fix(tools): support streamable HTTP MCP app routes

[drewstone]

What changed

• Make every handleAppToolRequest endpoint speak stateless Streamable HTTP MCP JSON-RPC through the existing shared MCP handler.
• Preserve the direct HTTP args/arguments/bare-body contract and custom app-tool dispatch.
• Accept params.arguments in the shared argument reader for routes that need raw-argument inspection.
• Add buildProductEgressPolicy(publicOrigin, extraDomains) so product shells declare one consistent strict sandbox policy.
• Regenerate the package API/codemap docs.

Why

A real Legal production chat reached the sandbox after the billing/egress fix, but every app-tool MCP route returned 400/500 because OpenCode sent JSON-RPC envelopes to routes that only understood direct tool bodies. This moves the protocol translation into agent-app once.

Proof

• pnpm vitest run src/tools/auth.test.ts src/tools/registry.test.ts src/sandbox/index.test.ts — 248 passed.
• pnpm vitest run tests/sequences/mcp-server.test.ts tests/design-canvas/mcp-handler.test.ts src/sandbox/index.test.ts tests/codemap-fresh.test.ts --no-file-parallelism — 304 passed.
• pnpm typecheck — passed.
• pnpm docs:gen — passed.
• git diff --check — passed.
• pnpm build emitted a successful ESM build but its DTS worker exceeded the local memory limit; typecheck passed independently.

[tangletools]

✅ Auto-approved drewstone PR — 88b82b80

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-08-04T05:05:01Z}