test(agents): session-transport-macos flakes with ENOTEMPTY in gentle-agents teardown #1840

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Problem

The session-transport-macos CI job fails intermittently with ENOTEMPTY while a tests/gentle-agents.test.ts case removes its temporary profile directory. It has failed on at least two PRs (#1832 and #1835) in different tests and passed on rerun both times, so it blocks merges for no product reason.

Root cause: session_shutdown persists finished subagent history asynchronously (persist() calls void saveTask(...) into the profile's tasks directory). The test then calls rmSync(profile, { recursive: true, force: true }) right after shutdown. On macOS the late history write can land between the recursive deletion of the children and the removal of the directory, so rmdir sees a non-empty directory.

Steps to reproduce

1. Run the session-transport-macos job (or node --experimental-strip-types --test tests/gentle-agents.test.ts on macOS) repeatedly.
2. Observe an occasional failure in a teardown rmSync of a gentle-agents-continue-* or similar temporary directory.

Expected and actual behavior

Expected: test teardown removes its temporary directories reliably.
Actual: Error: ENOTEMPTY, Directory not empty: <tmp>/gentle-agents-continue-XXXX in "a writer continuation without its own section inherits the admitted surfaces end to end" (PR #1835) and in "a subdirectory session cwd and workspace_root ... share one writer key" (PR #1832).

gentle-pi version

main at aa2c038 (package 4.0.0)

Pi version

1.0.0 (development dependency)

Operating system

macOS

Relevant logs or error output (optional)

✖ a writer continuation without its own section inherits the admitted surfaces end to end (55.832875ms)
  Error: ENOTEMPTY, Directory not empty: <tmp>/gentle-agents-continue-ZJrSQZ
    code: 'ENOTEMPTY',