Keep starting byre when one session fails to resume

docs/operations.md

@@ -46,7 +46,7 @@ Agents find closed tasks with the `search_closed_tasks` MCP tool, which task age
 
 - **Request.** `RequestDiscard` records the requester in `discarding_by`, sets `held`, clears any held merge and emits `task.discard_started` (a transcript note). The request returns the still-active task with 202. It is refused (409) while the task is merging or its discard is `held` or `running`; on a `closing` task it retries the cleanup. Merge and holding a merge are refused while `discard_state` is set.
 - **Admission.** While `discard_state` is set, no ordinary turn starts in the task: the store's idle-to-running transition (`transitionSession`) refuses it, so messages, inbox answers, Sync, Compact, queued messages and workflow stage starts all get a conflict and stay queued or held. Queued messages and answers aren't handed over mid-turn either (`deliverMidTurn`). The one way in is `StartDiscardTurn`, which needs `held` and an idle implementer session, and in one transaction sets the session `running`, the state `running` and `discard_session`. byre calls it (`startDiscard` in `internal/agents/summary.go`) right after the request, and again whenever a turn of the task ends with the state `held`; whichever call comes first wins, and a busy session simply leaves the state `held` until its turn ends. It uses the task's live implementer session, or a new one created by the task's creator when there is none, and sends `discardPrompt` (actor `byre`): the task is being discarded, change no files, call `set_task_summary` saying also why it is being dropped, then end the turn. Open inbox questions don't hold it back. If starting the turn fails, byre gives up on the summary: `CloseDiscard` sets `closing` and the task is removed.
-- **Turn end.** Every implementer turn end, in `turnEnded`, on an agent process that exits mid-turn (`pump`), and on a session that can't be resumed at startup, marks the session idle through `EndTurn`, which in the same transaction reports what the discard needs: `closing` when the session is `discard_session` and the state was `running` (it sets `closing`), `held` when a discard is waiting. A turn of the task that ends while a discard is pending takes no snapshot. On `held`, the ending turn's handoff continuation and inbox delivery are skipped and the summary turn starts instead, in the same session, so a turn that was writing a handoff hands the summary turn its full context. On `closing`, `finishDiscard` stops the session, cancels reviews, deletes the snapshot refs, removes the worktree and branch (`git.RemoveWorktree`, which skips whatever is already gone so the cleanup can be repeated), and only then closes the task with `discarding_by` as the actor. The summary turn closes the task however it ends (finished, interrupted, an error), so interrupting it discards without a summary; a summary turn whose process dies discards without a summary too, while an ordinary turn whose process dies while a discard is `held` gets the summary turn started on a new process. A failed cleanup is filed in the task's inbox and leaves the state `closing`.
+- **Turn end.** Every implementer turn end, in `turnEnded`, on an agent process that exits mid-turn (`pump`), and on a session that can't be resumed or sent its restart notice at startup (`failResume`, after which startup carries on with the other sessions; a session whose task can't be loaded is logged as `resume session: load task` and left `running`), marks the session idle through `EndTurn`, which in the same transaction reports what the discard needs: `closing` when the session is `discard_session` and the state was `running` (it sets `closing`), `held` when a discard is waiting. A turn of the task that ends while a discard is pending takes no snapshot. On `held`, the ending turn's handoff continuation and inbox delivery are skipped and the summary turn starts instead, in the same session, so a turn that was writing a handoff hands the summary turn its full context. On `closing`, `finishDiscard` stops the session, cancels reviews, deletes the snapshot refs, removes the worktree and branch (`git.RemoveWorktree`, which skips whatever is already gone so the cleanup can be repeated), and only then closes the task with `discarding_by` as the actor. The summary turn closes the task however it ends (finished, interrupted, an error), so interrupting it discards without a summary; a summary turn whose process dies discards without a summary too, while an ordinary turn whose process dies while a discard is `held` gets the summary turn started on a new process. A failed cleanup is filed in the task's inbox and leaves the state `closing`.
 - **Workflows.** `FinishStage` refuses to mark a stage finished while `discard_state` is set, so a stage whose turn ends after the discard was requested drops its output and doesn't advance. A stage that finished before the request advances as usual (`advanceStage` runs before the summary turn starts, since it reads the worktree's HEAD), and a `closing` task's stage never advances (`nextStage` clears it). An existing stage task being discarded isn't restarted by `advanceTo`.
 - **Restarts.** On startup, a `running` summary turn's session is resumed with `discardRestartPrompt` (the discard prompt again, after a line saying byre restarted) instead of the usual restart notice; `recoverDiscards` then starts the summary turn for each `held` task whose session isn't running, closes each `running` one whose session isn't running, and finishes each `closing` one.
 - **Handoffs.** A handoff continuation (`handoff` in `internal/agents/compact.go`) doesn't start while a discard is pending; it starts the summary turn in the old session instead. It retires the old session only through an idle-to-completed transition, so it can't retire a session the summary turn has just taken, and if a discard arrives between retiring and starting the continuation, the summary turn runs in the new session, without the handoff.