refactor(physics): delete the redundant pre-sweep slope projection (AD-10 retired)

Stage 0's measurement (previous commit) says the projection is redundant,
so AD-10 retires by deletion rather than by narrowing.

The measurement. With the sample forced to null at BOTH fork sites, from a
clean build:

  * a remote running 30 ticks down a 31-degree walkable ramp produces a
    BIT-IDENTICAL trajectory, position for position;
  * on an 8.4-degree ramp the two differ by at most 2.8e-5 m in Z after 30
    ticks (0.03 mm) and are identical in X and Y — float ordering noise
    from projecting twice against the same plane rather than once;
  * the whole AcDream.Runtime.Tests suite is unchanged.

That is what redundancy looks like, and the arithmetic explains it. The
boundary projection and Transition.AdjustOffset are the same operation
(v -= N * dot(v, N)) against the same plane, and the composition is
idempotent: a vector already on the plane has dot(v, N) == 0, so the
sweep's own projection is a no-op on an already-projected offset and the
full-strength projection on an unprojected one. Either alone produces the
same offset. On terrain a THIRD mechanism, ValidateWalkable's push-out,
re-seats the sphere on the plane every sub-step regardless.

Deleted:
  * both RuntimeRemotePhysicsUpdater sample sites (the host and no-host
    fork branches carried the block verbatim — the AP-22 shape, a row
    naming one site where two exist);
  * the terrainNormal parameter and projection block on
    RemoteMotionCombiner.ComposeOffset;
  * the same block on ComputeOffset, which has no production callers but
    held a second copy of the divergence, so leaving it would have made
    the row's retirement false;
  * PhysicsEngine.SampleTerrainNormal, now callerless.

Removing the parameter rather than passing null is deliberate: it is what
makes a future one-site-only regression a compile error instead of a
silent half-fix.

Two tests went with it —
ComputeOffset_RootMotionFallback_SlopedTerrainNormal_ProjectsZOntoSlope and
its flat-ground twin. Both were weak on their own terms: they drove the
production-dead ComputeOffset and computed their expected values by
re-implementing the projection formula, so they could catch a wrong
MULTIPLY but never a wrong PLANE — which is exactly what the divergence
was. The surviving coverage is geometric and runs the production tick.

Three claims in the old row did not survive contact with the code and are
recorded in the retired row rather than quietly dropped: the justification
(remotes do run the sweep); the description of ComposeOffset's guard as
"interpolation-active" when the code reads `if (!interpolationOverwrote`;
and the roof clause, stale since Bug B gated the sample on OnWalkable —
a steep roof is OnWalkable == false, so the path never ran on #32's
geometry. The retail anchor is corrected too: pc:272296-272346 truncated
both the sliding-normal validity gate at the head and the entire safety
push-out block at the tail. The whole function is 0x0050a370,
pc:272271-272393.

This does not fix #32 and does not partially fix it. #32's remote half was
already closed at 204d0ae0. What deletion does improve is the case #32
never covered: a remote on a WALKABLE non-terrain surface — a bridge, a
dock, a gentle roof, a ramp inside a building — where the terrain sample
returned the plane of the ground far below and applied a wrong plane
rather than none. That surface now gets the body's own committed contact
plane, because that is the only projection left.

The planning contract this work executed is committed alongside as
docs/research/2026-08-06-ad10-contract.md.

Release build 0 errors. Complete solution suite 11,196 passed / 4 skipped
/ 0 failed against the ef976c6d baseline of 11,195 / 4 / 0 — reconciled
exactly as +3 new Runtime tests and -2 deleted Core tests.

Visual gate outstanding: G1 (the ~5 Hz staircase on rolling terrain) is
the veto criterion and runs first; then slope-descent smoothness, a
walkable non-terrain surface, the #32 roof scenario, and flat ground.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/ISSUES.md

@@ -10387,6 +10387,13 @@ other pieces that are either incomplete or unverified for remotes:
   project against, so even a corrected `OnWalkable` would need a real
   contact-plane-derived slide, not the terrain-only approximation AD-10
   already flags as a divergence.
+  **Superseded 2026-08-06:** AD-10 was RETIRED BY DELETION, and this
+  paragraph's premise turned out to be inverted. Remote bodies DO run the full
+  sweep (`ResolveWithTransition` -> `Transition.AdjustOffset`, retail
+  `CTransition::adjust_offset` 0x0050a370 per sub-step), so the roof slide was
+  already driven by a real contact-plane projection; the terrain sample was an
+  EXTRA, non-retail layer on top of it and is now gone. Measured redundant
+  before deletion — see the retired register row.
 
 The investigation stopped there per project policy and instrumented a probe
 (`ACDREAM_PROBE_REMOTE_LANDING`, then the `[remote-slide-*]` family in
@@ -10537,11 +10544,15 @@ pass that recorded them.**
 Still open on this row: the two dependencies named above. **#173**'s remote
 collision-velocity reflect now genuinely runs on a steep contact (the old code
 passed `IsOnGround` as `nowOnWalkable`, which suppressed the reflect exactly
-where retail forces it), but its visual gate is still unrun. **AD-10**'s
+where retail forces it), but its visual gate is still unrun. ~~**AD-10**'s
 terrain-only slope projection still cannot see building geometry; it is now
 correctly gated OFF while the body is not on walkable ground, so a roof slide
 is driven by gravity plus the sweep's own plane projection rather than by that
-approximation. The retail-strict `step_up_slide`/`cliff_slide` audit that this
+approximation.~~ **Closed 2026-08-06:** AD-10 was retired by deletion — the
+terrain-only projection no longer exists anywhere in the tree, so this
+dependency is discharged rather than merely gated. The roof slide is driven by
+gravity plus the sweep's own contact-plane projection, which is what retail
+does. The retail-strict `step_up_slide`/`cliff_slide` audit that this
 row was originally filed for is unchanged.
 
 ---