fix(#171): sticky deep-overlap back-off sign pin — the runaway-to-center (gate-2 residual)

Gate 2: pack behavior good except "sometimes the monster is in the
character / too close vs retail". The ACDREAM_PROBE_STICKY capture
nailed it frame-by-frame: 1661 deep-overlap AdjustOffset ticks, ALL
steering inward (dist -0.65 -> -0.78 -> ... -> -1.9 at +0.13/tick),
monsters converging to centerDist~0 — while the suppressed-snap lines
show ACE's authoritative positions stayed properly OUTSIDE (drift up to
7.7 m). The radii were correct (tgtR=0.68, ownR=0.59-0.98).

Root cause: ACE's literal decode of StickyManager::adjust_offset
(`if (delta >= |dist|) delta = dist;`) leaves delta POSITIVE when the
overlap exceeds one tick's step — steering TOWARD the target center, a
runaway whose equilibrium is centers-coincident. ACE servers virtually
never reach that branch (quantum >=1/30 -> threshold ~1 m); at
render-rate quanta the threshold is ~0.13 m and pack jostle trips it
constantly. The BN mush (0x00555554-0x00555597) is unreadable on
exactly this compare; the retail oracle (side-by-side on the same ACE:
monsters separate) refutes the ACE-literal reading.

Pin: sign-correct clamp — `else if (dist < 0) delta = -delta` (back off
rate-limited). Identical to ACE-literal in every shallow/outside case.
Register row AP-82 (same commit) with the cdb verification note.
Conformance: StickyManagerTests.AdjustOffset_DeepOverlap_BacksOff_
RateLimited. Full suite 4039 green.

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

tests/AcDream.Core.Tests/Physics/Motion/StickyManagerTests.cs

@@ -191,6 +191,26 @@ public sealed class StickyManagerTests
         Assert.Equal(-0.4f, frame.Origin.X, 3);
     }
 
+    [Fact]
+    public void AdjustOffset_DeepOverlap_BacksOff_RateLimited()
+    {
+        var world = new Dictionary<uint, R5Host>();
+        var self = new R5Host(10u, world) { Radius = 0.5f, MinterpMaxSpeed = 1.0f };
+        var target = new R5Host(20u, world);
+        // centerDist 0.1 → cyl = 0.1-0.5-0.5 = -0.9, minus 0.3 → dist = -1.2
+        // (overlap DEEPER than one tick's step).
+        var sticky = StuckAndInitialized(self, target, new Vector3(0.1f, 0f, 0f));
+
+        var frame = new MotionDeltaFrame();
+        sticky.AdjustOffset(frame, quantum: 0.1);
+
+        // delta = 5*0.1 = 0.5 < |dist|=1.2 — ACE's literal branch kept +0.5
+        // here (INWARD: the #171 gate-3 runaway-to-center; 1661 probe ticks,
+        // all inward, equilibrium at centers-coincident). The sign pin backs
+        // off rate-limited: dir +X × −0.5.
+        Assert.Equal(-0.5f, frame.Origin.X, 3);
+    }
+
     [Fact]
     public void AdjustOffset_UsesCachedPosition_WhenTargetUnresolvable()
     {