Add live-tunable GPS solver highway weight

docs/traffic-system-debrief.md

@@ -980,32 +980,62 @@ the original symptom: the solver is weighted enough to avoid obviously invalid
 surfaces, but it has no strong reason to stay on highway corridors for long
 vehicle trips.
 
-The current RED4ext prototype therefore hooks `0x40bb40` and only changes
-driving-mode calls (`solver/job + 0xc4 == 2`). It reads flags from
-`node+0x88`, leaves vanilla results intact for ordinary roads and unknown
-surfaces, and applies this diagnostic multiplier set:
+The first RED4ext prototype tried to hook `0x40bb40` as a normal C++ detour.
+That found the correct function but crashed during load-time GPS warmup because
+the optimized caller expects the tiny vanilla helper not to disturb volatile
+register state used immediately afterward.
+
+The stable prototype now patches inline at the road-tail block `0x40bb98`
+instead. Reaching that block already means the vanilla function selected one of
+the road-style modes `0/2/4`; pedestrian mode `1` uses a different branch. The
+patch preserves vanilla `node+0x93` behavior, checks `node+0x88 & 0x4000`, and
+applies an extra multiplier only for highway lanes.
+
+The proof multiplier was:
 
 ```text
 Highway  0.35
-GPSOnly  1.10
-Pavement 1.25
-Other    1.00
 ```
 
-`0x40bb00` is currently hooked only for signature logging. If the node
-multiplier test moves routes but produces weird reverse/turnaround behavior,
-the next step is to tune or gate the auxiliary multiplier as well.
+Live A/B testing confirmed this is the decisive world-map route-cost lever.
+With `0.35`, routes visibly changed and a custom pin around the city-center
+roundabout took an obviously bad highway/ramp hairpin. With the inline patch
+disabled, the same route returned to the straight vanilla path through the
+roundabout.
+
+The current installed build uses a default highway multiplier of `0.80` and
+hot-reloads `solver_weights.bin` from the plugin directory. The file is exactly
+one little-endian float32. `tools/write_solver_weights.py` writes the installed
+file and can generate named presets:
+
+```text
+vanilla              1.00
+mild                 0.90
+default              0.80
+strong               0.70
+proof-highway-cheap  0.35
+highway-expensive    3.00
+```
+
+The patch intentionally does not hard-gate on `solver+0xc4 == 2`, because
+autodrive-like local vehicle navigation may use another road-style mode. Since
+the patch lives in the vanilla road-tail branch, it applies to road-style modes
+`0/2/4` and still leaves pedestrian mode `1` alone.
+
+`0x40bb00` is not patched yet. If tuned highway weights still produce
+reverse/turnaround artifacts, inspect or patch that auxiliary multiplier so
+reverse/special progress branches receive a compatible policy.
 
 ## Future Improvements
 
 Better versions of this mod could:
 
-- tune the `0x40bb40` solver multiplier after live A/B testing confirms visible
-  route changes
+- tune the `0x40bb98` inline highway multiplier from the current `0.80` default
+  using live `solver_weights.bin` presets
 - inspect and, if needed, patch `0x40bb00` so reverse/special progress branches
   receive the same road-class policy as forward expansion
-- add a tiny live-tuning file for the solver multipliers, similar to the earlier
-  `spatial_weights.bin`, once the hook is confirmed stable
+- extend `solver_weights.bin` beyond one highway float only if GPSOnly/pavement
+  tuning becomes necessary
 - replace the crashing `0x8d46cc` detour with a narrower inline patch or a
   safer caller-side hook
 - decode enough of the `VAND` graph to join navigation points to traffic lane