docs(styleguide): add python.md §17 (Banned Patterns — LLM Default Anti-Patterns)

conductor/code_styleguides/python.md

@@ -213,7 +213,127 @@ To prevent "God Object" bloat in core controllers (like `AppController`):
 - **Handler Maps:** Replace massive `if/elif` blocks (like those in event dispatchers) with dictionaries mapping keys to module-level handler functions.
 - **Inner Class Extraction:** Never define nested classes or functions within methods. Move them to the module level.
 
-## 16. See Also — Per-File Pattern Demonstrations
+## 17. Banned Patterns (LLM Default Anti-Patterns) (Added 2026-06-25)
+
+**C11/Odin/Jai semantics in a Python runtime.** This codebase is written in Python because of practical constraints, but the convention is to make Python behave as close to a statically-typed value-typed language as the runtime allows. LLMs default to the following patterns because that's what idiomatic Python training data looks like. **All of these are BANNED in non-boundary code.** See `data_oriented_design.md` §8.5 for the canonical mandate.
+
+### 17.1 Banned: `dict[str, Any]`
+
+```python
+# BANNED:
+def process(event: dict[str, Any]) -> None:
+ if event.get("kind") == "tool_call":
+
+# BANNED:
+flat: dict[str, Any] = project_manager.flat_config(...)
+
+# CORRECT:
+def process(event: CommsLogEntry) -> None:
+ if event.kind == "tool_call":
+
+# CORRECT (boundary only):
+def _parse_wire(raw: str) -> Metadata:
+ return Metadata.from_dict(tomllib.loads(raw))
+```
+
+### 17.2 Banned: `Any`
+
+```python
+# BANNED:
+def _to_typed_tool_call(tc: Any) -> ToolCall:
+ return ToolCall(id=getattr(tc, "id", "") or "", ...)
+
+# CORRECT:
+def _parse_wire_tool_call(wire: dict[str, Any]) -> ToolCall:
+ """Boundary: parse MCP wire dict to typed ToolCall."""
+ return ToolCall.from_dict(wire)
+```
+
+### 17.3 Banned: `Optional[T]` returns
+
+```python
+# BANNED:
+def find_ticket(self, id: str) -> Optional[Ticket]:
+ for t in self.active_tickets:
+  if t.id == id: return t
+ return None   # ← silent failure; consumer has to None-check
+
+# CORRECT (Result pattern):
+def find_ticket(self, id: str) -> Result[Ticket]:
+ for t in self.active_tickets:
+  if t.id == id: return Result(data=t)
+ return Result(data=NIL_TICKET, errors=[ErrorInfo(...)])  # drain point handles
+
+# CORRECT (NIL_T sentinel — preferred when consumer just reads fields):
+def find_ticket(self, id: str) -> Ticket:
+ for t in self.active_tickets:
+  if t.id == id: return t
+ return NIL_TICKET   # zero-initialized frozen dataclass; safe to read fields
+```
+
+### 17.4 Banned: `hasattr()` for entity type dispatch
+
+```python
+# BANNED:
+def handle_event(self, event: Metadata) -> None:
+ if hasattr(event, 'tool_calls'):
+  # tool call path
+ elif hasattr(event, 'source_tier'):
+  # mma path
+ elif hasattr(event, 'path'):
+  # file path
+
+# CORRECT (typed Union dispatch):
+def handle_event(self, event: CommsLogEntry | FileItem | HistoryMessage) -> None:
+ if isinstance(event, CommsLogEntry):
+  # mma path
+ elif isinstance(event, FileItem):
+  # file path
+ elif isinstance(event, HistoryMessage):
+  # tool call path
+
+# CORRECT (preferred — refactor so no dispatch is needed):
+def _handle_comms_entry(self, event: CommsLogEntry) -> None: ...
+def _handle_file_item(self, event: FileItem) -> None: ...
+def _handle_history(self, event: HistoryMessage) -> None: ...
+```
+
+### 17.5 Banned: `getattr(x, 'field', default)` for type dispatch
+
+```python
+# BANNED:
+tool_id = getattr(tc, "id", "") or ""
+tool_name = getattr(tc.function, "name", "") or ""
+
+# CORRECT:
+tool_id = tc.id
+tool_name = tc.function.name
+```
+
+### 17.6 Banned: `.get('field', default)` on a `dict[str, Any]`
+
+```python
+# BANNED:
+tier = entry.get('source_tier', 'main')
+model = entry.get('model', 'unknown')
+
+# CORRECT (direct attribute access on the typed dataclass):
+tier = entry.source_tier
+model = entry.model
+```
+
+### 17.7 The one exception: the boundary layer
+
+The ONLY place these patterns are allowed is at the literal wire boundary — the function that calls `tomllib.load()`, `json.loads()`, or a vendor SDK's response parser. The boundary is 2-3 functions per file. Every consumer IMMEDIATELY converts to a typed dataclass via `from_dict()`.
+
+### 17.8 Enforcement
+
+- `scripts/audit_weak_types.py --strict` — flags `dict[str, Any]`, `Any`, anonymous tuple returns
+- `scripts/audit_optional_in_3_files.py --strict` — flags `Optional[T]` in the 3 refactored files (extended to ALL `src/*.py` per the c11_python track)
+- The new `boundary_layer` audit (planned in `conductor/tracks/cruft_elimination_20260627/spec.md`) — documents every `Metadata` usage with justification
+- Pre-commit: every commit MUST pass all three audits above
+
+## 18. See Also — Per-File Pattern Demonstrations
 
 The following per-source-file guides show these conventions applied in real code: