[trissim]

Fixes the main red that #2771 (23becf5) introduced: tests/test_native_input_bus_path.py::test_saved_owner_dm_replies... raised RelationViolationError: Copied bus ... cannot write external session inside the installer's nested run.

Cause. ExternalSessionLocation.writable compared the root with CommsRoute.current(), which is the machine-wide published route. A private root is never that route, so it refused to write a harness transcript it had published itself.

Fix. The decision now comes from the session's own declared location.

• ExternalSessionLocation declares published, the root whose registry published it. The wire form is {"path", "published"}.
• Only the root named in published may write the file. A copy keeps that root, so the copy reads the file and refuses to write it.
• RegistrySessionLocation.publish(absolute, root, publisher) is the single place that picks the class. A path under the root becomes Bus. Anything else becomes External, owned by the publishing root.
• Rebinding a bus transcript to another root yields an External location owned by the source root.
• session_file.py no longer imports CommsRoute.

Proof.

• tests/test_carry_session_locations.py (including a new private-root write test) and tests/test_native_input_bus_path.py: 6 passed.
• The session suites touched by the location type: 129 passed, 4 failed. All 4 also fail on main 278750a:
  • test_check_root x2: "A check root belongs under the caller's agent-scratch directory";
  • test_start::test_real_stopped_owner...;
  • test_native_owner_launcher_resolution::test_fork_runs....
• ruff: session_file.py has 0 findings (main has 0); the carry test has 5 (main has 5). The black diff and the mypy count for session_file.py are the same as main's.

🤖 Generated with Claude Code

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

An organization owner can choose the repository organization as the billing source for reviews requested by members with a paid Copilot license. Learn about Copilot code review billing.