`agentcore exec` reports 'No deployed runtimes found' for harness deployments

[jesseturner21]

Summary

agentcore exec reports "No deployed runtimes found" for agents deployed via the harness devenv, even though the deployment is confirmed present through other commands. exec doesn't appear to support harness deployments.

Steps to reproduce

1. Deploy an agent using the harness.
2. Confirm the deployment exists:
   • agentcore status — shows the deployed harness.
   • agentcore invoke --session-id ... — successfully invokes the deployed harness.
3. Run agentcore exec.

Expected behavior

agentcore exec recognizes the harness deployment (consistent with agentcore status and agentcore invoke) and executes against it.

Actual behavior

agentcore exec reports No deployed runtimes found, despite status and invoke both confirming a deployed runtime is present.

Environment

• CLI version: 1.0.0-preview.20
• User agent: AgentCoreCLI/1.0.0-preview.20 (darwin 25.5.0; node/v22.15.0)
• OS: darwin 25.5.0
• Node: v22.15.0