Directory sync waits more simply before a turn and records turns that run before sync is ready

What

Directory sync keeps a session's files in step with another machine. Several of its internals changed:

• Before each turn, it no longer waits in several polling loops with timeouts. It now waits for the sync pass or for the turn to be cancelled, whichever comes first.
• When a turn runs before sync is ready ("armed"), it writes a marker file, unarmed-turn-${sessionId}.json, into the session's state.
• pullPoint, the step that pulls changes in, dropped its retry loops and now makes a single attempt. Its reporting can now record a read_failed result.

Why

This may change how long a turn is held while waiting for files to arrive. Turns that start before sync is ready are now tracked instead of going unrecorded.