Server-side conversation threads gain a 'drop and recreate' path

What

• The internal planner that decides whether to continue an existing server-side conversation thread or start a new one gained a new input, dropHeldStateless, and a new reason code, thread_minted_drop, for when a thread is dropped and a new one is created in its place.
• New outcome telemetry fields (dropArmed, dropHeldStateless, continuesSinceDropCreate, dropReportUnmatched) were added to the tengu_tether_live_outcome event, and a new tether_drop_recreate counter fires whenever this drop-triggered recreation happens.
• The tengu_tether_decision analytics event also now reports the dropHeldStateless field alongside the existing modelHeldStateless/relayHeldStateless/classifierHeldStateless fields.

Why

This gives Claude Code (and Anthropic's internal monitoring) a documented way to recover when a stateless server-side thread needs to be dropped and replaced, with telemetry to track how often and how it happens.