Plugin System Phase 3: Tracker Slot (#9)

[tu11aa]

Summary

Phase 3 of issue #9 (Plugin/Extension System). Abstracts GitHub issue/PR operations behind a `TrackerDriver` interface mirroring phase 1 runtime (PR #20) and phase 2 workspace (PR #26). GitHub is the sole provider; Linear/Jira/GitLab are explicit follow-ups. Per design, polling stays provider-specific (`poll-github.sh` unchanged); only one-shot ops go through the driver.

Spec: `docs/specs/2026-04-21-plugin-system-tracker-design.md`
Plan: `docs/specs/2026-04-21-plugin-system-tracker-plan.md`

What changed

New:

• `src/trackers/types.ts` — `TrackerDriver`, `Issue`, `PullRequest`, `CheckRun`, `ReviewDecision`, `TrackerScope`, `TrackerProbeResult`, `IssueFilter`, `TrackerFactory`
• `src/trackers/github.ts` — `createGitHubDriver(scope)` — 8 methods via gh CLI
• `src/trackers/registry.ts` — `TrackerRegistry` with `forProject`, `get`, `probeAll`
• `src/trackers/index.ts` + tests: 15 github, 7 registry, 3 memory-tracker = 25 new tests
• `src/trackers/tests/helpers/memory-tracker.ts` — in-memory fixture
• `src/commands/tracker.ts` — `cockpit tracker create-issue|merge-pr|get-checks|get-run-log|list-issues` CLI

Migrated:

• `scripts/execute-reaction.sh` — `auto-merge` case now calls `cockpit tracker merge-pr`; `auto-fix-ci` uses `cockpit tracker get-checks --json` + `cockpit tracker get-run-log`. Zero `gh` refs remain in the script.
• `src/commands/doctor.ts` — probes tracker providers via `probeAll()`; adds `Tracker 'github' installed` + `authenticated` checks.

Config (backward compatible):

• `tracker?: string` at top level and per-project. Absent = `"github"`.

Docs:

• README — commands table + config JSON + Tracker Abstraction architecture subsection.

Contract highlights

• Primitive ops only. No N+1 enrichment in the driver (reviewer-validated decision). Callers that need enrichment compose `listPullRequests` + `getPullRequestChecks` themselves.
• Async throughout. Matches runtime (phase 1) and workspace (phase 2) patterns.
• Provider-specific polling stays. `poll-github.sh` unchanged — future Linear adds `poll-linear.sh` alongside. Hybrid decision documented in spec.

Intentionally NOT migrated (per spec §Non-Goals)

• `scripts/poll-github.sh` — canonical GitHub polling
• `scripts/match-reactions.sh` — provider-agnostic already
• `src/commands/feedback.ts` — opens a browser URL (no `gh issue create` today). Spec incorrectly listed it; plan corrected.
• GitHub Project-board GraphQL — already a TODO; stays for now.
• Cross-tracker vocabulary normalization in `reactions.json` — follow-up #27.

Test plan

• `npm run test -- --run`: 107 pass, 2 pre-existing `config.test.ts` failures (emoji-prefix baseline, predates this PR)
• `npm run lint` exits 0
• `npm run build` exits 0
• `grep -cE "gh (pr|run|api|issue)" scripts/execute-reaction.sh` = 0
• `cockpit doctor` shows new `Tracker 'github'` lines
• `cockpit tracker --help` shows 5 subcommands
• Manual smoke: reactor auto-merge on a test PR (tested by reviewer)
• Manual smoke: reactor auto-fix-ci dispatch

Pre-PR code review

Internal review (superpowers:code-reviewer) approved with 2 Important items, both addressed in commit `7f3c069`:

• merge-pr `--method` validation — was silently normalizing invalid values to squash; now errors with `Invalid merge method 'foo'. Allowed: merge, squash, rebase`.
• Missing-repo error message — opaque `scope.owner required` replaced with actionable `No tracker repo configured for project 'X' (set reactions.json github.repos.X.owner/repo)`.

Other findings (shell-injection surface on `escape()`, runId regex fragility, probeAll bogus scope) tracked for phase-4+ polish; noted in PR comments.

Follow-ups already filed

• #27 — Normalize cross-tracker vocabulary in `reactions.json` once a 2nd tracker ships