feat: add benchmark seed provisioning (task 0025)

Add the deterministic, idempotent seed that brings a freshly provisioned
throwaway repository to a known ground truth before a trial runs, scripted
over the live Gitea API.

- bench/seed-plan.ts: the pure ground truth (fixed labels, an issue spread
  across the discriminating dimensions, and labelled/reviewed/real-branch
  pull requests) plus groundTruth(user), realizing it into a RepoState.
- bench/seed.ts: idempotent seeding reconciled by natural key, reusing
  gitea-axi's own tea-login credential discovery (no new secret handling).
- A live smoke tier (test:bench:smoke) validating the seed end-to-end and
  skipping cleanly when no host is configured, kept out of the deterministic
  bench tier.

Export selectLogin from src/context.ts so the bench reuses the exact
credential-selection path.

.claude/tasks/0025-bench-seed-provisioning.md

@@ -10,7 +10,23 @@ The seed establishes a fixed set of labels with fixed colors; a spread of open a
 
 ## Acceptance criteria
 
-- [ ] Provisioning a fresh repository and seeding it produces the fixed labels, the open/closed issue spread across the discriminating dimensions, and the pull requests (labeled, reviewed, and real-branch-backed).
-- [ ] The seed reuses gitea-axi's credential discovery rather than introducing new secret handling.
-- [ ] Re-running the seed against an already-seeded repository is idempotent — it does not duplicate or corrupt the ground truth.
-- [ ] A smoke run against the live host validates the seed end-to-end (skipping cleanly when no live host is configured, matching the existing e2e tier).
+- [x] Provisioning a fresh repository and seeding it produces the fixed labels, the open/closed issue spread across the discriminating dimensions, and the pull requests (labeled, reviewed, and real-branch-backed).
+- [x] The seed reuses gitea-axi's credential discovery rather than introducing new secret handling.
+- [x] Re-running the seed against an already-seeded repository is idempotent — it does not duplicate or corrupt the ground truth.
+- [x] A smoke run against the live host validates the seed end-to-end (skipping cleanly when no live host is configured, matching the existing e2e tier).
+
+## Implementation Notes
+
+The slice splits into two seams: `bench/seed-plan.ts` — the pure, deterministic ground truth (fixed labels, an eight-issue spread across the discriminating dimensions of the single-user-seed ADR, and three pull requests) plus `groundTruth(user)`, which realizes it into the `RepoState` the checker scores against with the shared issue/pull-request numbering a fresh repo hands out; and `bench/seed.ts` — the idempotent seeding scripted over the live Gitea API.
+The pure seam was driven test-first (`bench/seed-plan.test.ts`); the imperative seam is validated by the live smoke run (`bench/seed.smoke.test.ts`), matching the spec's testing decision that seed provisioning is validated live rather than mocked.
+
+Decisions and deviations:
+
+- **Credential reuse.** `resolveBenchAccess` reuses gitea-axi's own discovery — `listLogins` and `getToken` from `src/tea.ts` and `selectLogin` from `src/context.ts`, which was widened from private to `export` for this. No new secret handling was introduced.
+- **Smoke tier.** The live smoke test is its own vitest tier (`vitest.bench-smoke.config.ts`, `npm run test:bench:smoke`), gated on `GITEA_AXI_BENCH_LOGIN`, so the deterministic `test:bench` tier stays free of live network. Validated live against `git.alexion.dev`; the throwaway repo is deleted afterward.
+- **`readSeedSummary`.** A bounded live readback the smoke run asserts against (so it compares real state to the declared plan, not the plan to itself). It is deliberately not the full post-run state capture, which belongs to the single-cell-runner slice (task 0027).
+- **`deleteRepo`.** Added as best-effort smoke cleanup so the smoke run does not litter the live host. The spec assigns cell-loop teardown to the run loop; this is only test cleanup.
+- **Pull-request state reconciliation.** Beyond the strict re-run idempotency the smoke test exercises, `ensurePullRequest` also reopens a pull request that drifted closed (never a merged one, which Gitea cannot reopen), mirroring how `ensureIssue` reconciles issue state. This was added in response to the review to make the ground-truth declaration fully enforced.
+- **Self-review promotion.** ADR 0015 asks that whether the host permits self-approve / self-request-changes be verified during implementation. The seed only needs comment-type reviews (always permitted), and the promotion decision governs the two review *tasks*, so it is deferred to the task-suite slice (task 0028); the seed's review kinds already model all three via the `REVIEW_EVENT` map.
+
+Unaddressed review finding (see PR): the idempotency smoke test covers re-running the seed on a seed-produced repository (the literal AC-3 property) but does not separately exercise state-restoration after an external mutation, since the harness provisions a fresh repository per trial and never re-seeds an externally-mutated one.