feat(core): interrupt v2 session execution (#30850)

specs/v2/session.md

@@ -18,6 +18,13 @@ sessions.prompt({ id?, sessionID, prompt, delivery?, resume? })
   -> exact retry schedules another wake unless resume is false
   -> resume omitted or true schedules execution after admission
   -> resume false admits only
+
+sessions.interrupt(sessionID)
+  -> interrupts the active ownership chain on this process
+  -> waits for active drain cleanup and settlement
+  -> suppresses reruns already queued before interruption
+  -> preserves durable inbox rows for a later fresh wake or resume
+  -> idle or missing Session is a no-op
 ```
 
 `session_input` is the durable admission inbox. Admitted inputs remain outside model-visible Session history until the serialized runner publishes `PromptLifecycle.Promoted`. The projector atomically writes the visible user message and marks its inbox row promoted in the same event transaction. The legacy V1-to-V2 shadow bridge continues publishing ordinary `Prompted` events for already-visible V1 prompts.
@@ -141,7 +148,7 @@ Execution has two entry points:
 
 Post-crash activity recovery is intentionally deferred. A wake does not infer that ambiguous provider work is safe to retry after an input has already been promoted. Explicit `run` may deliberately continue from durable projected history. A future recovery slice should model durable activity identity, provider-dispatch ambiguity, required continuation, queue-opener reservation, retry policy, and visible recovery status together.
 
-A location-scoped `SessionRunCoordinator` serializes each Session drain chain while allowing different Sessions to drain concurrently. Automatic startup discovery, durable multi-node ownership, stale-owner fencing, interruption controls, and retry policy remain future work.
+A process-global `SessionRunCoordinator` serializes each local Session drain chain while allowing different Sessions to drain concurrently. It enters the Session's current Location only when a drain starts, so interruption targets process execution ownership rather than Location cache identity. Interruption establishes a local ownership-chain boundary by stopping the current chain while preserving pending/unpromoted durable inbox rows for a later fresh wake and projected history for explicit resume. A Location runner also fences every new provider turn against its captured Location so a moved Session cannot begin another turn through source-Location tools or context. An already-dispatched provider turn may still settle source-Location calls until a future move-control slice interrupts active ownership. Automatic startup discovery, durable multi-node ownership, stale-owner fencing, and retry policy remain future work.
 
 Inbox promotion coalesces pending steers in durable admission order and opens one queued activity at a time in FIFO order. Add explicit inbox backlog and steering-batch limits before exposing broad multi-caller admission or untrusted queue growth.
 

specs/v2/todo.md

@@ -33,7 +33,7 @@ through legacy `SessionPrompt.loop(...)`:
 Prompt admission now uses a durable `session_input` inbox rather than immediate
 transcript projection. `steer` inputs coalesce into the active activity at the
 next safe provider-turn boundary. `queue` inputs form a FIFO of future activities
-that open one at a time. A location-scoped `SessionRunCoordinator` coalesces process-local wakeups
+that open one at a time. A process-global `SessionRunCoordinator` coalesces process-local wakeups
 around settlement races. Explicit `run` resumes perform at least one provider
 attempt; advisory `wake` notifications call the provider only for eligible inbox
 work. Steers coalesce into the active activity at
@@ -55,7 +55,7 @@ Next reviewed slices:
 - integrate the new BackgroundJob service with V2 tool execution: support background
   bash jobs and background agent dispatch with durable status observation,
   completion delivery, and explicit cancellation / continuation semantics
-- add compaction, interruption, retries, and stale-owner fencing
+- add compaction, durable/clustered interruption, retries, and stale-owner fencing
   only as their slices become concrete
 
 ### Deferred durable activity recovery