CLI --completion crashes on an unhandled EPIPE when its reader closes early #2646

Problem

Found during the v2.10.0 release smoke (#2623) and recorded in its ledger. mcp-inspector --cli --completion <shell> writes the script through awaitableLog. If the reader closes the pipe before the write finishes, Node throws an unhandled 'error' event (write EPIPE) with a stack trace. Two cases do this: | head, and bash 3.2's source <(…), where process substitution does not keep the pipe open.

Reproduce

node clients/launcher/build/index.js --cli --completion bash | head -1
# → node:events … Unhandled 'error' event … Error: write EPIPE

Expected

The completion path treats EPIPE on stdout as a normal early close and exits quietly. Other paths already do this (mcpdo's auth helper installs process.stdout.on("error", () => {})).

Priority

Low (rubric total 5): Severity 2, Urgency 1, +1 bug, +1 milestoned.