feat(think): make platform tools native to code

[mattzcarey]

Summary

• make Think's built-in code tool a durable Code Mode runtime while keeping read, write, edit, and code as the four built-in model tools
• expose Think platform capabilities inside code as workspace.*, context.*, skills.*, extensions.*, fetch.*, and one namespace per connected MCP server
• separate MCP connection registration from direct model-tool exposure: Think no longer calls mcp.getAITools() while assembling a turn
• cache explicit MCPClientManager.getAITools() conversion by live connection, server id, and catalog revision, without scattered invalidation branches
• make Code Mode runtime ownership explicit: applications using custom bash, custom code, or createExecuteTool(this) set readonly codeTool = false
• add Worker Loader defaults, migration docs, an updated coding starter, and a focused examples/think-codemode-mcp app

Why

Issue #1938 reproduces with a 313-tool MCP server. A normal Think turn currently calls getAITools() before activeTools filtering, recursively converting 626 input/output JSON Schemas into Zod graphs even when the application intends to use MCP only through Code Mode.

The regression registers 313 complex MCP tools, replaces getAITools() with a throwing/counting trap, and completes this flow through the real Durable Object transport and Dynamic Worker runtime:

1. codemode.search() finds catalog.echo
2. codemode.describe() generates its types on demand
3. catalog.echo() executes over MCP RPC
4. the model still receives only four built-in schemas
5. getAITools() is called zero times

A separate MCP manager regression verifies that filtered and unfiltered getAITools() calls share converted schemas. Replacing the connection, changing its id, or replacing its catalog causes conversion exactly once for the new revision.

Compatibility boundary

This is a pre-1.0 minor change for @cloudflare/think:

• the built-in tool is named code and accepts { code: string }; it does not accept POSIX shell syntax or the legacy { script, cwd } payload
• readonly codeTool = false opts out of the built-in runtime and restores the direct workspace, context, skills, extensions, and fetch layout
• custom bash, custom code, and createExecuteTool(this) do not opt out implicitly; Think rejects competing runtime owners with an actionable error
• legacy workspaceBash configuration moves to codeTool or an explicit createWorkspaceTools() tool set
• application getTools(), Think actions, and client tools remain direct because they have separate lifecycle and approval semantics
• the built-in runtime requires worker_loaders: [{ binding: "LOADER" }]; generated Think config includes it, and custom Worker entries export CodemodeRuntime through @cloudflare/think/server-entry
• the standalone createWorkspaceTools().bash remains a real just-bash POSIX shell

Structural audit

• replaced the MCP manager's server-id cache and reconnect/rename/close invalidation branches with a WeakMap keyed by the live connection
• removed runtime-handle identity inference from Think; codeTool is the sole ownership policy
• moved the Workspace filesystem capability guard into @cloudflare/shell and deleted Think's duplicate adapter module
• moved namespaced StateConnector type rendering into Shell's prompt module
• replaced Think's string rewrite of the Agent Skills prompt with an explicit activation-guidance seam
• rebuilt the native runtime after hibernation using the same MCP wait policy as inference

Verification

• pnpm run build: all 26 targets passed
• pnpm run check: exports, formatting, lint, and all 118 TypeScript projects passed
• pnpm exec nx affected -t test --base=origin/main: all 19 affected projects passed
• Agents: 2,280 tests passed
• AI Chat: 728 tests passed
• Code Mode: 373 tests passed
• Shell: 251 passed, 1 skipped
• Think: 923 Worker, 10 generated-entry, 10 Vite, 55 CLI, and 5 React tests passed
• agent-think: 37 tests passed
• focused MCP example production build passed

Fixes #1938

[changeset-bot]

🦋 Changeset detected

Latest commit: 44e1c31

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
agents	Patch
@cloudflare/think	Minor
@cloudflare/codemode	Patch
@cloudflare/shell	Patch
@cloudflare/agent-think	Patch

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commit: 44e1c31

[devin-ai-integration]

✅ Devin Review: No Issues Found

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