Add live-tunable GPS solver highway weight

docs/compaction-handoff.md

@@ -2,6 +2,41 @@
 
 Current date/time context: 2026-06-26, local timezone America/Chicago.
 
+## 2026-06-26 Confirmed Solver-Cost Patch
+
+- We have unequivocally found the player GPS route-cost lever.
+- The crashing RED4ext detour on `0x40bb40` has been replaced by an inline
+  patch at the road-tail block `0x40bb98`. The patch preserves vanilla
+  `node+0x93` behavior, checks `node+0x88 & 0x4000` for `Highway`, and then
+  multiplies highway lane cost by a tunable float.
+- This inline patch avoids the register-clobber crash from the C++ detour.
+  Static disassembly showed the optimized caller reusing volatile state after
+  calling the tiny vanilla multiplier helper.
+- The proof build used highway multiplier `0.35` and visibly changed player
+  map routes. It also caused over-aggressive behavior, including a bad custom
+  pin hairpin around the city-center roundabout, proving the hook is real but
+  that `0.35` is too low.
+- The vanilla A/B build disabled only the inline multiplier patch and restored
+  obviously different route choices. User confirmed the custom pin returned to
+  the straight city-center roundabout route, while the `0.35` build took the
+  wrong hairpin.
+- Current installed build enables the inline patch with default highway
+  multiplier `0.80` and polls
+  `red4ext/plugins/EdgeWeightGPS/solver_weights.bin` every 500 ms. The file is
+  exactly one little-endian float32 highway multiplier.
+- The inline patch is deliberately broad across the vanilla road-tail branch:
+  reaching `0x40bb98` already means vanilla selected road-style modes `0/2/4`,
+  so we do not hard-gate on `solver+0xc4 == 2`. This avoids creating a manual
+  drive/autodrive disparity. Pedestrian mode `1` uses a different vanilla
+  branch and is not changed by this road-tail patch.
+- Preset writer:
+  `tools/write_solver_weights.py`. Preset binaries live in
+  `presets/solver_weights/`: `vanilla`, `mild`, `default`, `strong`,
+  `proof-highway-cheap`, and `highway-expensive`.
+- Evidence logs:
+  `logs/EdgeWeightGPS_inline_highway035_changed_routes_1449.log` and
+  `logs/EdgeWeightGPS_vanilla_ab_2120.log`.
+
 ## 2026-06-26 Static Update
 
 - Installed RED4ext state is safe: the game plugin directory contains
@@ -110,19 +145,19 @@ Important caveat:
 - Older DLLs are preserved disabled as:
   `Cyberpunk 2077/red4ext/plugins/EdgeWeightGPS/EdgeWeightGPS.dll.disabled`
   and `EdgeWeightGPS.dd1423b.dll.disabled`.
-- Source defaults now enable the full async solver multiplier hook:
-  `kEnableGpsMultiplierHooks = true`.
-- The current behavior patch is deliberately narrow and diagnostic:
-  `DetourGpsNodeMultiplier` hooks native `0x40bb40`, applies only when
-  `job+0xc4 == 2` (driving route mode), reads lane/node flags from
-  `node+0x88`, and multiplies vanilla node edge cost by highway `0.35`,
-  GPSOnly `1.10`, pavement `1.25`, and all other flags `1.0`.
-- `0x40bb00` auxiliary/reverse multiplier is hooked only for signature logging;
-  it is not patched yet.
+- Source defaults enable the inline road-tail patch:
+  `kEnableGpsNodeMultiplierInlinePatch = true`.
+- Source defaults do not enable the old full-function detour:
+  `kEnableGpsMultiplierHooks = false`.
+- Current behavior patch is the inline `0x40bb98` code-cave patch. It preserves
+  vanilla road cost except for highway lanes, whose cost is multiplied by the
+  current `solver_weights.bin` float. Installed default is `0.80`.
+- `solver_weights.bin` lives beside the DLL and is hot-polled every 500 ms.
 - The plugin log was truncated immediately before installing this build.
 - Latest archived test log:
-  `logs/EdgeWeightGPS_spatial_inversion_no_route_change_1845.log`.
-- Game is cold as of the latest user message.
+  `logs/EdgeWeightGPS_vanilla_ab_2120.log`.
+- A cold restart is required after installing a new DLL; changing
+  `solver_weights.bin` after that is hot-reloaded.
 
 ## 2026-06-26 Full Async Solver Findings