Add disabled GPS momentum penalty prototype

docs/compaction-handoff.md

@@ -2,6 +2,40 @@
 
 Current date/time context: 2026-06-27, local timezone America/Chicago.
 
+## 2026-06-27 Disabled Momentum Penalty Prototype
+
+- Static disassembly of the full async solver relaxation cluster is updated.
+  `0x40ba58` has exactly four direct callers:
+  `0x40b175`, `0x40b4ac`, `0x40b6d5`, and `0x40bca7`.
+- The ordinary adjacency walkers are still the clean first patch surface:
+  `0x40b304` reaches relax at `0x40b4ac`, and `0x40b540` reaches relax at
+  `0x40b6d5`. Both compute vanilla tentative `g` in `xmm6`, copy it to
+  `xmm3`, write `f = g + h` at `[rsp+0x20]`, and then call `0x40ba58`.
+- Patch starts are `0x40b49a` for list A and `0x40b6c3` for list B. Each
+  replaces 23 bytes ending at the vanilla `0x40ba58` call and jumps to a
+  private executable cave. The cave reproduces the overwritten vanilla math,
+  adds a fixed nonnegative cost to `xmm6`, recomputes `f` from the penalized
+  `g`, calls vanilla `0x40ba58`, and jumps back after the overwritten block.
+- Added a disabled-by-default RED4ext prototype in
+  `red4ext/EdgeWeightGPS/src/Main.cpp`:
+  `kEnableGpsMomentumPenaltyInlinePatch = false`,
+  `kGpsMomentumFixedEdgePenalty = 8.0f`.
+- This first prototype is only a short-segment/churn lever. It adds a fixed
+  per-edge penalty on ordinary neighbor expansion, so routes that stair-step
+  through many small pieces become more expensive without making highways
+  cheaper. It does not yet compute turn angle, ramp transition cost, or
+  predecessor/current/neighbor geometry.
+- The first prototype intentionally leaves the two non-ordinary relax paths
+  vanilla:
+  `0x40b175` appears to be a target/terminal candidate path, and `0x40bca7`
+  appears to be a special continuation/end-candidate path from `0x40bbbc`.
+  Patch them only after the ordinary expansion test proves stable.
+- Build verification passed in toolbox:
+  `toolbox run -c 2077 ./tools/build_red4ext_shim.sh`.
+- The prototype was not installed into the live game directory. To test later,
+  flip `kEnableGpsMomentumPenaltyInlinePatch` to `true`, rebuild, install only
+  after the game is cold, and compare against the fixed El Coyote route set.
+
 ## 2026-06-27 Routing Literature And Engine Research
 
 - Added `docs/gps-routing-research.md` as the durable summary of the GPS