diff --git a/docs/ISSUES.md b/docs/ISSUES.md
index 22d6d523..854196d8 100644
--- a/docs/ISSUES.md
+++ b/docs/ISSUES.md
@@ -1183,15 +1183,32 @@ walls** in particular. (Symptoms not fully characterized yet: likely walking thr
 openings that should block / blocking at openings that should pass, and door collision not
 matching the door's open/closed state.)
 
-**Root cause / status (to investigate):** dungeon collision is EnvCell-based — the cell's
-collision BSP + portal openings + per-cell static objects (doors). Candidates: door
-apparatus collision in EnvCells (open/closed BSP swap) not fully ported; portal-opening
-(wall gap) collision geometry handled differently from buildings; the per-cell
-shadow-object registration (A6.P4, see the physics digest) for dungeon EnvCell statics.
-Related families: #32 (edge-slide), #116 (slide-response), the door-collision saga
-(see `feedback_dedup_keys_after_cardinality_change`, `feedback_retail_per_cell_shadow_list`).
-Needs a targeted repro (which door / which opening, expected vs actual) before fixing —
-oracle-first per the physics digest.
+**CHARACTERIZED 2026-07-05 (Facility Hub corridor repro, probe + dat evidence)
+— two stacked mechanisms:**
+1. **PortalSide portal polygons are IN the physics polygon set and we treat
+   them as solid.** Live: running the corridor, the seam crossing
+   `0x8A02016E → 0x8A02017A` (x≈85.25) records a wall hit with normal
+   (−1,0,0) — straight against the movement (`launch-175-verify2.log:42858`).
+   Dat (`Issue137CorridorSeamInspectionTests`): cell 0x8A02016E's portals to
+   0x011E (polys 1/3/5, flags=**PortalSide**, no ExactMatch) are PRESENT in
+   `CellStruct.PhysicsPolygons` — every ExactMatch portal in the same cell is
+   absent from the physics set. The cell's rotation maps those local ±Y portal
+   planes to world ±X — the phantom mid-corridor wall. Retail must honor the
+   portal's SIDE (pass from one side / solid from the other, or pass when the
+   neighbor is loaded); we collide with the raw polygon unconditionally.
+   **Oracle next (MANDATORY before fixing):** grep named-retail for how
+   BSPTREE::find_collisions / CEnvCell treats portal-flagged physics polys
+   (portal_side semantics; the prep note "portal passability comes from BSP
+   structure" was true for ExactMatch portals only).
+2. **The stale sliding normal then wedges all forward motion** (the #116
+   slide-response family): after the single seam hit, EVERY subsequent
+   forward resolve returns `ok=False hit=no` with zero advance — the
+   body-persisted SlidingNormal (−1,0,0) projects the +X offset to exactly
+   zero in AdjustOffset, aborting at step 0 BEFORE any collision test could
+   update the state — an ABSORBING wedge escaped only by strafing ("push
+   through on the side"). Retail re-derives slide state per frame
+   (get_object_info pc:279992 governs only the NEXT frame — #116 notes);
+   audit who clears the body's sliding normal when no contact recurs.
 
 **Files:** `src/AcDream.Core/Physics/` (EnvCell collision, CellTransit, the door apparatus),
 `src/AcDream.Core/Physics/ShadowObjectRegistry.cs` (per-cell registration). See
diff --git a/tests/AcDream.Core.Tests/Physics/Issue137CorridorSeamInspectionTests.cs b/tests/AcDream.Core.Tests/Physics/Issue137CorridorSeamInspectionTests.cs
new file mode 100644
index 00000000..2ea033cd
--- /dev/null
+++ b/tests/AcDream.Core.Tests/Physics/Issue137CorridorSeamInspectionTests.cs
@@ -0,0 +1,90 @@
+using System;
+using System.IO;
+using DatReaderWriter;
+using DatReaderWriter.DBObjs;
+using DatReaderWriter.Options;
+using Xunit;
+using Xunit.Abstractions;
+using Env = System.Environment;
+
+namespace AcDream.Core.Tests.Physics;
+
+/// <summary>
+/// #137 corridor-seam inspection (2026-07-05, Facility Hub). Live probe
+/// evidence (launch-175-verify2.log:42858): crossing corridor cells
+/// 0x8A02016E → 0x8A02017A at world x≈85.25 records a wall hit with normal
+/// (−1,0,0) — pointing straight back against the movement — after which the
+/// stale sliding normal wedges all forward motion (ok=False hit=no, offset
+/// projected to zero). Question this dump answers: does cell 0x8A02017A's
+/// PHYSICS polygon set contain a portal-spanning polygon at its entry plane
+/// (normal ≈ ±X at the portal's local X) — i.e., are portal-sealing polys in
+/// our collision set where retail filters them?
+/// </summary>
+public class Issue137CorridorSeamInspectionTests
+{
+    private readonly ITestOutputHelper _out;
+    public Issue137CorridorSeamInspectionTests(ITestOutputHelper output) => _out = output;
+
+    [Theory]
+    [InlineData(0x8A02016Eu)]
+    [InlineData(0x8A02017Au)]
+    public void CorridorCell_PhysicsPolysAndPortals_DatInspection(uint envCellId)
+    {
+        var datDir = Env.GetEnvironmentVariable("ACDREAM_DAT_DIR")
+            ?? Path.Combine(Env.GetFolderPath(Env.SpecialFolder.UserProfile),
+                            "Documents", "Asheron's Call");
+        if (!Directory.Exists(datDir))
+        {
+            _out.WriteLine($"SKIP: dat directory not found at {datDir}");
+            return;
+        }
+
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+
+        var envCell = dats.Get<EnvCell>(envCellId);
+        Assert.NotNull(envCell);
+        _out.WriteLine($"=== EnvCell 0x{envCellId:X8} ===");
+        _out.WriteLine($"  pos=({envCell!.Position.Origin.X:F2},{envCell.Position.Origin.Y:F2},{envCell.Position.Origin.Z:F2}) " +
+                       $"rot=({envCell.Position.Orientation.X:F3},{envCell.Position.Orientation.Y:F3},{envCell.Position.Orientation.Z:F3},{envCell.Position.Orientation.W:F3})");
+        _out.WriteLine($"  EnvironmentId=0x{envCell.EnvironmentId:X4} CellStructure={envCell.CellStructure}");
+        _out.WriteLine($"  CellPortals={envCell.CellPortals.Count}");
+        foreach (var p in envCell.CellPortals)
+            _out.WriteLine($"    portal poly={p.PolygonId} other=0x{p.OtherCellId:X4} flags={p.Flags}");
+
+        var environment = dats.Get<DatReaderWriter.DBObjs.Environment>(0x0D000000u | envCell.EnvironmentId);
+        Assert.NotNull(environment);
+        Assert.True(environment!.Cells.TryGetValue(envCell.CellStructure, out var cs));
+
+        _out.WriteLine($"  PhysicsPolygons={cs!.PhysicsPolygons.Count} (portal-relevant normals below)");
+        foreach (var (id, poly) in cs.PhysicsPolygons)
+        {
+            // Compute the face normal from the vertex fan (same math as
+            // PhysicsDataCache.ResolvePolygons).
+            var verts = poly.VertexIds;
+            if (verts.Count < 3) continue;
+            if (!cs.VertexArray.Vertices.TryGetValue((ushort)verts[0], out var v0)) continue;
+            if (!cs.VertexArray.Vertices.TryGetValue((ushort)verts[1], out var v1)) continue;
+            if (!cs.VertexArray.Vertices.TryGetValue((ushort)verts[2], out var v2)) continue;
+            var n = System.Numerics.Vector3.Normalize(System.Numerics.Vector3.Cross(
+                v1.Origin - v0.Origin, v2.Origin - v0.Origin));
+
+            // Only print near-horizontal-normal polys (walls) — the seam wall
+            // candidates; floors/ceilings are noise here.
+            if (MathF.Abs(n.Z) > 0.3f) continue;
+            _out.WriteLine($"    poly {id}: n=({n.X:F2},{n.Y:F2},{n.Z:F2}) v0=({v0.Origin.X:F2},{v0.Origin.Y:F2},{v0.Origin.Z:F2}) verts={verts.Count} sides={poly.SidesType} stip={poly.Stippling}");
+        }
+
+        // The portal polygons live in the VISUAL polygon set — print their
+        // ids so overlap with the physics set (same id space?) is visible.
+        _out.WriteLine($"  VisualPolygons={cs.Polygons.Count}");
+        foreach (var p in envCell.CellPortals)
+        {
+            if (cs.Polygons.TryGetValue((ushort)p.PolygonId, out var vp))
+            {
+                _out.WriteLine($"    portal-poly {p.PolygonId} IS in the visual set (verts={vp.VertexIds.Count})");
+                bool inPhysics = cs.PhysicsPolygons.ContainsKey((ushort)p.PolygonId);
+                _out.WriteLine($"    portal-poly {p.PolygonId} in PHYSICS set: {inPhysics}");
+            }
+        }
+    }
+}