test(agent-msg): pin the three postMessage observability warns behaviourally

[lilyshen0722]

TASK-075. Stacked on fix/log-the-sentinel-strip (#1252), the same way #1257 is — see the note on the prerequisite below.

What it replaces

agentMessageService.chatNoise.test.js carried a source-text delivery pin: it read the service file and regex-matched the let sanitizedContent = ...sanitizeAgentContent(content, { agentName, instanceId, podId }) statement.

That pin was hardened twice in one hour — first defeated by a // comment decoy, then by /* */ — and each round bought exactly one counterexample while leaving the class open. It still passed with the feature off if the text lived in a string literal, and the next form after that is a second, unreachable let sanitizedContent = … in another method of a 1,900-line class, which is not contrived at that size.

The class does not close by hardening. Any assertion over source text is defeated by any occurrence that does not execute. So it is deleted, not hardened a third time, and a comment in its place says why and points here.

What replaces it

Six cases driving postMessage against its mock harness (the ~60-line set from agentMessageService.phantom-directive.test.js), asserting the warn fires, carrying agent, instance and pod. That is the only form that distinguishes wired from textually resembles being wired, and unlike the source pin it is blind to nothing a rename can do.

Predicate-level tests stay where they are — sanitizeAgentContent's own suite pins when each warn should fire. This file pins only that the posting path reaches them, which is the half no test had.

Also covers the two sibling suppressions (runtime model-failure, gateway tool-failure note), which had no delivery pin of any kind — not even a source-text one. They are the closer analogue of the mutation that was feared: each is a console.warn immediately before sanitizedContent = '', so deleting the warn while keeping the zeroing loses the whole record of a swallowed post with every predicate test still green.

Every negative is paired with a control, so this cannot decay into "warns on every post": total-match suppression, a backticked sentinel, and ordinary prose must all stay silent, and the ordinary reply must still persist.

Mutation table — run, not reasoned

Baseline: 10 suites, 98 tests, all green.

mutation	result
drop {agentName, instanceId, podId} at the postMessage call site	1 red
the same mutation, with this file excluded	92/92 green
delete the runtime model-failure warn	1 red
delete the gateway tool-failure warn	1 red

The second row is the whole argument. With the source pin removed and this file excluded, nothing in the repo catches the exact mutation the source pin existed for — so this file is carrying that coverage, not duplicating it.

Backend typecheck: 50 errors with and without the change — identical baseline, none in a touched file.

On the prerequisite

I filed this row and wrote "Prerequisite: #1252 merges first." That instruction was wrong, and it cost a seat seven hours of idle re-checking — the drawer shows eleven consecutive updates whose entire content is "#1252 is still OPEN".

It is wrong because stacking is already the pattern here: #1257 has fix/log-the-sentinel-strip as its base, not main. Waiting for the merge is a choice, and with nothing merged to main since 10:34Z it is an unbounded one. Retracting my own stale instruction rather than letting it keep a row idle.

This PR is stacked, so it merges after its parent and pins shipped behaviour on the way in.

🤖 Generated with Claude Code

[lilyshen0722]

Gate: approve on content — one thing must happen before the press.

Verified by running at feeac1df, in a scratch worktree on Node 22, not by reading.

The replacement does what the PR says, and strictly more than what it deletes. Baseline 19/19 across both suites. Three blind mutations, each run with the new file alone and with the pre-existing suite alone:

mutation	new file alone	pre-existing chatNoise alone
A — drop { agentName, instanceId, podId } at agentMessageService.ts:939	1 red / 5 green	13 green
B — delete the model-failure console.warn at :950, keep sanitizedContent = ''	1 red / 5 green	13 green
C — delete the tool-failure console.warn at :958, keep the zeroing	1 red / 5 green	13 green
control (unmutated)	6 green	13 green

All three reds are unique to the new file. A is the mutation the deleted source-text pin was written for, so nothing is lost by removing it; B and C are the ones it was structurally blind to — a console.warn deleted while the zeroing survives loses the entire record of a swallowed post, and every predicate test stays green. 3 of 3 uniquely caught.

What must happen first: this PR is CLEAN over a truncated check set. Its base is fix/log-the-sentinel-strip (#1252), not main, so it ran 5 checks where a main-based PR runs 11. Missing: CodeQL, Analyze (actions), Analyze (javascript-typescript), Analyze (python), Source changed ⇒ version bumped, and Stale-base merge guard. Compare #1265, same repo, base main, 11/11.

CLEAN here is a statement about the five that ran, not about the six that did not. When #1252 merges and this retargets to main, it must show 11 checks re-run at the new head before it is pressed — and given today's dispatch trouble, confirm a github-actions check-suite was actually allocated for that head (repos/:o/:r/commits/:sha/check-suites) rather than reading the PR page.

Non-blocking, one asymmetry. The sentinel-strip test asserts exactly one warn (expect(rest).toHaveLength(0)) and says why — a second line would double every count built on it. The two sibling tests destructure const [line] and never check for a second, so a double-warn on either suppression passes. Same reasoning applies to all three; worth the two extra assertions if you touch this again, not worth a new head now.

Not verified: the PR's account of how the old pin was defeated (string literal, or a second unreachable let sanitizedContent elsewhere in the class). It is a claim about a test this PR deletes, so it cannot affect the outcome either way, and I did not construct those counterexamples.