Make dependency validation linear

tests/test_core.py

@@ -8,7 +8,10 @@ import sqlite3
 import sys
 import tempfile
 import unittest
+from collections.abc import Iterator
+from dataclasses import replace
 from pathlib import Path
+from typing import TypeVar, cast
 from unittest import mock
 
 ROOT = Path(__file__).resolve().parents[1]
@@ -18,9 +21,26 @@ from docforge.cli import main  # noqa: E402
 from docforge.context import compile_context  # noqa: E402
 from docforge.errors import DocForgeError  # noqa: E402
 from docforge.index import ProjectIndex  # noqa: E402
-from docforge.project import Project  # noqa: E402
+from docforge.models import Edge  # noqa: E402
+from docforge.project import Project, validate_graph  # noqa: E402
 
 FIXTURES = ROOT / "tests" / "fixtures"
+T = TypeVar("T")
+
+
+class CountingTuple(tuple[T, ...]):
+    """Count complete iteration passes without changing tuple behavior."""
+
+    iterations: int
+
+    def __new__(cls, values: tuple[T, ...]) -> CountingTuple[T]:
+        instance = super().__new__(cls, values)
+        instance.iterations = 0
+        return instance
+
+    def __iter__(self) -> Iterator[T]:
+        self.iterations += 1
+        return super().__iter__()
 
 
 class DocForgeCoreTests(unittest.TestCase):
@@ -149,6 +169,31 @@ class DocForgeCoreTests(unittest.TestCase):
             with self.assertRaisesRegex(DocForgeError, "cycle"):
                 Project.open(root).load()
 
+    def test_graph_validation_uses_a_bounded_number_of_edge_passes(self) -> None:
+        snapshot = Project.open(FIXTURES / "alpha").load()
+        nodes = tuple(
+            replace(
+                snapshot.nodes[0],
+                node_id=f"linear.node-{index:05d}",
+                source_path=f"docs/node-{index:05d}.md",
+            )
+            for index in range(2_000)
+        )
+        edges = CountingTuple(
+            tuple(
+                Edge(
+                    f"linear.node-{index:05d}",
+                    "depends_on",
+                    f"linear.node-{index - 1:05d}",
+                )
+                for index in range(1, len(nodes))
+            )
+        )
+
+        validate_graph(nodes, cast(tuple[Edge, ...], edges))
+
+        self.assertLessEqual(edges.iterations, 4)
+
     def test_index_build_is_repeatable_and_validates_every_row(self) -> None:
         with tempfile.TemporaryDirectory() as directory:
             root = self.copy_fixture("alpha", Path(directory))