fix(desktop-windows): wire chat quota gate into main-window send path (#10240)

[formed2forge]

Summary

Closes #10240.

The main-window send path had no pre-send quota check — it fired the request, received the server's canned "You've reached your limit" reply as a chat message, and then UsageLimitTriggerHost polled the quota endpoint post-hoc to show the upgrade popup. This is now replaced with a proper pre-send gate matching Mac's AgentBridge.quotaExceeded parity and the bar's existing FloatingBarUsageLimiter parity:

• useChat.send() calls mainChatQuotaGate.check() before the request fires. If blocked: showUsageLimit('chat') is raised immediately and the send returns — no request sent, no history entry, no canned server reply.
• UsageLimitTriggerHost now calls chatQuotaGate.sync() on the busy→idle edge to refresh the snapshot for the next send's check, instead of polling maybeTriggerChatQuotaPopup.
• maybeTriggerChatQuotaPopup removed from usageLimit.ts (no remaining callers).

Test plan

• node_modules/.bin/vitest run src/renderer/src/lib/usageLimit.test.ts src/renderer/src/lib/chatQuotaGate.test.ts src/renderer/src/hooks/useChat.test.tsx — 68/68 pass
• New describe('useChat — chat quota gate') covers: blocked send (popup shown, no fetch, no history entry) and allowed send (proceeds, recordQuery called)

Product invariants affected

• INV-CHAT-1 (one shared transcript across surfaces): this change adds a pre-send quota gate to the main-window send path, maintaining the same chat flow invariant as Mac and the bar.

Failure-Class: none

🤖 Generated with Claude Code

[Git-on-my-level]

Thanks @formed2forge — this is a clean close-out of the main-window half of #10240, and it lands exactly where the tree was waiting for it: main's UsageLimitTriggerHost.tsx still carries the TODO(#10240 stream-1 ...) asking for precisely this wiring.

What I verified on the diff:

• hooks/useChat.ts — the pre-send gate sits behind the sendingRef re-entrancy latch and ahead of setBusy(true), so a blocked send leaves no history entry and doesn't trip the busy state. Signed-out users fail open, and recordQuery() keeps the optimistic delta honest between syncs (the same contract the bar's barSend.ts already uses).
• components/settings/billing/UsageLimitTriggerHost.tsx — the busy→idle edge now calls mainChatQuotaGate.sync() instead of the post-hoc quota probe; the 60s sync floor in chatQuotaGate.ts keeps that from becoming a per-reply network hit, and the exported singleton is the right shape for it.
• lib/usageLimit.ts + lib/usageLimit.test.ts — maybeTriggerChatQuotaPopup is fully removed along with its tests. Two prose mentions survive elsewhere (a historical comment in chatQuotaGate.ts and docs/mac-parity-audit/track2-groundtruth/07-usage-limiter.md); a small follow-up touch-up would be nice but nothing blocks on it.
• hooks/useChat.test.tsx — the two new cases cover the behavioral difference that matters: blocked send shows the popup with no fetch and no history entry; allowed send proceeds and records the query optimistically.
• changelog/unreleased/2026-08-chat-quota-gate.json — accurate one-line user-facing description of the change.

The blocker is branch state, not the change: the branch carries 43 upstream commits after its last sync, which is why GitHub shows a 208-file diff and conflicts against main. Everything outside the six files above is content that already landed through merged PRs (#11933, #12019, #12089, #12096, #12109, …), including all of the workflow/AGENTS.md/monitoring churn in the file list. Syncing your fork with upstream and rebasing fix/windows-chat-quota-gate onto current main will collapse the PR to just your six files and let Actions run the vitest suites — your reported 68/68 across usageLimit / chatQuotaGate / useChat matches the exact test count at this head, so CI should confirm quickly.

Leaving for human maintainer review before merge: routine sign-off on the rebased head once CI confirms the three suites — the Mac-parity direction itself is already settled in the issue and in chatQuotaGate.ts, so no product decision is needed.

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by AI on behalf of David.

[formed2forge]

Rebased onto current main — PR now shows 6 files (the 6 Windows files in the fix commit). Mergeable.

[Git-on-my-level]

Thanks @formed2forge — the rebase did exactly what was asked: the PR now shows just the six Windows files from the fix commit, and GitHub reports it mergeable with no conflicts.

I re-verified on the rebased head (beac65a):

• Ran the three affected suites at this commit in a clean worktree: 68/68 pass (usageLimit 8, chatQuotaGate 25, useChat 35) — matches your test plan exactly.
• hooks/useChat.ts — gate still sits behind the re-entrancy latch and ahead of setBusy(true); blocked sends show the popup with no request and no history entry, and the signed-out fail-open guard mirrors the bar's isSignedIn() pattern in barSend.ts.
• components/settings/billing/UsageLimitTriggerHost.tsx — busy→idle edge now refreshes the gate snapshot; the 60s sync floor in chatQuotaGate.ts keeps that off the per-reply network path.
• lib/usageLimit.ts / usageLimit.test.ts — maybeTriggerChatQuotaPopup fully removed, no dangling importers.
• changelog/unreleased/2026-08-chat-quota-gate.json — accurate and matches the fragment convention.

One cosmetic nit, no action needed: the new in-quota test uses void act(...) without awaiting, which trips a React act() warning on stderr.

CI has re-queued on the new head — Desktop Checks is green; Desktop Windows CI was still pending at review time. Removed the stale needs-rebase label. Leaving merge sign-off to a human maintainer.

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by AI on behalf of David.

[formed2forge]

Rebased and all 68/68 tests pass. Ready for maintainer merge sign-off.

[formed2forge]

The Detect Changes job is failing due to runner starvation — a pure CI infrastructure issue unrelated to this PR. Could a maintainer re-run? Once green this is ready for review.

[kodjima33]

Clean, scoped desktop bug fix (chat quota pre-send gate, closes #10240), matches Mac/bar parity pattern, tests added, not already fixed on main. Stale Android/Dart 'Detect Changes' check re-ran clean. Owner-override (desktop fix).