From 7a244b3291b6ef45675ffcff2905523bd927cd46 Mon Sep 17 00:00:00 2001
From: Erik <erik.nihlen@gmail.com>
Date: Fri, 29 May 2026 20:35:26 +0200
Subject: [PATCH] =?UTF-8?q?fix(physics):=20Phase=20A8.F=20=E2=80=94=20view?=
 =?UTF-8?q?er=20sweeps=20bypass=20the=2030-step=20cap=20(retail-faithful)?=
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Retail's CTransition::find_transitional_position (:273613) has no step
cap. calc_num_steps (:272149) has a dedicated viewer branch `if ((state
& 4) != 0)` at :272181 for sight/viewer objects (ObjectInfoState.IsViewer
= 0x4). The existing acdream cap correctly had a comment "Sight objects
bypass this" but the bypass was never wired — no IsViewer caller existed
until the A8.F camera spring-arm.

With radius 0.3 m the cap fires at ~9 m. The spring-arm sweeps up to
40 m (≈134 steps), so zoomed-out cameras snapped to the player's head
instead of sweeping through geometry. The fix adds `&& !ObjectInfo.IsViewer`
to the guard; non-viewers keep the 30-step safety net (player spheres
~0.48 m radius never exceed 14 m/tick).

Conformance test: radius=0.3, dist=12 (40 steps > 30 cap) over flat
terrain. Normal mover bails (Assert.False). Viewer proceeds to target
(Assert.True + CurPos.X > from.X). RED → GREEN.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/AcDream.Core/Physics/TransitionTypes.cs   | 10 +++++--
 .../Physics/TransitionTests.cs                | 28 +++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/src/AcDream.Core/Physics/TransitionTypes.cs b/src/AcDream.Core/Physics/TransitionTypes.cs
index eb93665..f947a67 100644
--- a/src/AcDream.Core/Physics/TransitionTypes.cs
+++ b/src/AcDream.Core/Physics/TransitionTypes.cs
@@ -698,8 +698,14 @@ public sealed class Transition
             offsetPerStep = Vector3.Zero;
         }
 
-        // Retail safety cap (30 steps). Sight objects bypass this.
-        if (numSteps > PhysicsGlobals.MaxTransitionSteps)
+        // Retail safety cap (30 steps). Viewer/sight objects bypass it, matching
+        // retail: CTransition::find_transitional_position (acclient_2013_pseudo_c.txt
+        // :273613) has no cap, and calc_num_steps (:272149) has a dedicated viewer
+        // branch `if ((state & 4) != 0)` at :272181. The A8.F camera spring-arm
+        // (IsViewer) sweeps the eye far past 30 steps; the zoom clamp (≤40 m / 0.3 m
+        // radius ≈ 134 steps) bounds it. Non-viewers keep the safety net (players
+        // never exceed it: 30 × 0.48 m ≈ 14 m/tick).
+        if (numSteps > PhysicsGlobals.MaxTransitionSteps && !ObjectInfo.IsViewer)
             return false;
 
         // Apply free rotation if requested.
diff --git a/tests/AcDream.Core.Tests/Physics/TransitionTests.cs b/tests/AcDream.Core.Tests/Physics/TransitionTests.cs
index 307def0..7feb991 100644
--- a/tests/AcDream.Core.Tests/Physics/TransitionTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/TransitionTests.cs
@@ -283,6 +283,34 @@ public class TransitionTests
             $"Sphere bottom {bottom:F4} should be >= terrain {groundZ}");
     }
 
+    [Fact]
+    public void FindTransitionalPosition_LongSweep_ViewerBypassesStepCap()
+    {
+        // A8.F: the 30-step safety cap bailed long sweeps. Retail's
+        // find_transitional_position has no cap and handles viewers specially
+        // (calc_num_steps `state & 4` branch, acclient :272181). The camera
+        // spring arm (IsViewer) must not bail. radius 0.3, dist 12 → 40 steps > 30.
+        const float groundZ = 10f;
+        var engine = MakeEngine(FlatTerrain(groundZ));
+
+        Vector3 from = new(50f, 50f, groundZ);
+        Vector3 to   = new(62f, 50f, groundZ);  // 12 units → 40 steps at r=0.3 (>30 cap)
+
+        // Normal mover: hits the 30-step cap, bails without moving.
+        var normal = MakeTransition(from, to, sphereRadius: 0.3f);
+        bool normalOk = normal.FindTransitionalPosition(engine);
+        Assert.False(normalOk);
+
+        // Viewer: cap bypassed → sweep proceeds the full distance over flat ground.
+        var viewer = MakeTransition(from, to, sphereRadius: 0.3f);
+        viewer.ObjectInfo.State |= ObjectInfoState.IsViewer;
+        bool viewerOk = viewer.FindTransitionalPosition(engine);
+        Assert.True(viewerOk);
+        // Position must have advanced toward `to` (key invariant: viewer proceeds).
+        Assert.True(viewer.SpherePath.CurPos.X > from.X,
+            "Viewer sphere should have advanced in +X past the step cap");
+    }
+
     [Fact]
     public void SampleTerrainZ_FindsCorrectLandblock()
     {