2026-08-22 -- HUB-1: AbortOpenTurn, the one non-clean turn-exit cleanup

The last High finding of the Phase 1 review: turn-end cleanup was scattered across four terminal paths, and the newest path (the silence backstop) had forgotten most of it.

The defect

A turn holds open: the streaming message + running tool/subagent records, a possible pending permission card, the UapTurnScope (one Undo group + the AssetDatabase auto-refresh suppression window), the per-turn non-undoable warning set, the scripts-commit attribution flag, and (for continuation turns) SessionStateBridge.AutoContinueTurnIsContinuation.

Only OnTurnCompleted — a clean ResultMessage — released all of it. The other exits each hand-picked a subset:

path	had	missing
OnTurnStalled	Finalize	scope, permission, warning set, attribution, continuation flag
OnStateChanged(Errored)	scope, continuation flag	Finalize, permission, warning set, attribution
OnProcessDied	Finalize, permission, continuation flag	scope*, warning set, attribution
TearDownClient	everything except	continuation flag (correctly — see below)

(*covered indirectly by the Errored transition when it fires.)

The worst case was the stall: TurnTracker.EndTurn runs BEFORE TurnStalled is raised, so the stalled turn can never reach OnTurnCompleted — yet the handler only finalized the streaming message. The UapTurnScope leak left AssetDatabase auto-refresh disallowed (and the Undo group open) for the rest of the editor session (the finding’s headline symptom), the stalled turn’s non-undoable warning attached itself to the next unrelated turn, a pending permission card stayed up unanswerable, and a stalled continuation turn stranded the continuation flag (defect 5’s mechanics through a path defect 5 never covered). The crash-loop-suspended branch had the same “no teardown ever follows” exposure for the warning set and attribution flag.

The project’s own defect history (4, 5, 6) is a list of “a new terminal path forgot one clear” — the roadmap ordered this consolidation before any further terminal-path work for exactly that reason.

The fix

AgentHub.AbortOpenTurn(bool clearContinuationFlag) performs all of the above, idempotently (several terminal paths legitimately fire for one exit: ProcessDied AND the Errored transition AND an eventual teardown). All four paths now call it and nothing else hand-picks clears.

clearContinuationFlag semantics (the review’s flagged foot-gun):

• true — stall/errored/died: the turn will never complete, a stranded flag makes the next human-prompted turn refuse to arm auto-continue.
• false — teardown: TearDownClient underlies ShutdownForReload, which runs on the very domain reload the flag exists to survive.

Kept intentionally: the duplicate cleanup in BOTH the Errored transition and OnProcessDied (each covers exits the other misses); TearDownClient’s early UapTurnScope.EndIfActive before the client dispose (the release must not depend on dispose succeeding); _taskIdToToolUseId’s full clear stays teardown-only (death/stall demotion prunes open entries already).

Behavioral upgrades riding along:

• Teardown now FINALIZES the streaming message (blocks marked not-streaming) instead of dropping the reference with the session’s blocks left spinning.
• The errored path drops a pending permission card (previously only the death path did; an Errored-without-death exit left it up).

Tests

AgentHubAbortOpenTurnTests: direct contract (scope release, flag semantics both ways, idempotence) plus wired stall replays through a real AgentClient over FakeCliProcess (SilenceTimeoutSeconds shrunk to force the backstop): the stall releases the scope, clears a continuation flag, and the stalled turn’s non-undoable tools do NOT warn on the next completed turn.