scripts/runner: pass TEST_SERIAL_ID for proper parallelism handling

[nektro]

adds environment variable for proper tmpdir setup
actual fix for d2a4fb8 (which was reverted)
this fixes flakyness in node:fs and node:cluster when using scripts/runner.node.mjs locally with the --parallel flag

[robobun]

^{Updated 6:14 PM PT - Oct 5th, 2025}

❌ @nektro, your commit c62b9db has some failures in Build #28101 (All Failures)

---

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• scripts/runner.node.mjs (6 hunks)

🧰 Additional context used

🧠 Learnings (13)

📓 Common learnings

Learnt from: CR
PR: oven-sh/bun#0
File: test/CLAUDE.md:0-0
Timestamp: 2025-09-03T17:10:13.486Z
Learning: Applies to test/**/*.test.ts : When spawning Bun in tests, use `bunExe()` and `bunEnv` from `harness`

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/cli/**/*.{js,ts} : When testing Bun as a CLI, use spawn with bunExe() and bunEnv from harness, and capture stdout/stderr via pipes

Learnt from: CR
PR: oven-sh/bun#0
File: test/CLAUDE.md:0-0
Timestamp: 2025-09-03T17:10:13.486Z
Learning: Applies to test/**/*.test.ts : Do not set explicit test timeouts; rely on Bun’s built-in timeouts

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/js/node/test/** : Vendored Node.js tests under test/js/node/test/ are exceptions and do not follow Bun’s test style

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/**/*.{js,ts} : Write tests in JavaScript or TypeScript using Bun’s Jest-style APIs (test, describe, expect) and run with bun test

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-08-30T00:09:39.100Z
Learning: Applies to test/bake/bake-harness.ts : Provide and maintain shared test utilities: devTest, prodTest, devAndProductionTest, Dev, Client, and helpers in the harness

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/**/*.{js,ts} : Use shared utilities from test/harness.ts where applicable

Learnt from: CR
PR: oven-sh/bun#0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-09-08T00:41:12.052Z
Learning: Follow existing patterns in similar V8 classes, add comprehensive Node.js parity tests, update all symbol files, and document any special behavior

📚 Learning: 2025-08-30T00:12:56.803Z

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/cli/**/*.{js,ts} : When testing Bun as a CLI, use spawn with bunExe() and bunEnv from harness, and capture stdout/stderr via pipes

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-09-03T17:10:13.486Z

Learnt from: CR
PR: oven-sh/bun#0
File: test/CLAUDE.md:0-0
Timestamp: 2025-09-03T17:10:13.486Z
Learning: Applies to test/**/*.test.ts : When spawning Bun in tests, use `bunExe()` and `bunEnv` from `harness`

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-08-30T00:12:56.803Z

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/js/node/test/** : Vendored Node.js tests under test/js/node/test/ are exceptions and do not follow Bun’s test style

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-09-08T00:41:12.052Z

Learnt from: CR
PR: oven-sh/bun#0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-09-08T00:41:12.052Z
Learning: Follow existing patterns in similar V8 classes, add comprehensive Node.js parity tests, update all symbol files, and document any special behavior

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-09-03T17:10:13.486Z

Learnt from: CR
PR: oven-sh/bun#0
File: test/CLAUDE.md:0-0
Timestamp: 2025-09-03T17:10:13.486Z
Learning: Applies to test/**/*.test.ts : Do not set explicit test timeouts; rely on Bun’s built-in timeouts

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-08-30T00:12:56.803Z

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/**/*.{js,ts} : Write tests in JavaScript or TypeScript using Bun’s Jest-style APIs (test, describe, expect) and run with bun test

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-09-03T17:10:13.486Z

Learnt from: CR
PR: oven-sh/bun#0
File: test/CLAUDE.md:0-0
Timestamp: 2025-09-03T17:10:13.486Z
Learning: Applies to test/**/*.test.ts : Import common test utilities from `harness` (e.g., `bunExe`, `bunEnv`, `tempDirWithFiles`, `tmpdirSync`, platform checks, GC helpers)

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-09-03T17:10:13.486Z

Learnt from: CR
PR: oven-sh/bun#0
File: test/CLAUDE.md:0-0
Timestamp: 2025-09-03T17:10:13.486Z
Learning: Applies to test/**/*.test.ts : Name test files `*.test.ts` and use `bun:test`

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-08-30T00:12:56.803Z

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-08-30T00:12:56.803Z
Learning: Applies to test/js/bun/**/*.{js,ts} : Place Bun API tests under test/js/bun/, separated by category (e.g., test/js/bun/glob/)

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-09-08T04:44:59.101Z

Learnt from: CR
PR: oven-sh/bun#0
File: CLAUDE.md:0-0
Timestamp: 2025-09-08T04:44:59.101Z
Learning: Applies to test/**/*.test.{ts,tsx} : Avoid shell commands (e.g., find, grep) in tests; use Bun.Glob and built-ins instead

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-08-30T00:09:39.100Z

Learnt from: CR
PR: oven-sh/bun#0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-08-30T00:09:39.100Z
Learning: Applies to test/bake/dev/bundle.test.ts : bundle.test.ts should contain DevServer-specific bundling tests

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-09-20T03:39:41.770Z

Learnt from: pfgithub
PR: oven-sh/bun#22534
File: test/regression/issue/21830.fixture.ts:14-63
Timestamp: 2025-09-20T03:39:41.770Z
Learning: Bun's test runner supports async describe callbacks, unlike Jest/Vitest where describe callbacks must be synchronous. The syntax `describe("name", async () => { ... })` is valid in Bun.

Applied to files:

• scripts/runner.node.mjs