Feature request: Auto-generate session titles after initial messages

Summary

Currently, session titles in the /resume picker are set to the first user prompt, which is often a truncated, context-lacking string. It would be great to have an option to auto-generate a meaningful session title after a configurable number of messages (e.g., 3–5), similar to how ChatGPT auto-names conversations.

Motivation

When you accumulate many sessions, the first-prompt-as-title approach makes it hard to find past conversations. Manually running /rename is easy to forget, and by the time you realize you should have named a session, it's often already lost in the list.

Proposed solution

A setting like:

{
  "autoTitleAfterMessages": 3
}

After N messages, Claude would automatically generate a short, descriptive title for the session based on the conversation so far (e.g., "Refactor auth middleware", "Debug flaky test in CI").

Alternatives considered

• Hook-based approach: A UserPromptSubmit hook that triggers a rename after N messages — but hooks currently have no way to feed a /rename command back into the session.
• Manual /rename: Works but is easy to forget and adds friction.

Additional context

• Setting cleanupPeriodDays: 0 makes this more important since users keeping all sessions indefinitely will accumulate a lot of generically-named entries.
• The title generation could reuse the same summarization logic that would be used for conversation compression.