fix: add retry, timeout, and rate-limit handling to GitHub API scripts

[WYSIATI]

Summary

• Extract a shared githubRequest utility (scripts/github-request.ts) that wraps fetch() with retry, timeout, and rate-limit handling
• Migrate all 4 GitHub API scripts to use the shared utility, eliminating 4 copies of inline githubRequest functions
• Add 52 unit and integration tests (scripts/github-request.test.ts)
• Previously, a single ECONNRESET or GitHub 502 would crash these CI scripts with no recovery

What's included

The shared utility adds:

• Exponential backoff retry (default 3 attempts) for transient network errors (ECONNRESET, ECONNREFUSED, EPIPE, ETIMEDOUT, EAI_AGAIN, etc.)
• Retry on retryable HTTP status codes (408, 429, 500, 502, 503, 504)
• Respect for Retry-After headers from GitHub's rate limiter
• Per-request timeout (30s default) via AbortController
• 204 No Content handling — returns {} instead of crashing on .json() parse
• Jitter (±25%) to avoid thundering herd on concurrent retries

Test architecture

Tests use Bun's native test runner (bun:test) and are structured as:

Unit tests (internal helpers exported for testability):

• isTransientError — parameterized via test.each() across all 10 transient error codes + Bun socket message + AbortError/TimeoutError + negative cases
• calculateDelay — exponential backoff curve, jitter range, cap at 32s
• parseRetryAfter — numeric seconds, HTTP-date, edge cases (0, negative, >300s cap, missing header)

Integration tests (end-to-end githubRequest):

• Basic requests: GET with auth, POST with JSON body, 204 No Content, custom/default User-Agent
• Non-retryable errors: test.each([401, 403, 422]) — immediate throw, 1 attempt
• Transient network error retry: test.each(["ECONNRESET", "EPIPE", "ETIMEDOUT", "ECONNREFUSED"]) — recovers after N failures
• Retryable HTTP codes: test.each([429, 500, 502, 503, 504]) — retries and recovers
• Retry exhaustion — correct attempt count, throws final error
• maxRetries=0 — disables retry for both network and HTTP errors
• Mixed scenarios — ECONNRESET → 502 → success in one request
• Timeout — AbortController fires, AbortError retried

$ bun test scripts/github-request.test.ts
52 pass, 0 fail, 84 expect() calls

Scripts updated

Script	What it does	Why retry matters
auto-close-duplicates.ts	Closes duplicate issues after 3-day grace period	Makes hundreds of sequential API calls; a single 502 would abort the entire batch
backfill-duplicate-comments.ts	Triggers dedupe workflows on issues missing duplicate detection	Paginates through up to 200 pages of issues; transient failures are inevitable
lifecycle-comment.ts	Posts lifecycle label comments on issues	Single POST — retry prevents silent failure in CI
sweep.ts	Marks stale issues and closes expired ones	Most API-intensive script; pagination + per-issue events/comments queries

Test plan

• bun test scripts/github-request.test.ts — 52/52 passing
• Run bun run scripts/sweep.ts --dry-run — verify no behavioral change in normal path
• Verify retry logging: mock a 429 or 502 response to confirm [RETRY] messages appear with backoff delays
• Verify non-retryable errors still throw immediately (e.g., 401, 403, 422)