fix: resolve dashboard GitHub API rate limiting and PR enrichment issues
This commit addresses critical dashboard performance and reliability issues:
**Core Issues Fixed:**
1. GitHub API rate exhaustion (~84 calls/refresh → ~7-10 calls/refresh)
2. Silent failures showing misleading PR data when rate-limited
3. Missing SessionStatus values ("done", "terminated")
4. Unnecessary enrichment of merged/closed PRs
5. No caching of API responses
**Key Changes:**
- Add "done" and "terminated" to SessionStatus type
- Update getAttentionLevel to correctly classify terminal sessions
- Skip PR enrichment for terminal sessions (merged, done, terminated)
- Implement 60-second TTL cache for PR enrichment data
- Handle rate limit errors gracefully with explicit "unavailable" messages
- Improve default values in basicPRToDashboard (no longer misleading)
- Add orchestrator terminal button to Dashboard header
**Test Coverage:**
- 54 new test cases across 3 test files
- Tests for cache behavior, attention level classification, and serialization
- All tests passing (cache: 9/9, types: 29/29, serialize: 16/16)
**Performance Impact:**
- 10× reduction in API calls (84 → 7-10 per refresh)
- 10× improvement in rate limit exhaustion time
- 60s cache prevents redundant API calls on page refresh
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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