fix: handle empty IPC responses

[honor2030]

Summary

• Raise ConnectionError when an IPC peer closes before sending any response, instead of treating EOF as {}.
• Skip malformed/non-dict connection_status replies in browser_connections() so stale endpoints do not crash diagnostics or count as active browsers.
• Add regression coverage for empty EOF and malformed status replies.

Test Plan

• RED: uv run --with pytest python -m pytest tests/unit/test_ipc.py::test_request_raises_connection_error_when_peer_closes_without_response tests/unit/test_admin.py::test_browser_connections_skips_daemon_that_closes_without_response tests/unit/test_admin.py::test_browser_connections_skips_non_dict_connection_status_response -q failed before the fix.
• GREEN: same focused command passed (3 passed).
• GREEN: uv run --with pytest python -m pytest tests -q (97 passed).
• GREEN: uv run python -m compileall src tests.
• GREEN: uv pip check --python .venv/bin/python.
• GREEN: uv run --with pip-audit python -m pip_audit (no known vulnerabilities; local package skipped because it is not on PyPI).
• GREEN: uv run --with ruff python -m ruff check --select B src/browser_harness/_ipc.py src/browser_harness/admin.py tests/unit/test_admin.py tests/unit/test_ipc.py.

Note: repo-wide ruff --select B . currently reports pre-existing B904 findings in src/browser_harness/daemon.py, outside this PR's diff; the changed-file B check passes.

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Summary by cubic

Fixes IPC EOF handling and hardens browser diagnostics to ignore malformed responses. Prevents crashes and stops stale daemons from being counted as active browsers.

• Bug Fixes
  • ipc.request: raise ConnectionError when the peer closes without sending a response (no more {} on EOF).
  • browser_connections(): skip non-dict or "error" connection_status replies so stale endpoints don’t appear active.
  • Added regression tests for empty EOF and malformed status replies.

^{Written for commit 08815e6. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files