Make projection cycle planning scale-safe

tests/test_projection_contract.py

@@ -14,6 +14,7 @@ from unittest import mock
 
 from docforge.errors import DocForgeError
 from docforge.manual_projection import (
+    _cycles,
     build_manual_projection_package,
     build_manual_render_plan,
 )
@@ -390,6 +391,21 @@ class ProjectionContractTests(unittest.TestCase):
             workflow["cross_references"],
         )
 
+    def test_cycle_detection_handles_the_maximum_deep_graph_iteratively(self) -> None:
+        node_ids = tuple(f"node.{index:05d}" for index in range(10_000))
+        chain = tuple(
+            Edge(node_ids[index], "depends_on", node_ids[index + 1])
+            for index in range(len(node_ids) - 1)
+        )
+        self.assertEqual([], _cycles(node_ids, chain))
+        self.assertEqual(
+            [list(node_ids)],
+            _cycles(
+                node_ids,
+                (*chain, Edge(node_ids[-1], "depends_on", node_ids[0])),
+            ),
+        )
+
     def test_alpha_compatibility_shim_preserves_legacy_identity_and_bytes(self) -> None:
         renderer = GenericHtmlRenderer()
         self.assertEqual(ALPHA_RENDERER_VERSION, renderer.renderer_version)