fix(cliffs): port fixImpossibleCells' self-retry (#18)

[wormeyman]

The last surviving candidate from #77, decompiled whole. It turned up a real unported behaviour - and, honestly, one that does not move #18.

The bool is a retry flag the function sets on itself

CellEdgeCliffCrossingArray::fixImpossibleCells(bool) at 0x10160c550. On reaching a cell it cannot fix, the tail does:

uVar10 = param_2 & 1;  param_2 = 1;
if (uVar10 != 0) { log("Unable to remove excess cliff cell edge crossings"); return; }
goto <top of function>;

It turns the flag on and restarts the entire pass, which now begins by zeroing the eight outer edges of the chunk's four corner cells. A second failure abandons the rest of the chunk. The restart re-sweeps the arrays as already mutated by the abandoned pass, not the raw crossings.

cliffs-NOTES.md said this step "never runs in this path at all", reasoning from crossingsForChunk passing false. That is the general error worth naming: a parameter's value at the call site says what the caller wants, not what the function does with it.

Everything else in the sweep already matched - L, T, R, B order, the same boundary guards, the same legality set. The engine counts non-zero edges and consults the orientation table only when the count is below 3; that is pure optimisation, since all 20 placing codes have one or two crossings.

It does not fix #18, and the numbers say so

	before	after
[0,0] placed	335	335
[1500,1500] placed	1065	1065
[-1200,800] placed	375	375
recall / precision / orientation count	—	all identical

The retry fires once in 512 chunks over the committed captures - one chunk of Vulcanus [1500,1500], zero across both Nauvis seeds and the other two Vulcanus regions - and changes not one placed cell. This is correctness, not progress.

So it needs its own test

Because the integration fixtures barely execute the branch, test/fixImpossibleCellsRetry.spec.ts constructs a stuck corner directly: L = +1, T = -1 at cell (0,0) is code 0x4C, illegal, with both crossings on edges the sweep is forbidden to clear. Disabling the retry fails 3 of its 5 tests. The other two are the setup assertion (proving the constructed cell really is stuck and illegal) and a control that the corner step does not fire on a healthy chunk - it clears eight edges unconditionally, so firing spuriously would delete real cliffs.

Where #18 stands now

Everything upstream is eliminated and the rule is now read end to end - generateCliffs, tryToAddCliff, crossingsForChunk, fixImpossibleCells. 12.5% of shared cells still carry the wrong crossings (29.8% at [0,0]), with 125 of 175 differing in exactly two edges. I do not have a next candidate from the disassembly; the code as read matches the port.

pnpm run verify green: 305 files checked, 1284 tests.

🤖 Generated with Claude Code

https://claude.ai/code/session_013eczw9uoWDfN6Wc6kA7UBY