Fix GraphFlow cycle detection to properly clean up recursion state

[Copilot]

The has_cycles_with_exit() method in GraphFlow had a bug where the DFS algorithm would return True immediately upon finding a cycle with valid exit conditions, without properly cleaning up the recursion state (rec_stack and path). This left stale data that could cause incorrect behavior when processing subsequent unvisited nodes in graphs with multiple components.

Problem

Consider a graph structure like this:

graph = DiGraph(
    nodes={
        "A": DiGraphNode(name="A", edges=[
            DiGraphEdge(target="B"),
            DiGraphEdge(target="D")  # This branch could be affected
        ]),
        "B": DiGraphNode(name="B", edges=[DiGraphEdge(target="C")]),
        "C": DiGraphNode(name="C", edges=[DiGraphEdge(target="A", condition="loop")]),  # Valid cycle
        "D": DiGraphNode(name="D", edges=[]),
        "E": DiGraphNode(name="E", edges=[])  # Disconnected component
    }
)

When the DFS processes the cycle A → B → C → A, it would find the valid exit condition and return True immediately. However, this skipped the cleanup code (rec_stack.remove(node_name) and path.pop()), leaving nodes A, B, and C in the recursion stack. When processing the disconnected component E later, this stale state could cause incorrect behavior.

Solution

Changed the DFS algorithm to use a local cycle variable to accumulate results instead of returning immediately:

Before (buggy):

def dfs(node_name: str) -> bool:
    # ... setup code ...
    for edge in self.nodes[node_name].edges:
        if target not in visited:
            if dfs(target):
                return True  # Early return without cleanup
        elif target in rec_stack:
            # ... cycle validation ...
            return True  # Early return without cleanup
    
    rec_stack.remove(node_name)  # Only reached if no cycles found
    path.pop()
    return False

After (fixed):

def dfs(node_name: str) -> bool:
    # ... setup code ...
    cycle = False  # Track cycle detection locally
    for edge in self.nodes[node_name].edges:
        if target not in visited:
            if dfs(target):
                cycle = True  # Continue processing instead of early return
        elif target in rec_stack:
            # ... cycle validation ...
            cycle = True  # Continue processing instead of early return
    
    rec_stack.remove(node_name)  # Always executed
    path.pop()
    return cycle  # Return accumulated result

Testing

Added test_cycle_detection_cleanup_bug() to the test suite to prevent regression of this issue. All existing cycle detection tests continue to pass, ensuring no regressions were introduced.

Fixes #6985.

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.93%. Comparing base (79d5d6a) to head (c4dc252).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7026   +/-   ##
=======================================
  Coverage   80.93%   80.93%           
=======================================
  Files         237      237           
  Lines       18240    18241    +1     
=======================================
+ Hits        14762    14763    +1     
  Misses       3478     3478           

Flag	Coverage Δ
unittests	80.93% <100.00%> (+<0.01%)	⬆️

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