[ThomasK33]

Why

The advisor on #313 found three ways an RPC error response can still break, and the operator wants them shipped now:

1. RpcServer starts each request with void this.processRequestLine(...). If building or sending the response throws, the rejection is unhandled. Node then ends the host process, and the session ends failed.
2. fix: carry CliError details across the session host RPC #313's sendableDetails keeps any JSON. A toJSON can turn details into undefined, a string or an array. undefined makes serialized.length throw. A string or an array fails RpcResponseSchema, so the server's invariant throws. Both become the unhandled rejection in point 1.
3. The server sends a CliError message of any length. A 1.1 MB message gives "RPC response exceeds maximum buffer size." at the CLI instead of the error's code. main has the same gap, for CliError and for other errors.

What changed

• src/host/rpcServer.ts:
  • A .catch on processRequestLine logs the error with console.error and answers RPC_ERROR "RPC request handling failed unexpectedly." with the request's id. The host keeps running.
  • sendableDetails keeps details only when JSON.stringify gives a string of at most 65,536 characters that parses to a plain object.
  • sendableMessage cuts an error message to 65,536 characters, ending with [message truncated]. Both RPC_ERROR responses and CliError responses use it.
  • A module-load invariant checks that a message and details at their caps fit in one response, even when every character is a control character (6 characters in JSON).
• src/host/README.md describes the message cap and the unexpected-failure answer.

Behavior changes for CLI and JSON users

• An error with a message over 65,536 characters now keeps its code, and its message ends with [message truncated]. Before, the CLI reported exit 9 RPC_ERROR "RPC response exceeds maximum buffer size.".
• A failure inside the host's response building now gives exit 9 RPC_ERROR "RPC request handling failed unexpectedly." Before, the host process crashed and the session ended failed.
• The envelope shape and the error codes do not change.

The host's stdio is 'ignore', so the console.error line shows only when the host runs in the foreground, for example in tests.

Verification

• Red first (434eb90), on main e7c7e1d (fix: carry CliError details across the session host RPC #313 merged): in test/unit/host/rpcServer.test.ts, a real RpcServer and the real sendRpc over a Unix socket.
  • toJSON returning undefined, a string or an array: test timeout, and Vitest reports the unhandled rejections (TypeError: Cannot read properties of undefined (reading 'length'), and twice RPC CliError response must satisfy RpcResponseSchema.).
  • An error whose message getter throws: test timeout and an unhandled rejection.
  • A 1,100,000-character CliError message, and the same message on a plain Error: "RPC response exceeds maximum buffer size.".
  • The throwing-getter details case passes on e7c7e1d and stays covered.
• Green (bc36097, docs 74a2e47): vitest run test/unit/host/rpcServer.test.ts test/unit/host/rpcClient.test.ts: 26 passed. vitest run test/unit: 1949 passed.
• tsc --noEmit, oxlint src test vitest.config.ts and oxfmt --check pass.

Refs #313

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Generated with xum • Model: anthropic:claude-opus-5-5 • Thinking: xhigh

[ThomasK33]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-04T02:41:06.572575Z	74a2e47	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

Reviewed commit: 74a2e47ad7

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