fix(sse): shrink chat.ts back under the frozen file-size cap (base-red drain)

[diegosouzapw]

Summary

npm run check:file-size (job ci.yml:lint) was red on the release/v3.8.50 tip:

[file-size] 1 violação(ões):
  ✗ src/sse/handlers/chat.ts: 1880 > congelado 1877 (não pode crescer)

Every PR cut against that tip inherited the failure, so this drains it at the source.

Cause

The exact-model lock scope merged with #8630 expanded an inline argument object at the
recordModelLockoutFailure() chokepoint from 1 line to 4:

{
  maxCooldownMs: mlSettings.maxCooldownMs,
  scope: provider === "antigravity" ? "exact" : undefined,
}

Net +3 on a frozen god-file that had no headroom.

Fix — shrink, not rebaseline

Hoisted the ternary into a lockScope const so the object collapses back to one line, and
condensed the adjacent comment (the #8630 rationale is preserved in it). Behaviour is
identical — same ternary, same argument value.

src/sse/handlers/chat.ts: 1880 → 1877, exactly at the frozen cap. No baseline entry was
added — config/quality/file-size-baseline.json is untouched.

Out-of-scope line in the diff (disclosed)

The diff also contains one Prettier normalisation at line 1547 (an isTerminalStreamEarlyEof
condition from #9184). That line was already failing prettier --check on the base tip —
verified with git show origin/release/v3.8.50:src/sse/handlers/chat.ts | npx prettier --check.
It is behaviour-neutral and leaves the file Prettier-clean.

Validation

Check	Result
npm run check:file-size	OK — 124 arquivos congelados + OK — 44 test files congelados
npm run typecheck:core	exit 0
npx eslint src/sse/handlers/chat.ts (with suppressions)	exit 0, clean
npx prettier --check src/sse/handlers/chat.ts	All matched files use Prettier code style!
model-lockout + account-fallback suites	93/93 pass (model-lockout-decay, model-lockout-max-cooldown, model-lockout-exact-cooldown-cap, repro-antigravity-404-family-cooldown-hijack, account-fallback-service)

The exact-model behaviour #8630 introduced stays covered — Antigravity 404 Model Not Found locks exact model ONLY, not entire family and Antigravity 429 Rate Limit locks whole family
both pass.

No production behaviour changes, so no new test is added; the existing 93 assertions are the
regression guard for the wiring this touches.

Refs #8630