feat: add project adapter shadow contract

src/docforge/project.py

@@ -11,7 +11,14 @@ from dataclasses import replace
 from pathlib import Path
 from typing import Any
 
-from .config_validation import ID_PATTERN, confined_path, positive_int, require_string, string_list
+from .config_validation import (
+    AUTHORITIES,
+    ID_PATTERN,
+    confined_path,
+    positive_int,
+    require_string,
+    string_list,
+)
 from .errors import DocForgeError
 from .models import (
     ContextProfile,
@@ -24,7 +31,6 @@ from .models import (
 )
 from .render_config import load_render_config
 
-_AUTHORITIES = frozenset({"authoritative", "approved_plan", "derived", "proposal", "historical"})
 _CORE_METADATA = frozenset(
     {
         "schema_version",
@@ -363,7 +369,7 @@ def validated_node_from_record(
     if ID_PATTERN.fullmatch(node_id) is None:
         raise DocForgeError("invalid_source", f"{source.name}: node ID is invalid", id=node_id)
     authority = require_string(record, "authority", source)
-    if authority not in _AUTHORITIES:
+    if authority not in AUTHORITIES:
         raise DocForgeError(
             "invalid_source", f"{source.name}: authority is invalid", authority=authority
         )