Fix OMP presence after subagent shutdown

[panosAthDBX]

Closes #669

Summary

• keep OMP process presence alive when an in-process task subagent shuts down
• map OMP session_shutdown to idle instead of session_end, leaving final cleanup to PID liveness and surface closure
• add regression coverage that rejects session_end from the bundled OMP extension

OMP loads configured extensions into each in-process subagent session. Those sessions share the top-level OMP process PID and Supacode surface, so a subagent session_shutdown previously removed the main process presence record.

Type of change

• Bug fix (the linked issue is a bug report)
• Feature (the linked issue is a feature request marked ready)
• Documentation
• Other (please describe)

How was this tested?

• make check passes (format + lint)
• make test passes
• I built and ran the app to confirm the change works

make build-app passes. The focused OmpSettingsInstallerTests invocation was attempted twice, but the test target currently fails during dependency compilation before tests execute because TCA's WritableKeyPath does not conform to Sendable under the installed toolchain.

The locally installed OMP extension was also updated with the same mapping for new OMP sessions.

AI tool disclosure (optional)

• Model(s): OpenAI GPT-5.6 Sol
• Harness / tools: Oh My Pi

Checklist

• This pull request is linked to an issue with Closes # above.
• For a feature, the linked issue is labeled ready.
• I am the author of this work and accountable for it; no commit is authored or co-authored by an AI agent.
• I have read the Contributing guide and the Code of Conduct.

[sbertix]

I trust you with this one (can't test it) 💪 thanks 🙇‍♂️