[ci-doctor] CI Test Failure — Run #25838576963 (merge of autoloop PR #302)

The `Test & Lint` job failed at the `Test` step after merging PR #302. All 7216 tests pass locally with bun 1.3.14.

## Failure Details
- **Run**: [25838576963](https://github.com/githubnext/tsessebe/actions/runs/25838576963)
- **Commit**: `3bf6010ebfc9b366e76d46b2fb836eebc2c1bb5a`
- **Trigger**: push (merge of autoloop PR #302: extensions, pdArray, format_table)
- **Failed Step**: `bun test --coverage ./tests/`

## Root Cause Analysis

The exact test failure output is unavailable (CI logs require admin access). Investigation found:

1. **All tests pass locally** — `bun test --coverage ./tests/` passes with 7216 tests, 0 failures
2. **Type check passes** — `tsc --noEmit` succeeds
3. **Lint passes** — 618 warnings, 0 errors

**Primary suspect**: The CI uses `bun-version: latest` (via `oven-sh/setup-bun@v2`), which may have installed a **newer bun version** with a regression in the test runner or coverage behavior.

## Historical Pattern

This is a **recurring failure** — an identical `Test & Lint` failure at the `Test` step occurred on run [25717961425](https://github.com/githubnext/tsessebe/actions/runs/25717961425) on 2026-05-12 when merging autoloop PR #297. Both failures follow the same pattern: autoloop merges to main → `bun test` step fails → tests pass locally.

## Changes in PR #302

New files: `src/core/extensions.ts`, `src/core/pd_array.ts`, `src/stats/format_table.ts`, corresponding test files, and playground pages.

Notable: `tests/playground.test.ts` correctly added `extensions.html` to `NON_PLAYGROUND_PAGES` since it is a static reference page (no interactive playground blocks).

## Recommended Actions

- [ ] **Pin bun version** in `.github/workflows/ci.yml`: change `bun-version: latest` to `bun-version: "1.3.14"` to avoid upstream regressions
- [ ] **Retry the failed run** — if flaky, a re-run may succeed
- [ ] **Inspect actual CI logs** (requires admin) to find the exact failing test

## Prevention Strategies

1. Pin bun to a specific version in CI; update deliberately and review release notes
2. Add GitHub Actions retry for flaky tests

## AI Team Self-Improvement

```
## CI Stability Notes
- Never use `bun-version: latest` in CI workflows — always pin to a specific version.
- When adding new playground pages that are static (no interactive code), add them to
NON_PLAYGROUND_PAGES in tests/playground.test.ts.
- New test files using module-level global state (registries, caches) must ensure tests
are order-independent and do not rely on side effects from other test files.
```

> [!WARNING]
>
> Firewall blocked 1 domain
>
> The following domain was blocked by the firewall during workflow execution:
>
> - `bun.sh`
>> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "bun.sh"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [CI Failure Doctor](https://github.com/githubnext/tsessebe/actions/runs/25838634503) · ● 28.3M · [◷](https://github.com/search?q=repo%3Agithubnext%2Ftsessebe+is%3Aissue+%22gh-aw-workflow-call-id%3A+githubnext%2Ftsessebe%2Fci-doctor%22&type=issues)
>
> To install this [agentic workflow](https://github.com/githubnext/agentics/blob/c7d030cd6d4607b90d9ac3ffc8b24aff4f251632/workflows/ci-doctor.md), run
> ```
> gh aw add githubnext/agentics/workflows/ci-doctor.md@c7d030cd6d4607b90d9ac3ffc8b24aff4f251632
> ```

Start with .github/workflows/ci.yml and inspect the Bun version used by the failing Test & Lint job, comparing it with local Bun 1.3.14. Review or rerun the linked workflow and confirm that `bun test --coverage ./tests/` passes in CI after the version is made deliberate.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.