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).

tasks/docs-pg-identifier-truncation-note.md

@@ -1,7 +1,7 @@
 ---
 id: docs-pg-identifier-truncation-note
 name: Document the pg identifier-truncation collision in the release text (review 004 item 13)
-status: pending
+status: completed
 depends_on: []
 scope: single
 risk: trivial
@@ -32,12 +32,12 @@ annotation per the family's convention.
 
 ## Acceptance Criteria
 
-- [ ] `deployment.md` carries the truncation-collision note with a
+- [x] `deployment.md` carries the truncation-collision note with a
       dated annotation (mechanism + mitigation, honestly worded)
-- [ ] `engine-postgres.md` carries it too if a wake-channel section
+- [x] `engine-postgres.md` carries it too if a wake-channel section
       exists there (or the absence recorded in Notes)
-- [ ] The validation contract's no-cap verdict untouched
-- [ ] Doc gate green
+- [x] The validation contract's no-cap verdict untouched
+- [x] Doc gate green
 
 ## References
 
@@ -51,8 +51,33 @@ annotation per the family's convention.
 
 ## Notes
 
-> To be filled by implementation agent
+Deployment matrix note: `deployment.md` has no standalone wake-channel
+section — the landing site is the Postgres engine's co-tenancy
+paragraph under "Connection budgets" (the one place the matrix
+discusses naming), as a dated amendment annotation per the family
+convention. `engine-postgres.md` has no dedicated wake-channel section
+either; the note landed at the end of "Connection architecture" (the
+wake substrate lives there) with a cross-reference to the
+deployment-matrix statement. Accuracy sharpening beyond the review's
+text (verified against Postgres master `commands/async.c`):
+`pg_notify` does not merely escape identifier truncation — the server
+*rejects* channels of 64 bytes or more there ("channel name too
+long", an error), while quoted identifiers on the `LISTEN` side
+truncate to 63 bytes silently (a `NOTICE`); the notes state the
+collapse is on the registration side. The mitigation is phrased as a
+consumer obligation (names at most 63 bytes; a byte count, not a
+character count) — no validation contract change, per the task
+description.
 
 ## Summary
 
-> To be filled on completion
+Landed the pg identifier-truncation collision note in
+`docs/architecture/deployment.md` (dated annotation, Postgres engine
+section) and `docs/architecture/engine-postgres.md` (connection
+architecture, wake-substrate section) — mechanism, honest send-vs-
+registration-side statement, and the keep-names-under-63-bytes
+mitigation. Frontmatter `last_updated` of both files carried forward.
+Verified: `RUSTDOCFLAGS="-D warnings" cargo doc --no-deps` green,
+`cargo fmt --check` green, `cargo clippy --all-targets -- -D warnings`
+green; `core-contract.md`'s no-cap naming verdict untouched (diff
+touching only the two doc files).