External Agent slash commands cannot wake suspended sessions

Observed behavior

When an external Agent's Run (or the underlying agent session) is suspended/paused, slash commands such as model selection cannot be used to wake or resume it. Invoking a slash command while the Agent is suspended does not proceed.

The user must first send a normal conversational message to the Agent. That interaction resumes the underlying session; only after that can slash commands such as selecting a model be used successfully.

Reproduction

1. Start or open an external Agent.
2. Leave it in a suspended/paused state, including when the underlying session is suspended.
3. Invoke a slash command, such as model selection.
4. Observe that the command cannot wake/resume the Agent or complete.
5. Send a normal conversational message first.
6. After the session resumes, invoke the same slash command; it works.

Open question

Please determine whether this is intentional lifecycle behavior (slash commands require an active Agent turn/session by design) or a bug. If it is a bug, slash commands that are valid session-level operations should be able to resume or target a suspended external Agent, or should provide a clear state-specific explanation and recovery path.

Investigation directions

• Trace slash-command dispatch and the normal-message dispatch paths for suspended external Agents.
• Compare how each path acquires/resumes the underlying Agent session and turn lease.
• Check whether model selection and similar commands are incorrectly gated on an already-active turn.
• Define expected behavior for suspended, idle, and terminated sessions, including an explicit user-facing error if wake-up is intentionally unsupported.

Trace the slash-command dispatch and normal-message dispatch paths for suspended external Agents, then compare how each acquires or resumes the underlying session and turn lease. Check model selection and similar commands for active-turn gating. Done means the intended behavior is defined for suspended, idle, and terminated sessions, with commands either resuming valid sessions or providing a clear recovery error.