diag(physics): remote landing-edge probe; record the two live jump defects

The user live-tested route 4a and reported two defects on player remotes: a
remote holds the falling animation after landing before finally landing, and a
remote jumping onto a house plants on the roof where retail slides off, then
blips to the slid-down position.

Neither is a route 4a regression. Do NOT revert 44830a0e — reverting would
restore the per-packet render slam 4a removed without touching either defect.

Bug B's root cause is identified and already covered by open issue #32, whose
text names both symptoms in one sentence. Both landing sites assert
TransientState |= Contact | OnWalkable unconditionally, where retail derives it
from the contact plane — CPhysicsObj::SetPositionInternal @0x00515330
(`if (contact_plane.N.z < floor_z) set_on_walkable(0) else set_on_walkable(1)`).
A steep roof is contact but NOT on_walkable; asserting both suppresses the slide
response, so the body sits until the server's positions walk 4 m away and
AP-87's threshold snaps it. That is the blip. Verified byte-identical pre-4a via
`git show 19d95094:`.

Bug B's *visible shape* IS 4a's: pre-4a every packet slammed the render entity
to the wire pose, so a stuck body flickered toward the true sliding position
5-10x per second — jitter rather than a clean hold.

Bug A stops at the goal's stop-condition rather than getting a speculative fix.
Three hypotheses with non-overlapping fixes; picking wrong means changing a
retail-ported gate on a guess. Retail's mechanism is already fully decoded, so
what is missing is OUR runtime state — no cdb trace against retail is needed.

Adds ACDREAM_PROBE_REMOTE_LANDING (PhysicsDiagnostics, read once at startup per
the diagnostic-owner rule, one bool check when off). It logs both landing sites
immediately before HitGround, and — the most diagnostic signal — emits a
separate line when a site is reached but the gravity gate is about to no-op,
which is hypothesis 1 (a wholesale Body.State write wiping the transient Gravity
bit mid-air, exactly AP-81's stated risk). Temporary instrumentation, marked for
stripping once the evidence is in.

Evidence recorded rather than new bugs filed: #32 gains the observation, the
root cause and the #173/AD-10 dependency caveat; AP-87 gains a live instance of
its stated risk; AD-10's stale file:line is corrected to RemoteMotionCombiner
with a note that its terrain-only normal cannot see a house roof at all.

Also files #308 — a SECOND flaky test, distinct from #302, which was twice
misattributed to it before being written down. #302 is a GC-allocation assertion
in App.Tests; #308 is a wall-clock deadline loop in Core.Net.Tests that fails
only under full-suite CPU contention (0 failures in 4 isolated runs). Conflating
them hides one, and an agent told to "ignore the known flake" would wave through
a real transport regression.

Gates: complete Release solution 10,938 passed / 4 skipped / 0 failed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/AcDream.App/Physics/LiveEntityNetworkUpdateController.cs

@@ -1860,6 +1860,34 @@ internal sealed class LiveEntityNetworkUpdateController
                     {
                         _motionRuntime.EnsureRemoteMotionBindings(rmState, aeForLand, update.Guid);
                     }
+
+                    // Bug A investigation (2026-08-04, docs/ISSUES.md #32):
+                    // capture the exact state HitGround is about to act on —
+                    // see PhysicsDiagnostics.LogRemoteLanding for the field
+                    // list and PhysicsDiagnostics.ProbeRemoteLandingEnabled
+                    // for the discriminator table. TEMPORARY — strip once
+                    // the live-test run has landed.
+                    if (AcDream.Core.Physics.PhysicsDiagnostics.ProbeRemoteLandingEnabled)
+                    {
+                        bool gravitySetForProbe = rmState.Body.HasGravity;
+                        AcDream.Core.Physics.PhysicsDiagnostics.LogRemoteLanding(
+                            site: "controller",
+                            guid: update.Guid,
+                            airborneBefore: true,
+                            gravitySet: gravitySetForProbe,
+                            contact: rmState.Body.InContact,
+                            onWalkable: rmState.Body.OnWalkable,
+                            hasDefaultSink: rmState.Motion.DefaultSink is not null,
+                            resolveIsOnGround: null,
+                            sequencerStyle: aeForLand?.Sequencer?.CurrentStyle ?? 0,
+                            sequencerMotion: aeForLand?.Sequencer?.CurrentMotion ?? 0);
+                        if (!gravitySetForProbe)
+                        {
+                            AcDream.Core.Physics.PhysicsDiagnostics.LogRemoteLandingGateNoOp(
+                                "controller", update.Guid);
+                        }
+                    }
+
                     ulong landingStateAuthorityVersion =
                         positionRecord.StateAuthorityVersion;
                     rmState.Movement.HitGround();