docs: the pg LISTEN identifier-truncation wake-collision note (review 004 item 13)

deployment.md's Postgres co-tenancy paragraph and engine-postgres.md's
connection-architecture wake-substrate section now carry the 63-byte
identifier-truncation collision note as dated annotations: two names
longer than 63 bytes sharing a 63-byte prefix silently register the
same server-side wake channel; pg_notify (the parameter path, untrun-
cated, rejecting >= 64-byte channels) is unaffected, so the collapse is
on the registration side. Mitigation: keep mechanism names at most 63
bytes (byte count). The naming contract's deliberate no-cap verdict is
untouched. Discharges review 004 'findings recorded, not fixed' item
13 (task docs-pg-identifier-truncation-note).

docs/architecture/deployment.md

@@ -1,6 +1,9 @@
 ---
 status: stable
-last_updated: "2026-10-11 (the log-facade decision of record landed —
+last_updated: "2026-10-11 (the pg identifier-truncation wake-collision
+note — review 004 item 13's doc-fix disposition — added to the
+Postgres engine section).
+Earlier the same day: the log-facade decision of record landed —
 [ADR-025](decisions/025-log-facade.md): engine diagnostics route
 through the `tracing` facade, silent by default, subscriber wiring on
 the consumer/binary; the diagnostics-posture section added below.
@@ -90,6 +93,28 @@ engine-owned PostgreSQL schema (default `alkstore`, per-engine option)
 — layout per [ADR-010](decisions/010-queue-semantics-depth.md) §8
 (resolved from [queues.md](queues.md)'s namespace bullet).
 
+One pg-specific naming caveat, dated per the family's amendment
+convention *(annotated 2026-10-11 — review 004 item 13, recorded
+"not fixed" in the review with a fold-into-the-next-doc-pass
+disposition; this note is that fix)*: the wake machinery
+interpolates the channel as a quoted SQL identifier on
+`LISTEN`/`UNLISTEN`, and PostgreSQL truncates identifiers to
+**63 bytes (`NAMEDATALEN` − 1)** server-side — with only a
+`NOTICE`, never an error — so two distinct names longer than 63
+bytes sharing a 63-byte prefix register the **same** server-side
+wake channel (a silent cross-channel collision). The `pg_notify`
+path is unaffected by the truncation — it carries the channel as a
+text parameter, not an identifier, and the server rejects channels
+of 64 bytes or more there ("channel name too long") — so the
+collapse is on the registration side. The
+[naming contract](core-contract.md#naming--reserved-namespace)
+deliberately caps no name (the length-independence verdict stands),
+so nothing engine-side warns. Mitigation:
+**keep mechanism names under the PostgreSQL identifier limit —
+at most 63 bytes; the limit counts bytes, not characters, so
+multibyte names reach it sooner.** Distinct names within the limit
+cannot collide.
+
 ### Mem engine
 
 - No connections — there is nothing to budget. The engine instance