Automatic session titles reworked with fallbacks and fewer duplicates

What

Claude Code names each session automatically by asking the model for a title. That process was reworked:

• The request (now requestSessionTitle, replacing generateSessionTitle) returns one of three results: titled, with the title; unusable; or failed. Before, it returned a title or nothing.
• An API error now raises 'Session title request failed with an API error'. The log line changed from generateSessionTitle failed to requestSessionTitle failed.
• A fallback title is kept per session for a limited number of unusable replies and merged with the result.
• Turns that continue automatically are handled, and titling is skipped when a new check passes.
• Whether the content is a slash command is now decided from the commands that dispatch slash commands, instead of a known-command check.
• The generate_session_title control request waits for a pending title for the same session instead of starting a second one.
• A pending title request that is withdrawn is cancelled.
• On resume or rewind, the fallback and the pending request are cleared, and after a rewind with a request in flight a title may be generated again.

Why

Session titles should appear more reliably, duplicate title requests are avoided, and a resumed or rewound session no longer keeps an out-of-date title.