Merge upstream 5e645791ac.
Retain the PM feature-flag owner and add upstream connection options.
Use the deny-only window-open policy while trusted external links keep
the existing IPC path. Keep both session-import and external-link copy.
Preserve captured timeout output when adding terminal yield handoff.
Quickstart tests patch the explicit upstream model-assignment owner.
Migrate incoming legacy OS markers to the branch's platforms gate.
Desktop renderer and Electron typechecks passed. Targeted Electron tests
passed (42 tests), Python conflict checks passed (26 tests, 3 skips),
and the plugin-compat import checker passed. CI owns the broad merge gate.
ce49cdbc59