feat: Track PR outcomes end-to-end in task history

[whitmo]

Summary

• Add --pr-url flag to agent complete so workers can report which PR they created when signaling completion
• Record PR URL/number in task history during worker cleanup (previously PRURL and PRNumber fields were always empty)
• Add PR outcome tracking daemon loop (every 5 min) that polls GitHub for open/unknown task history entries and updates their stored status to merged/closed/open via the previously-unused UpdateTaskHistoryStatus method
• Use stored terminal statuses (merged/closed/failed) in CLI display to avoid redundant GitHub API calls
• Add GetPendingTaskHistory state method to efficiently query entries needing outcome checks
• Add parsePRNumber and ghStateToTaskStatus helpers with comprehensive tests
• Update Socket API and State File extension documentation

What was broken before

The task history system had the infrastructure but wasn't wiring it together:

• UpdateTaskHistoryStatus() and UpdateTaskHistorySummary() existed but were never called in production (dead code)
• PR URL/number were never captured - fields were always empty
• Status was always "unknown" (unless failure) - outcomes were only queried at display time via GitHub API with no persistent record

Data flow (after)

Worker creates PR → agent complete --pr-url <url> → handleCompleteAgent stores PRURL on agent → recordTaskHistory extracts PR number, sets status=open → PR outcome loop (5 min) polls GitHub for open/unknown entries → UpdateTaskHistoryStatus persists merged/closed/open → repo history uses stored status for terminal states 

Test plan

• TestGetPendingTaskHistory - returns only open/unknown entries with branches
• TestGetPendingTaskHistoryNonExistentRepo - error handling
• TestRecordTaskHistoryWithPRURL - PR URL/number captured, status set to open
• TestRecordTaskHistoryWithPRURLAndFailure - failure status takes precedence over PR
• TestParsePRNumber - URL parsing edge cases
• TestGhStateToTaskStatus - GitHub state mapping
• All existing tests pass (go test ./...)
• verify-docs state schema check passes

🤖 Generated with Claude Code

[whitmo]

Triage Review

Priority: P1 (Task history - roadmap item)
Build: Pass
Tests: Pass (all internal packages)
Merge conflicts: None - merges cleanly with main and all other open PRs
Roadmap alignment: Directly addresses P1 "Task history" item

Changes:

• Adds pr_url field to Agent state and complete_agent socket API
• Live PR status queries via gh pr view in history display
• Supports merged/closed/open status tracking
• Updates Socket API and State File extension docs

Recommendation: Safe to merge anytime - no conflicts with any other PR.

[whitmo]

Local CI Verification (2026-03-12)

Check	Result
go build	PASS
go vet	PASS
go test ./...	PASS (all packages)

CI Status: No GitHub Actions checks are running — this is expected for first-time fork PRs. GitHub requires a maintainer to approve workflow runs for PRs from forks.

Branch is rebased on upstream/main (0 commits behind). Ready for maintainer review and CI approval.