fix(mcp): keep stdio child no-proxy entries runtime-safe

[hydraxman]

Related Issue

Fixes #1931

Problem

When an HTTP proxy is configured, stdio MCP children inherit [::1] in both NO_PROXY casings. Python httpx treats that entry as an invalid port and exits before the MCP handshake. Removing it unconditionally would instead regress Node's IPv6 loopback bypass when NODE_USE_ENV_PROXY=1.

What changed

• pass the stdio command and arguments into child environment construction in both agent engines
• keep [::1] for direct and commonly wrapped Node launchers and JavaScript entry points
• emit the portable bare ::1 form for other runtimes, while honoring explicit parent or per-server bracketed overrides
• add a patch changeset and regression coverage for portable, Node, wrapped-Node, and explicit-override paths

No documentation update is needed because the public proxy configuration and precedence are unchanged.

Testing

• pnpm exec vitest run test/mcp/client-stdio.test.ts in packages/agent-core — 29 passed
• pnpm exec vitest run test/agent/mcp/client-stdio.test.ts in packages/agent-core-v2 — 20 passed
• pnpm --filter @moonshot-ai/agent-core test — 3,990 passed, 3 expected failures, 30 skipped, 1 todo
• pnpm --filter @moonshot-ai/agent-core-v2 test — 3,958 passed
• typecheck for both agent-core packages — passed
• changed-file type-aware lint — 0 warnings, 0 errors
• root pnpm lint — 0 errors (existing warnings only)
• Python httpx.Client() reproducer — bracketed child value fails; portable child value succeeds
• Node 24.15 local IPv6 fetch with an unreachable proxy — bracketed Node value returns 200 ok; bare value attempts the proxy and fails

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: 8edaf4a

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

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Patch

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