The single-agent-era filesystem middleware (app/agents/shared/middleware/
filesystem.py, ~2000 lines) was never instantiated in production, yet three
unit suites validated it — an illusory guardrail while the live decomposed
middleware (multi_agent_chat/middleware/shared/filesystem) was unguarded.
Close the gap before reorganizing the agents module:
- Add 14 integration tests driving live B's tools in desktop mode (real
on-disk effects) and cloud mode (in-state staging, namespace policy).
- Port all high-value dead-twin assertions onto the live path: cloud rm/rmdir
staging + guard rails, KBPostgresBackend delete-view filter, mode-scoped
system prompt, cwd/relative/namespace resolution, multi-root mount
normalization.
- Delete dead twin filesystem.py, drop its __init__ re-export, and retire its
3 dead-twin tests.
Verified: test_import_all + middleware unit + FS integration all green.
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