fix(tests): drain three base-reds left by the SSE-comment default and a locale gap

[diegosouzapw]

Three reds that reproduce on a pristine checkout of the release tip, with zero local changes.
None is caused by the branch that surfaced them (a docs/Dockerfile PR, #10701, whose full unit
run exposed them).

1. i18n-vi-completeness — 3 tests

Six keys landed in en.json with no Vietnamese counterpart:
settings.reasoningTokenBuffer(Desc), settings.zeroLatencyOptimizations(Desc),
settings.compressionOutputStyle.i-have-adhd.{label,description}. The vi locale is held to
strict parity, so the whole suite went red.

Translated. No existing key reordered — the diff is 9 added lines.

2. chatcore-translation-paths — "emits final SSE metadata comments before [DONE]"

#10539 flipped OMNIROUTE_SSE_COMMENTS to off-by-default (strict SSE clients JSON.parse every
line and crash on : comments) and updated three sibling tests — but not this one, which
asserted the trailer is emitted.

The test now asserts the current contract: the stream is comment-free, still ends with [DONE],
and the metadata still reaches the client through the X-OmniRoute-* headers. The opt-in half —
trailer present, after the finish chunk, before [DONE] — stays covered by
sse-comments-optout-9305.test.ts, which drives the env var through all three states.

First attempt was to set OMNIROUTE_SSE_COMMENTS=on inside the test. That turned one red into
a different one: the env var leaks into the sibling call-log tests in the same file (chatCore records Claude prompt cache… started failing, and passes in isolation). Reverted.

3. chat-messages-validation-6402 — all 9 Antigravity cases

These asserted assert.match(body, /ok/) against the mocked model output. That text never
reached this layer. The match only ever succeeded on the ok inside
: x-omniroute-tokens-in=0 — an SSE comment trailer. Dumping the body at the last passing
commit shows it contained only trailers, no model text:

": x-omniroute-cache-hit=false\n: x-omniroute-latency-ms=26\n…: x-omniroute-tokens-in=0\n…"

When the trailers stopped being emitted, the coincidence broke — not the behavior. Bisected to
6b823aa441 (its parent 6d99a46d4b passes); forcing OMNIROUTE_SSE_COMMENTS=on at the tip
reproduces the trailers-only body, confirming nothing about content relay changed.

The test now asserts the guard it is named for: a cloudcode envelope (no messages key) must
not be rejected by the #6402 missing-messages validator. Real content-relay coverage for this
provider lives in antigravity-streaming-passthrough.test.ts (passes, asserts
choices[0].message.content === "Hello again").

Verification

Suite	Before	After
i18n-vi-completeness	2 pass / 3 fail	5 pass / 0 fail
chatcore-translation-paths	69 / 1	70 / 0
chat-messages-validation-6402	5 / 9	14 / 0

Base-reds still open (not in this PR)

Seven more files reproduce on the same tip and need their own triage — some may be product
regressions rather than stale tests:

antigravity-model-aliases (3) · glm-provider-model-import-route (7) · executor-qwen-web (1) ·
hard-session-lease-bypass-inventory (1) · i18n-glossary-consistency-check (1, zh-TW) ·
instrumentation-warm-catalog-cache (2) · model-sync-route (2)

Plus npm run lint: 25 errors in tests/unit/cli-oauth-commands.test.ts and
tests/unit/executor-gitlab.test.ts.

Inventory posted to #9985. Note that Release-Green reported "Validate active release branch:
success" while all of these were red, so that signal is not covering the unit suite the PR
checks run.

Refs #9985, #10539