docs(changelog): Unreleased section for the smoke node assertion + agent-browser correction

Summarises what changed since v1.8.13: the node-major assertion (a bump would
have passed the suite silently), the two-sided verification of the derivation,
and the v1.8.13 agent-browser 0.35.2 -> 0.36.0 correction. No image content
changes; NODE_VERSION still 22.

CHANGELOG.md

@@ -11,6 +11,53 @@ Pre-v1.0.0 tags followed the pi npm version (`v{pi_version}[letter]`).
 
 ---
 
+## Unreleased
+
+**A test that was quietly checking nothing, and a version number that was wrong.**
+Both found by delegating a read-only audit of this repo to a headless worker
+(`pi-toolkit` `bin/pi-task`) and then spot-checking its pointers from the
+filesystem — 5 of 5 held, and it also corrected a false premise planted in its
+own brief.
+
+**The node major is now asserted, not merely printed.**
+`scripts/smoke-test.sh` ran `run "node" "node --version"`, which asserts only
+that the binary exists and exits 0 — the printed version was compared to
+nothing. The line above it has always used `run_expect` against
+`$EXPECTED_PI_VERSION` for `pi`, so the suite *looked* like it covered node.
+**A node major bump would have passed the whole smoke suite silently.** Worse,
+this is where the "node v22.23.2 verified" line in the v1.8.13 recreate notes
+came from: printed output, not an assertion — an expectation stated up front and
+then falsified by the check.
+
+Now gated on `EXPECTED_NODE_MAJOR`, which CI derives from `Dockerfile.base`'s
+`ARG NODE_VERSION` — the single source of truth, and the *only* hard node pin in
+the repo (`Dockerfile.variant` has no node install at all, so the two Dockerfiles
+cannot disagree). That also catches a stale cached layer whose node disagrees
+with the declared ARG. Unset ⇒ previous behaviour, so nothing breaks for anyone
+running the suite by hand.
+
+Verified two-sided, because a silent failure here reintroduces the exact bug it
+fixes: the `sed` derivation yields `22` (an empty result would disable the
+assertion silently); `grep -Fq "v22."` matches `v22.23.2`; `"v24."` does **not**
+match, so a wrong major is caught; `"v2."` does not prefix-collide. The workflow
+YAML was re-parsed after editing (9 jobs).
+
+**v1.8.13's agent-browser version was wrong.** That entry said "the image's own
+0.35.2". The image ships **0.36.0** — `/usr/lib/node_modules/agent-browser` at
+0.36.0 with `engines.node >=24.0.0`, and no 0.35.2 exists anywhere in the image.
+The sentence was also internally incoherent, contrasting 0.36.0 against a version
+that is not present. Corrected in place with a visible note, since that entry is
+already released. **The reasoning survives untouched**: the engines floor really
+is vestigial, because `/usr/bin/agent-browser` is a prebuilt aarch64 ELF invoked
+directly and never through node — which is exactly why 0.36.0 runs fine on
+22.23.2, consistent with the runtime proof collected on 2026-09-07 and with the
+retraction of the earlier false "0.36.0 requires node >= 24" alert.
+
+No image content changes: `NODE_VERSION` still 22, no pins moved. This is a test
+and a docs correction only.
+
+---
+
 ## v1.8.13 — 2026-09-06
 
 **Version audit + three pins moved, one deliberately not moved.** `pi`