## Why
Replacing a gRPC code-mode runtime loses stored values and running cells. Silently continuing after reconnection hides that loss, while prior external tool operations may already have completed.
## What changed
- Capture the runtime generation when `execute` and `wait` calls are created. If recovery replaces it, reject those calls with an explicit reset error, including concurrent calls and calls first polled after recovery.
- Explain the lost state and advise inspecting prior tool results before retrying. Allow a fresh `exec` call to continue on the replacement runtime.
- Keep `terminate` from reopening the runtime so cleanup cannot hide a reset from the next request.
## Testing
Extend gRPC recovery tests to cover reset errors after host restarts, missing sessions, and route loss, rejection of queued calls, and successful fresh execution with cleared stored state.
GitOrigin-RevId: 914cab3bb45e30a3f3b2afacb5631e42b18e21b0
## Why
Sessions sharing a transport can be admitted to different hosts. Each session needs its own routing token so subsequent RPCs reach the host holding its state.
## What changed
- Capture the optional `x-code-mode-route` metadata from successful `OpenSession` responses and attach it to subsequent session RPCs. Reject tokens longer than 256 bytes and keep new admission attempts free of existing session routes.
- Invalidate a routed session when an `Unavailable` response explicitly sets `x-code-mode-route-lost: true`, allowing a later operation to reopen it without replaying the failed execution. Ordinary `Unavailable` responses preserve the session.
- Allow up to five admission attempts for `Unavailable` and `ResourceExhausted`, with an immediate first retry followed by jittered exponential backoff.
- Order session failure with shutdown so late callback errors cannot cancel an in-flight `CloseSession` RPC.
## Testing
Add regression coverage for independent routing on a shared provider, route-loss recovery without execution replay, preservation of unaffected session state, and callback failures racing shutdown. Extend admission tests to verify the five-attempt limit and recovery tests to distinguish explicit route loss from ordinary unavailability.
GitOrigin-RevId: 5d60ef1afa56beb8c70ba7ab27865128225b0d3d
## Why
A host can reject a request for an unknown session while its lease streams remain open. Keeping that session binding prevents subsequent execution from recovering.
## What changed
Invalidate the session when `Execute` (including its response stream), `Wait`, or `Terminate` returns `NOT_FOUND`, allowing the next execution to open a fresh session. Return the failed call's error without replaying execution.
Document that these RPCs reserve `NOT_FOUND` for unknown sessions, while `CompleteToolCall` can use it for a missing invocation.
## Testing
Add regression coverage for recovery with lease streams still open, no replay of failed execution, and preservation of session state after `INVALID_ARGUMENT`. Add a cancellation-race test confirming that a late tool-completion `NOT_FOUND` leaves the session open.
GitOrigin-RevId: 85b38fdbd6d59268447b6aa6a85ea7c60ec869a7
Jennifer Zhao