[huxiaoyi-ovo]

Summary

Greedy Best-First Search currently mishandles two outcomes in planning():

1. Unreachable goal: when open_set is exhausted, the method still calls path reconstruction. It inserts the last expanded node under the goal's unset parent index (-1), returning a fabricated path that includes the unreachable goal.
2. Reached goal: the reconstruction setup injects the reached goal node into its parent's closed_set entry, then adds that goal node a second time to the returned coordinates.

Fix

• Return ([], []) when the search frontier is empty.
• On success, reconstruct the path directly from the reached node via its existing parent pointers.
• Preserve the existing goal-to-start path ordering, planning interface, obstacle checks, and search strategy.

Regression tests

• A bounded grid split by a full wall returns an empty path for an unreachable goal.
• An adjacent reachable goal returns [(2, 2), (1, 2)] exactly, without repeating the goal.
• A coincident start and goal returns a single waypoint.

Changes are limited to the Greedy Best-First planner and its test file. No new dependencies.

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AI disclosure: ChatGPT assisted with source analysis, implementation, and regression tests.