fix: resolve_text follows a node shared by two branches

The cycle guard used one visited set for the whole walk, so a string node
read twice (a diamond, or StringConcatenate with the same source on both
inputs) made the second branch None and the prompt text unknowable. Cycle
detection is now scoped to the current path; a separate visit counter
keeps MAX_VISITS as the bound on total work.

tests/test_prompt_graph.py

@@ -361,6 +361,64 @@ class TestResolveText(unittest.TestCase):
                 resolve_text(self._linked(source), "1"), source["class_type"]
             )
 
+    def test_same_source_used_twice_resolves_both_branches(self):
+        # StringConcatenate(string_a=X, string_b=X): X is not a cycle, it is
+        # simply shared, and must resolve in both branches.
+        graph = {
+            "1": pm(["2", 0]),
+            "2": {
+                "class_type": "StringConcatenate",
+                "inputs": {
+                    "string_a": ["3", 0],
+                    "string_b": ["3", 0],
+                    "delimiter": "+",
+                },
+            },
+            "3": {"class_type": "PrimitiveString", "inputs": {"value": "x"}},
+        }
+        self.assertEqual(resolve_text(graph, "1"), "x+x")
+
+    def test_diamond_graph_resolves(self):
+        # 1 <- 2 <- (3, 4) and both 3 and 4 read from 5
+        graph = {
+            "1": pm(["2", 0]),
+            "2": {
+                "class_type": "StringConcatenate",
+                "inputs": {
+                    "string_a": ["3", 0],
+                    "string_b": ["4", 0],
+                    "delimiter": " ",
+                },
+            },
+            "3": {"class_type": "ShowText|pysssss", "inputs": {"text": ["5", 0]}},
+            "4": {"class_type": "Text Multiline", "inputs": {"text": ["5", 0]}},
+            "5": {"class_type": "PrimitiveString", "inputs": {"value": "cat"}},
+        }
+        self.assertEqual(resolve_text(graph, "1"), "cat cat")
+
+    def test_indirect_cycle_returns_none(self):
+        graph = {
+            "1": pm(["2", 0]),
+            "2": {"class_type": "ShowText|pysssss", "inputs": {"text": ["3", 0]}},
+            "3": {"class_type": "Text Multiline", "inputs": {"text": ["2", 0]}},
+        }
+        self.assertIsNone(resolve_text(graph, "1"))
+
+    def test_visit_budget_bounds_shared_fan_out(self):
+        # A chain of concatenations that each read the previous node twice
+        # expands exponentially without memoisation; MAX_VISITS must cap it.
+        graph = {"0": {"class_type": "PrimitiveString", "inputs": {"value": "a"}}}
+        for i in range(1, 400):
+            prev = [str(i - 1), 0]
+            graph[str(i)] = {
+                "class_type": "StringConcatenate",
+                "inputs": {"string_a": prev, "string_b": prev, "delimiter": ""},
+            }
+        graph["pm"] = pm(["399", 0])
+        start = time.monotonic()
+        self.assertIsNone(resolve_text(graph, "pm"))
+        self.assertLess(time.monotonic() - start, 2.0)
+
     def test_cycles_and_missing_links(self):
         graph = {
             "1": pm(["2", 0]),

utils/prompt_graph.py

@@ -181,24 +181,33 @@ def resolve_text(graph: Any, node_id: str) -> Optional[str]:
     """
     if not isinstance(graph, dict):
         return None
-    seen = set()
+    # Cycle detection is scoped to the current path so a node read by two
+    # branches (a diamond, or StringConcatenate(string_a=X, string_b=X))
+    # resolves in both; the visit counter bounds total work regardless.
+    path = {str(node_id)}
+    visits = [0]
 
     def resolve(value: Any) -> Optional[str]:
         if isinstance(value, str):
             return value
-        if not _is_link(value) or len(seen) >= MAX_VISITS:
+        if not _is_link(value):
+            return None
+        visits[0] += 1
+        if visits[0] > MAX_VISITS:
             return None
         source_id = str(value[0])
-        if source_id in seen:
+        if source_id in path:
             return None
-        seen.add(source_id)
         source = graph.get(source_id)
         if not isinstance(source, dict):
             return None
-        return _resolve_string_node(
-            str(source.get("class_type", "")), _inputs(source), resolve
-        )
+        path.add(source_id)
+        try:
+            return _resolve_string_node(
+                str(source.get("class_type", "")), _inputs(source), resolve
+            )
+        finally:
+            path.discard(source_id)
 
-    seen.add(str(node_id))
     text = resolve(_inputs(graph.get(str(node_id))).get("text"))
     return text.strip() if isinstance(text, str) and text.strip() else None