V2: auto-resume active sessions after server restart

[opencode-agent]

Summary

V2 sessions that were actively executing should automatically continue after the shared server restarts, instead of requiring the user to manually prompt them again or leaving stale in-progress state in the TUI.

Desired Behavior

On server startup:

1. Identify sessions whose execution was active when the previous process stopped.
2. Reconcile the interrupted step and any in-flight tool parts to durable terminal state.
3. Resume the agent loop from persisted session state.
4. Notify connected clients so the TUI converges without a reload.

The recovery path must not blindly re-execute an in-flight side-effecting tool. A tool whose completion cannot be proven should be recorded as interrupted; the resumed model turn can then inspect state and decide how to continue.

Acceptance Criteria

• An active V2 session automatically resumes after a normal daemon restart, upgrade restart, or unexpected process exit.
• Persisted running/pending tool parts are settled before continuation; no stale spinners remain.
• Recovery does not automatically replay an ambiguous side-effecting tool call.
• Exactly one process owns the resumed execution, including when multiple clients reconnect concurrently.
• Connected and later-opening clients converge on the resumed canonical session state.
• Recovery is idempotent across repeated crashes/restarts.
• Tests cover restart during model streaming, restart during a read-only tool, restart during a side-effecting tool, and repeated restart while recovering.

Related Work

• V2: port transform and interruption durability across both model paths #35467 defines interruption durability and terminalization across restart/replay.
• V2: interrupted work remains spinning after machine restart #35642 records the current user-visible symptom: interrupted work remains spinning after a machine restart.
• V2: reconnecting clients can restart-loop the shared daemon #35448 covers restart authority and daemon restart loops, which must not create duplicate recovery owners.

This issue adds the continuation policy after durable interruption reconciliation; it does not replace those issues.

Source

• Request: https://discord.com/channels/1391832426048651334/1447692703549755466/1523871474052763749
• James volunteered to own it and Dax agreed: https://discord.com/channels/1391832426048651334/1447692703549755466/1523871274634317966