[barrybecker4]

Tantrix and the new bb4-optimization hooks: tried, mixed result, so off by default

Draft, for you to decide. Depends on bb4-optimization #34 (merged). Independent of the Red PR (#66).

What it adds

• TantrixPath supports moves. A Tantrix neighbor is a whole rearranged path (a pivot reversal or swap of sub paths), not a swap, so a move (PathMove) just carries the path it leads to. applyMove(proposeMove(r)) is the same path as getRandomNeighbor(r) (tested).
• GuidedPivot: pick a tile whose secondary colors don't match its neighbors, and rearrange the path only at that tile and the ones beside it, choosing among the alternatives the same way a random neighbor does. Offered through TantrixPath.proposeGuidedMove and GeneticSearchSolver.proposeGuidedMove.
• GeneticSearchSolver.GUIDED_MOVE_PROBABILITY feeds the tuned simulated annealing's guidedMoveProbability. It is 0.0, so behavior is unchanged.

Measurements (this machine, 20 s cap, runs that found a solution)

Simulated annealing (the tuned one), 40 runs each:

Tiles	Guided probability	Solved	Median time
9	0	37/40	42 ms
9	0.5	40/40	104 ms
9	1.0	40/40	134 ms
12	0	35/40	70 ms
12	0.5	40/40	616 ms
12	1.0	38/40	605 ms

Genetic search, 10 runs on 9 tiles: 7, 6, 5 solved with probability 0, 0.5, 1.0 (no gain). Global simulated annealing solved 10/10 at every setting.

So annealing becomes more reliable but each solved run takes 2 to 9 times longer, because a guided neighbor builds and scores several rearrangements. Genetic search does not benefit. That is not the clear win Red got, so I left it off. The exact solvers (SHAPE_THEN_ASSIGN and friends) solve these in 20 to 35 ms anyway.

Choices for you

• Merge as is: the hook is there and tested, one constant turns it on.
• Set the constant to 0.5 if you would rather have fewer failed annealing runs than a fast typical run.
• Close it if you don't want the extra code.

Testing

Manual build: GuidedPivotSuite (9 tests) passes; the only failures are the same two Tantrix suites as before (PathPivotPermuterSuite, SubPathMutatorBase load). I could not run Gradle here.

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