Tier GitHub PR lookup polling to prevent quota exhaustion (#12013)

* Tier GitHub PR lookup polling to prevent quota exhaustion

The selected worktree (O(1)) checks per-minute; card list (O(N)) per-15-minutes.
Introduce process-wide cache to collapse concurrent polling and gate lookups on
available rate-limit budget with exponential backoff on failure.

- Preserve last-known review during backoff
- Invalidate cache when Orca opens a PR
- Stop coordinator from double-charging

* Tier GitHub PR lookup polling to prevent quota exhaustion

- Return the latest reset time when both GitHub API buckets are rate-limited, preventing premature retries against still-blocked buckets.
- Serve the last known review on transient lookup failures, preventing reviews from blinking out on temporary errors.
- Discard in-flight lookups that predate an invalidation so stale answers cannot overwrite newly opened reviews.

* fix: give rate-limit reset tests unique titles

oxlint vitest/no-identical-title was failing static analysis because two
cases shared the same describe title.

src/main/github/client.test.ts

@@ -170,6 +170,7 @@ import {
   getPRComments,
   getPRForBranch,
   getPRForBranchOutcome,
+  getGitHubPRLookupRateLimitBlock,
   getRepoSlug,
   getRepoUpstream,
   getWorkItem,
@@ -4609,3 +4610,70 @@ describe('GitHub GraphQL rate-limit guard', () => {
     expect(noteRateLimitSpendMock).not.toHaveBeenCalled()
   })
 })
+
+describe('getGitHubPRLookupRateLimitBlock', () => {
+  beforeEach(() => {
+    execFileAsyncMock.mockReset()
+    ghExecFileAsyncMock.mockReset()
+    getOwnerRepoMock.mockReset()
+    getOwnerRepoMock.mockResolvedValue({ owner: 'acme', repo: 'widgets' })
+    getRemoteUrlForRepoMock.mockReset()
+    gitExecFileAsyncMock.mockReset()
+    getRateLimitMock.mockReset()
+    getRateLimitMock.mockResolvedValue(undefined)
+    rateLimitGuardMock.mockReset()
+    rateLimitGuardMock.mockReturnValue({ blocked: false })
+    noteRateLimitSpendMock.mockReset()
+    _resetOwnerRepoCache()
+  })
+
+  it('reports no block while every lookup bucket has budget', async () => {
+    await expect(getGitHubPRLookupRateLimitBlock('/repo-root')).resolves.toBeNull()
+    expect(getRateLimitMock).toHaveBeenCalled()
+  })
+
+  it('reports a block when either lookup bucket is exhausted', async () => {
+    rateLimitGuardMock.mockImplementation(((bucket: string) =>
+      bucket === 'graphql'
+        ? { blocked: true, remaining: 4, limit: 5000, resetAt: 1_800_000_000 }
+        : { blocked: false }) as () => RateLimitGuardResult)
+
+    await expect(getGitHubPRLookupRateLimitBlock('/repo-root')).resolves.toEqual({
+      resetAt: 1_800_000_000
+    })
+  })
+
+  it('reports the latest reset when both lookup buckets are exhausted', async () => {
+    rateLimitGuardMock.mockImplementation(((bucket: string) => ({
+      blocked: true,
+      remaining: 4,
+      limit: 5000,
+      // Why: core resets first, so returning it would retry into graphql's block.
+      resetAt: bucket === 'core' ? 1_800_000_000 : 1_800_003_600
+    })) as () => RateLimitGuardResult)
+
+    await expect(getGitHubPRLookupRateLimitBlock('/repo-root')).resolves.toEqual({
+      resetAt: 1_800_003_600
+    })
+  })
+
+  it('reports the later reset when graphql outlasts core', async () => {
+    // Retrying at the earlier reset would fail again on the bucket still blocked.
+    rateLimitGuardMock.mockImplementation(((bucket: string) => ({
+      blocked: true,
+      remaining: 0,
+      limit: 5000,
+      resetAt: bucket === 'graphql' ? 1_800_000_600 : 1_800_000_000
+    })) as () => RateLimitGuardResult)
+
+    await expect(getGitHubPRLookupRateLimitBlock('/repo-root')).resolves.toEqual({
+      resetAt: 1_800_000_600
+    })
+  })
+
+  it('fails open when the exempt rate-limit probe itself fails', async () => {
+    getRateLimitMock.mockRejectedValue(new Error('probe offline'))
+
+    await expect(getGitHubPRLookupRateLimitBlock('/repo-root')).resolves.toBeNull()
+  })
+})