Harden local CLI IPC against oversized requests and indefinite waits

Problem

The local CLI protocol uses UDP with several failure modes:

• The CLI uses assert! when the serialized request exceeds MAX_REQUEST_SIZE, so a long user-controlled query or field can panic the process.
• Connection and response reads have no deadline, so a nonresponsive client can block a command indefinitely.
• Large responses are split into UDP datagrams without request IDs, sequence numbers, retries, or an integrity check.

The loopback interface reduces packet-loss risk, but it does not prevent a stalled server, oversized input, or protocol desynchronization.

Expected behavior

CLI commands should either return a valid response or fail with a bounded, actionable error. User input should never trigger an assertion panic.

Suggested approach

A length-prefixed local stream protocol would provide the strongest guarantee. A smaller first step could add request-size errors, read deadlines, request IDs, and sequenced response chunks.

Acceptance criteria

• Oversized requests return a normal error.
• Connection and response waits have configurable or documented deadlines.
• Missing or incomplete response chunks fail cleanly.
• Concurrent CLI clients cannot mix responses.
• Tests cover a missing server, a stalled server, oversized input, and multi-chunk responses.