🤖 fix: prevent mux-server crash on task timeout + undici termination

[ibetitsmike]

Problem

When a tool call (notably task) times out waiting for agent_report, the parent stream can hit an undici BodyTimeoutError surfaced as TypeError: terminated. This could bubble into an unhandled rejection or uncaught exception, taking down mux-server.

Error observed:

src/node/services/streamManager.ts:1146 Tool execution error for 'task' {
  error: Error: Timed out waiting for agent_report
      at Timeout.<anonymous> (/tmp/mux/npm/node_modules/mux/src/node/services/taskService.ts:854:18)
}

TypeError: terminated
    at Fetch.onAborted (node:internal/deps/undici/undici:11132:53)
    ...
  [cause]: BodyTimeoutError: Body Timeout Error { code: 'UND_ERR_BODY_TIMEOUT' }

Solution

Multi-layered defense to ensure server stays up:

1. Suppress side-promise unhandled rejections: streamText() returns fullStream (consumed in try/catch), plus side promises (usage, steps, providerMetadata, etc.). When aborted/terminated, these can reject without handlers → crash. Now we attach no-op .catch() to each.

2. Treat abort-induced errors as cancellation: If stream was aborted/stopping when an error occurs (like TypeError: terminated), don't set ERROR state or write error partial - just log at debug level and proceed to cleanup.

3. Safe tool-error formatting: The tool-error handler did JSON.stringify(error) which can throw (circular refs, BigInt). Wrapped in try/catch with fallback.

4. task tool timeouts → running status: When waitForAgentReport times out, return {status:"running"} instead of throwing - consistent with task_await behavior. This prevents timeouts from becoming tool execution errors.

5. Improve undici error categorization: Detect TypeError: terminated and UND_ERR_BODY_TIMEOUT and map to "network" instead of "unknown".

6. Safety net handlers: Add process.on("uncaughtException"/"unhandledRejection") in CLI server that suppress benign network errors and keep the server running.

Testing

• make typecheck - passes
• make lint - passes
• make fmt-check - passes
• bun test src/cli/server.test.ts - 13 pass
• bun test src/node/services/streamManager.test.ts - 7 pass, 2 skip

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