the source of truth.)
+
+## Sources aggregated
+
+- bf-qvrmh — cargo test run evidence (notes/bf-qvrmh.md)
+- bf-59oct — per-criterion coverage map (notes/bf-59oct.md)
+- bf-4nybh — gap confirm/refute verdicts (notes/bf-4nybh.md)
+
+## Line numbers re-verified against the current working tree before posting
+
+- mode_a_coordinator.rs: `ModeACoordinator::new` :66, `rendezvous_score` :112
+  (private), separator/seed :113/115, `owns_shard` :151,
+  `set_peer_set_for_test` :306, `test_owns_exactly_one_peer_per_item` :422.
+  Module is `#[cfg(feature = "peer-discovery")]` at lib.rs:42; `default = []`
+  at Cargo.toml:66 — so these tests do NOT run in plain `cargo test`, only under
+  `--features peer-discovery` / `make test` (--all-features). Criterion 4 is
+  PARTIALLY met.
+- anti_entropy.rs: three-pods test :1541 (owner_count==1 :1623, total_owned==64
+  :1632), pod-reassignment :1665 (pod3_owned_initial :1705, re-check :1724,
+  re-homed-to-one-survivor :1734, all-64-owned :1752), partitioning-wiring
+  :1761, `with_mode_a` :199 (call sites :1581/1584/1587/1790).
+
+## Genuine gaps (the narrow holes for later children — NOT a test rewrite)
+
+- (a) No minimal-reshuffling / survivor-stability assertion in
+  test_mode_a_pod_reassignment (anti_entropy.rs:1665). CONFIRMED.
+- (b) No 3->4 scale-UP case; only 3->2 scale-down tested. CONFIRMED.
+- (c) No pinned golden-vector test locking the top1_by_score(hash(s||pid))
+  contract (rendezvous_score is private). CONFIRMED, lower priority.
+- (5) Stale comment at p13_8_anti_entropy.rs:240-244 still references removed
+  with_mode_a_scaling — trivial orthogonal edit.
+
+Directive to children: do NOT rewrite acceptance_4 (redundant). Extend
+pod-reassignment with survivor stability, add a scale-up test, add a golden
+vector, and fix the stale comment.