feat(ai-code-mode, ai-harness): code mode for harnesses with pluggable isolates

[AlemTuzlak]

Add codeMode({ driver }) to a harness, and the model gets one execute_typescript tool. It writes one TypeScript program that calls several tools, and the program runs in the isolate you pick: QuickJS, Node, Cloudflare, or Daytona. Read-only tools move into code mode, including MCP tools found after /connect. Tools that need approval stay normal tool calls.

Stacked on #1523 (Phase 7) → #1522 → #1521 → #1520 → #1519 → #1518 → #1515 → #1513 → #1509. Merge those first.

🎯 Changes

• codeMode at @tanstack/ai-code-mode/harness: a harness plugin. driver takes any @tanstack/ai-isolate-* driver. The other createCodeMode options pass through.
• Which tools move: tools with execute that do not set needsApproval and that the permission rules allow in plan mode (file reads, read-only MCP tools). include picks the tools yourself. A call inside the isolate does not stop for approval, so edits and commands stay out.
• Safe names: MCP tool names like notion-search are not JavaScript identifiers. The plugin gives code mode a copy named notion_search. If two names clash, the second tool stays a direct tool.
• prepareTools plugin hook in @tanstack/ai-harness: change the tool list of each turn, after discoverTools and before prompts resolve.
• PermissionRules and decidePermission are also exported from the @tanstack/ai-harness root, because ./plugins is Node only and code mode stays edge-safe.
• examples/harness-cli turns on code mode with the QuickJS driver.
• Docs: docs/harness/code-mode.md (new). Changeset: ai-code-mode, ai-harness (minor).

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested code changes locally with pnpm run test:pr, or these tests do not apply to this pull request.
• I fully understand the code in this pull request, including any code generated with AI assistance.
• Docs: I updated docs/ for this change, or this change is not user-facing.
• Changeset: I added a changeset (pnpm changeset), or this PR does not change a published package.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

Testing

Commands run (not the full pnpm test:pr, see below):

• @tanstack/ai-code-mode: vitest run (153 passed), test:types, publint --strict. New: tests/harness.test.ts (tools move behind execute_typescript, discovered MCP tools included, approvals and edits kept, include, no match, safe names and clashes).
• @tanstack/ai-harness: vitest run (147 passed), test:types. New: tests/prepare-tools.test.ts.
• examples/harness-cli: tsc --noEmit.
• kiira check docs/harness/code-mode.md, oxfmt, oxlint on the changed files.
• Skipped the full pnpm test:pr because it is slow on this machine. CI runs it. No new E2E test: the tests use a stand-in isolate, and the manual run below used the real QuickJS driver.

Manual test (done with real accounts)

1. Do steps 1 and 2 of the Phase 7 manual test (build, .env, /connect linear, /connect notion).
2. Ask: in one execute_typescript program, list my Linear issues and search Notion for "Teams CLI", then summarize.
3. Result on my run: one program ran in QuickJS in 1.5 seconds, called external_linear_list_issues and external_notion_notion_search, and the answer used both results.

How this PR makes testing easy

• packages/ai-code-mode/tests/harness.test.ts and packages/ai-harness/tests/prepare-tools.test.ts.
• examples/harness-cli runs code mode with the QuickJS driver.

Risk / rollback

Low. A new subpath and a new plugin hook. Code mode is opt-in. Revert the PR to undo.

Public API change

Before

defineHarness({ name: 'acme/assistant', adapter, plugins: () => [linear] })

After

import { codeMode } from '@tanstack/ai-code-mode/harness'
import { createQuickJSIsolateDriver } from '@tanstack/ai-isolate-quickjs'

defineHarness({
  name: 'acme/assistant',
  adapter,
  plugins: () => [linear, codeMode({ driver: createQuickJSIsolateDriver() })],
})

🤖 Generated with Claude Code

https://claude.ai/code/session_01APYv1qshKyjPPpkFyRZhfZ

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☁️ Nx Cloud last updated this comment at 2026-09-26 15:04:59 UTC

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