feat(audit): add FunctionRef dataclass (frozen, 4 fields)

fqname, file, line, role. Used in ProducerConsumerGraph edges
and per-aggregate producer/consumer lists. Per error_handling.md
Pattern 1 (immutability for cross-thread safety).
2 unit tests passing.

src/code_path_audit.py

@@ -9,6 +9,7 @@ postfix DSL + markdown + prefix tree text. See
 conductor/tracks/code_path_audit_20260607/spec_v2.md.
 """
 from __future__ import annotations
+from dataclasses import dataclass
 from typing import Literal
 
 AggregateKind = Literal[
@@ -52,3 +53,10 @@ RecommendedDirection = Literal[
  "hold",
  "insufficient_data",
 ]
+
+@dataclass(frozen=True)
+class FunctionRef:
+ fqname: str
+ file: str
+ line: int
+ role: str

tests/test_code_path_audit.py

@@ -1,10 +1,13 @@
 """Tests for src.code_path_audit v2 - Phase 1 (data model)."""
+from __future__ import annotations
+import pytest
 from src.code_path_audit import (
  AggregateKind,
  MemoryDim,
  AccessPattern,
  Frequency,
  RecommendedDirection,
+ FunctionRef,
 )
 
 def test_aggregate_kind_4_values() -> None:
@@ -31,3 +34,28 @@ def test_recommended_direction_4_values() -> None:
  """RecommendedDirection is a Literal with 4 values: componentize, unify, hold, insufficient_data."""
  expected = {"componentize", "unify", "hold", "insufficient_data"}
  assert set(RecommendedDirection.__args__) == expected
+
+def test_function_ref_4_fields() -> None:
+ """FunctionRef has fqname, file, line, role (per spec)."""
+ ref = FunctionRef(
+ fqname="src.ai_client.AIClient.send_result",
+ file="src/ai_client.py",
+ line=100,
+ role="producer",
+ )
+ assert ref.fqname == "src.ai_client.AIClient.send_result"
+ assert ref.file == "src/ai_client.py"
+ assert ref.line == 100
+ assert ref.role == "producer"
+
+def test_function_ref_frozen() -> None:
+ """FunctionRef is frozen (immutability per error_handling.md)."""
+ ref = FunctionRef(
+ fqname="src.x.y",
+ file="src/x.py",
+ line=1,
+ role="consumer",
+ )
+ with pytest.raises((AttributeError, Exception)) as exc_info:
+  ref.fqname = "src.z.w"
+ assert "frozen" in str(exc_info.value).lower() or "cannot assign" in str(exc_info.value).lower()