diff --git a/docs/ISSUES.md b/docs/ISSUES.md
index e5fe597b..83fa0294 100644
--- a/docs/ISSUES.md
+++ b/docs/ISSUES.md
@@ -5482,6 +5482,27 @@ outdoors at the angle that previously erased it.
 
 # Recently closed
 
+## #150 — Open doors still blocked at the threshold (ethereal target not skipped in the step-down pass)
+
+**Status:** DONE (2026-06-25) — after the retail collision sweep, an OPEN door
+(ETHEREAL_PS 0x4 set on Use) still stopped the player with a small residual block at
+the sill ("can-sized cylinder on the ground threshold"), even though the door swings
+open visually. Root: the resolver runs two collision passes per step — the main
+sweep and a step-down (foot-sphere "is there floor?") sub-pass. acdream tested the
+ethereal door in BOTH; the main pass cleared it (Layer-1 Path-1 + the Layer-2
+override) but the **step-down pass had no escape** and its `Collided` result survived
+as the threshold block. Retail's `CPhysicsObj::FindObjCollisions` (pc:276795-276806)
+SKIPS an ethereal target entirely when `sphere_path.step_down != 0` — it only tests
+it in the main pass — so an open door is fully passable everywhere (the swung panel's
+position is irrelevant; ethereal = no collision, the animation is purely visual).
+Fix: port that exact branch — `if ((state & 0x4) || (mover.Ethereal && (state & 0x1)
+== 0)) && sp.StepDown → continue`. `TransitionTypes.cs` per-object loop. Live-verified
+(user "Yes it works"; the door now blocks 0× while open [0x1000C], still blocks while
+closed [0x10008]; pre-fix it blocked 217× while open). Core suite green (1595/0). The
+earlier "animate the door collision" theory was WRONG and dropped — the user correctly
+noted that if collision followed the swung panel you'd bump the panel in its open
+position, which retail does not do. Likely also advances the door half of #137.
+
 ## #149 — BSP-less landblock statics (torches/braziers/lamp-posts) were walk-through
 
 **Status:** DONE (2026-06-25, `4cf6eeb`) — town props placed as landblock stabs
diff --git a/src/AcDream.Core/Physics/TransitionTypes.cs b/src/AcDream.Core/Physics/TransitionTypes.cs
index 7b0aeafb..a633efd4 100644
--- a/src/AcDream.Core/Physics/TransitionTypes.cs
+++ b/src/AcDream.Core/Physics/TransitionTypes.cs
@@ -2599,15 +2599,32 @@ public sealed class Transition
             if (CollisionExemption.ShouldSkip(obj.State, obj.Flags, ObjectInfo.State))
                 continue;
 
-            // Task 3 (2026-06-24): set obstruction_ethereal on SpherePath before
-            // the shape dispatch. Retail: CPhysicsObj::FindObjCollisions pc:276806 /
-            // 0x0050f0c9 — `ebx->sphere_path.obstruction_ethereal = var_c` where
-            // var_c=1 when the target has ETHEREAL_PS (0x4). The flag is consumed by
-            // BSPQuery Path 1 (BSPTREE::find_collisions pc:323742) to route through
-            // sphere_intersects_solid instead of the blocking paths, making the player
-            // passable through the open door's BSP (no solid leaf at the opening).
-            // Cleared after each per-object test below (retail pc:276989 / 0x0050f31e).
-            sp.ObstructionEthereal = (obj.State & 0x4u) != 0;
+            // Retail CPhysicsObj::FindObjCollisions ethereal branch
+            // (pc:276795-276806 / 0x0050f0a2-0x0050f0c9). A target counts as
+            // "ethereal for this test" when it has ETHEREAL_PS (0x4) OR the mover
+            // is ethereal against a NON-static target ((state & 1) == 0):
+            //
+            //   if ((state & 4) || (mover.ethereal && (state & 1) == 0)) {
+            //       var_c = 1;
+            //       if (sphere_path.step_down == 0) goto do_test;   // main pass
+            //       // step_down != 0 → fall through = SKIP this target entirely
+            //   } else { var_c = 0; do_test: obstruction_ethereal = var_c; ...test... }
+            //
+            // The step-down SKIP (pc:276799 — no `goto` when step_down != 0) is what
+            // makes an OPEN DOOR fully passable: the main pass tests it with
+            // obstruction_ethereal=1 (BSPQuery Path 1 + the Layer-2 override below
+            // force it to OK), and the foot-sphere step-down sub-pass NEVER TESTS IT
+            // at all. acdream previously tested ethereal targets in BOTH passes with
+            // no step-down escape, so the step-down pass left a residual threshold
+            // block ("can" at the open door's sill) that retail does not have
+            // (#137 / live capture 2026-06-25: 217 blocks all while door state=0x1000C).
+            // obstruction_ethereal (= retail var_c) is consumed by BSPQuery Path 1
+            // (BSPTREE::find_collisions pc:323742); cleared after each test (pc:276989).
+            bool etherealForTest = (obj.State & 0x4u) != 0
+                                || (ObjectInfo.Ethereal && (obj.State & 0x1u) == 0);
+            if (etherealForTest && sp.StepDown)
+                continue;   // retail pc:276799 — ethereal target not tested in step-down
+            sp.ObstructionEthereal = etherealForTest;
 
             // L.2a slice 3 (2026-05-12): snapshot collision-normal state so
             // we can tell whether THIS object's BSP/CylSphere test produced a