Add per-session code-mode execution limits (#37114)

## What changed

- Add `create_session_with_limits` and session-scoped cell execution limits.
- Clamp execute and wait yield times to the session's `max_yield_time_ms`
  without terminating the running cell.
- Negotiate support with remote code-mode hosts and include non-default limits
  in `session/open`, while keeping unlimited sessions compatible with hosts and
  providers that do not support limits.

## Testing

- Cover yield-time clamping, zero-timeout behavior, and isolation between
  sessions.
- Cover wire serialization, capability negotiation, unsupported hosts, and
  shared process-host execution.

GitOrigin-RevId: 9517321cd605bb87f93eeaa6ba331cc2e346e582

codex-rs/code-mode-protocol/src/host/message.rs

@@ -17,6 +17,7 @@ use super::WireCellId;
 use super::WireExecuteRequest;
 use super::WireNestedToolCall;
 use super::WireRuntimeResponse;
+use super::WireSessionCellExecutionLimits;
 use super::WireWaitOutcome;
 use super::WireWaitRequest;
 
@@ -242,7 +243,11 @@ impl HostToClient {
 #[serde(deny_unknown_fields, tag = "method", rename_all_fields = "camelCase")]
 pub enum HostRequest {
     #[serde(rename = "session/open")]
-    OpenSession { session_id: SessionId },
+    OpenSession {
+        session_id: SessionId,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        cell_execution_limits: Option<WireSessionCellExecutionLimits>,
+    },
     #[serde(rename = "session/execute")]
     Execute {
         session_id: SessionId,