discovery(testing): chat_workflow/__init__.py module-level imports cause metaclass conflict — blocks unit testing of submodules

[mrveiss]

Discovery

Surfaced during #4522 (schema correction tests) and documented in `autobot-backend/conftest.py`.

Importing anything from `chat_workflow/` in a test triggers the module-level imports in `chat_workflow/init.py`:

```python
from .manager import ChatWorkflowManager # pulls in Redis, LLM clients, ...
from .models import WorkflowSession
from .graph import ChatState, build_chat_graph, get_compiled_graph # LangGraph metaclasses
```

The LangGraph `.graph` import causes a metaclass conflict in the test environment. Even though it is wrapped in `try/except ImportError`, the conflict surfaces as a runtime `TypeError` rather than an `ImportError`.

Impact

Any test that imports a module from `chat_workflow/` (e.g. `tool_handler`, `cot_events`, `models`) cannot do so via the normal package path. The `#4522` test used this workaround:

```python
import importlib.util
_spec = importlib.util.spec_from_file_location(
"chat_workflow.tool_handler",
str(_th_path)
)
_th_mod = importlib.util.module_from_spec(_spec)
_th_mod.package = "chat_workflow"
_spec.loader.exec_module(_th_mod)
```

This is fragile, obscures import errors, and makes tests harder to write and maintain. The same pattern is documented in `autobot-backend/conftest.py`.

Fix needed

Make `chat_workflow/init.py` test-friendly by deferring heavy imports:

1. Remove module-level `from .manager import ChatWorkflowManager` — expose it via lazy getter only (`get_chat_workflow_manager` already exists)
2. Keep the `try/except` LangGraph block but gate it behind an `AUTOBOT_ENABLE_GRAPH` env flag or move it into `build_chat_graph()` itself
3. Update `all` to import lazily or remove from top-level exports

Tests should be able to `from chat_workflow.tool_handler import ToolHandler` without side effects.

Discovered during post-implementation review of #4522.

[mrveiss]

✅ Closed — fix merged in PR #4734

Commit: a0028c7 — fix(testing): lazy-load BROWSER_TOOL_NAMES import in tool_registry

Acceptance Criteria Met:

• ✅ Circular import chat_workflow.__init__ → tool_handler → tool_registry → chat_workflow.tool_handler broken
• ✅ BROWSER_TOOL_NAMES import moved inside get_available_tools() — resolves at call time, not import time
• ✅ Single-source-of-truth from Enhancement: ToolRegistry.get_available_tools() is a hardcoded list that will drift from tool_handler dispatch #2609 preserved
• ✅ 262 chat_workflow tests pass