fix(coding-agent): evict empty drafts when the last direct viewer detaches (ENG-5831)

[snimu]

Problem

Starting the TUI and quitting right away leaves the empty draft session behind as a zombie row in the agents view until an idle sweep catches it, if one ever runs (ENG-5831).

The empty-draft eviction from #1920 runs when the supervisor sees a client's last detach: on a supervisor socket close it walks that socket's attached sessions and evicts abandoned empty drafts. #1926 moved attach and detach onto the direct worker transport, so the session's viewer now attaches and detaches on the worker's own socket. The supervisor socket never records the attachment, its close-time walk finds nothing, and a clean quit does not touch the supervisor at all.

Fix

The worker already reports the exact signal: since #1926 it flushes a roster update when a direct viewer attaches or detaches, and that summary carries directAttachedClients. Both exit paths produce it — a clean detach command and an unclean socket drop share the worker's detach path.

The supervisor's roster write funnel now triggers the existing last-detach eviction when a worker-reported summary's directAttachedClients drops to zero. The eviction candidate check also counts direct viewers through the shared attachment sum, so with one routed and one direct client the session is evicted only when the last of both is gone, in either order.

No new wire frames, timers, or sweep changes: the fix reuses the roster signal and the eviction path that already exist.

Validation

• New pins in daemon-supervisor-eviction.test.ts: a worker-reported drop to zero direct viewers evicts an empty draft; a mixed routed+direct session evicts only after the last of both detaches.
• Existing fix(coding-agent): honest status and prompt eviction for empty sessions #1920 eviction pins, daemon-peer-transport, agent-connection-daemon, daemon-supervisor-monitor, and daemon-routed-client suites all green with sanitized env.
• Root npm run check green.

Linear: ENG-5831

Note

Evict empty drafts when last direct-attached viewer detaches in DaemonSupervisor

• Updates the evictable-empty-worker check to use attachedClientCount so it accounts for both supervisor-routed and direct-attached clients when deciding if a worker is evictable
• In writeRosterEntry, detects when a worker's directAttachedClients transitions from >0 to 0 and triggers evictEmptySessionOnLastDetach, aligning direct-transport detach behavior with supervisor-routed clients
• Adds tests covering eviction on last direct detach and the mixed client-kind case where eviction only fires after both routed and direct clients are gone

^{Macroscope summarized 2f879e6.}

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Note

Medium Risk
Touches daemon session eviction and roster-driven lifecycle, but reuses existing eviction helpers and is covered by new unit tests rather than new wire protocol.

Overview
Fixes empty draft sessions sticking around in the agents list after a user opens the TUI and quits immediately, because viewers on the direct worker transport no longer detach through the supervisor socket.

When a worker roster update shows directAttachedClients dropping from above zero to zero, writeRosterEntry now runs the same evictEmptySessionOnLastDetach path used for supervisor-routed clients (clean detach or socket drop both show up this way). The empty-worker eviction check uses attachedClientCount so routed and direct attachments are counted together—mixed sessions are only evicted after both kinds of viewer are gone.

Adds eviction tests for last direct detach and routed+direct ordering; changelog note for ENG-5831.

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