#91 thor black rectangle: it's the OWN missile pod -- blakskn now material-keyed

Three testers reported a black rectangle swaying with the footsteps in the
thor cockpit (Summoner = the thr1 label, same THX canopy -- no isolation).
Decode: the inside view is a PER-MECH AUTHORED type-A set, not the cop
alone (no fallback in EntitySegment::GetVideoObjectName -- authored data):
madcat/vulture/bhk1 = cop; sunder/loki/avatar = +tor; thor = +tor +MSL
(the shoulder pod, the reported rectangle); owens = +both legs +tshd.
The pod/leg pilot-facing surfaces use the SAME "<pfx>skin:blakskn_dz_*"
interior-structure material as the canopy frame, but the unlit frame
constant was keyed on the _cop FILENAME -- identical material rendered
(0.13,0.12,0.15) on the canopy and pure (0,0,0) on the pod/legs
([matlog]: owx_cop blakskn vcol=FF211F26 vs owx_lule vcol=FF000000).

Fix (bgfload.cpp): the frame-constant treatment keys on meshIsCop OR
material contains "skin:blakskn_dz_". mechfx:blakskn_mtl (tshd shadow
quads) deliberately excluded. Verified: zero pure-black px in the lower
view band across walk captures, the pod plate renders frame-toned and
blends with the bar at rest (the reported anomaly dissolves), owens legs
read as coherent structure, canopy/terrain un-regressed.

Diags added: BT_MAT_LOG=<stem> per-batch material routing dump (bgfload),
BT_HIDE_INSIDE_SEG=<substr> inside-mesh hide (btl4vid), [view] per-segment
inside-roster names. KB: cockpit-view.md exactly-one claim corrected +
the #91 section; bench scratchpad/night11/thorrect.sh.

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

engine/MUNGA_L4/bgfload.cpp

@@ -640,6 +640,7 @@ struct Builder {
     bool currentTSphere = false;   // material is tsphere_mtl (translocation warp): ramp it despite normals
     bool meshIsTSphere = false;    // this OBJECT is the translocation warp -> smooth-tessellate the cone
     bool meshIsCop = false;        // this OBJECT is a *_cop cockpit canopy shell (task #55)
+    std::string meshStem;          // lowercased load stem (BT_MAT_LOG diag)
     std::map<const void*, int> copRoleMap;  // punch-kit roles per PMESH chunk: 1=mask 2=hull 3=skip (see TAG_PATCH)
     int currentCopRole = 0;                 // role of the pmesh being built (consumed by buildPmesh)
     bool currentHasEmissive = false;
@@ -778,7 +779,19 @@ struct Builder {
         // value is not recoverable from the code (texture-less ramp = no texel
         // luminance to index); default (0.13,0.12,0.15) [T3] matches the dark
         // near-black frame in pod gameplay footage.  BT_COP_FRAME="r g b" overrides.
-        if (useRamp && currentTex.empty() && meshIsCop) {
+        // The same interior-structure treatment applies to the blakskn SKIN
+        // family on ANY mesh, not just *_cop shells: the inside skeletons
+        // author pilot-facing surfaces of the OWN-BODY meshes (thor thx_msl
+        // missile pod, owens owx_* legs -- issue #91) with the identical
+        // "<pfx>skin:blakskn_dz_*" material the canopy frame uses, and the
+        // board shaded them all the same way.  Keying on the filename alone
+        // left those surfaces vcol=pure-black -- the reported "black
+        // rectangle" was the thor pod's blakskn mount plate at RGB(0,0,0)
+        // instead of the frame constant.  mechfx:blakskn_mtl (the tshd
+        // shadow quads) must NOT match -- key on the skin-lib "_dz_" form.
+        const bool blaksknSkin =
+            currentMatName.find("skin:blakskn_dz_") != std::string::npos;
+        if (useRamp && currentTex.empty() && (meshIsCop || blaksknSkin)) {
         	auto CB = [](float ff){ int v=(int)(ff*255.0f+0.5f); return (uint32_t)(v<0?0:v>255?255:v); };
         	vcol = 0xFF000000u | (CB(copFrameRGB(0))<<16) | (CB(copFrameRGB(1))<<8) | CB(copFrameRGB(2));
         }
@@ -939,6 +952,28 @@ struct Builder {
             else
                 batch.lodBias = 0.0f;
             mesh->batches.push_back(batch);
+            // #91 diag: BT_MAT_LOG=<substr> dumps each batch of a matching mesh
+            // stem -- the material routing decision (ramp vs lit vs emissive,
+            // resolved colour, texture) for the inside-view black-mesh hunt.
+            {
+                static const char* s_matLog = getenv("BT_MAT_LOG");
+                if (s_matLog && *s_matLog
+                    && meshStem.find(s_matLog) != std::string::npos)
+                    fprintf(stderr, "[matlog] %s mat=%s color=%08X hasDiff=%d "
+                        "tex='%s' ch=%d hasRamp=%d useRamp=%d norms=%d "
+                        "emis=%d vcol=%08X tris=%u\n",
+                        meshStem.c_str(), currentMatName.c_str(), currentColor,
+                        (int)currentHasDiffuse, currentTex.c_str(),
+                        currentTexChannel, (int)currentHasRamp, (int)useRamp,
+                        (int)hasNormals(vtag), (int)pureEmissive, vcol,
+                        idxCount / 3);
+                if (s_matLog && *s_matLog
+                    && meshStem.find(s_matLog) != std::string::npos)
+                    fprintf(stderr, "[matlog]   ramp lo=(%.3f,%.3f,%.3f) "
+                        "hi=(%.3f,%.3f,%.3f)\n",
+                        currentRampLo[0], currentRampLo[1], currentRampLo[2],
+                        currentRampHi[0], currentRampHi[1], currentRampHi[2]);
+            }
             if (getenv("BT_COP_DUMP") && currentHasRamp && currentTex.empty()) {
                 float lo[3]={1e9f,1e9f,1e9f}, hi[3]={-1e9f,-1e9f,-1e9f}, cen[3]={0,0,0}; int nv=0;
                 for (uint32_t i = idxStart; i < idxStart + idxCount; ++i) {
@@ -1386,6 +1421,7 @@ bool LoadBgfFile(const std::string& name, BgfData& out) {
     // single-siding + dark-frame ramp reconstruction in emitTri/buildPmesh applies to
     // these meshes only.
     b.meshIsCop = stemLower(name).find("_cop") != std::string::npos;
+    b.meshStem = stemLower(name);
     b.res = &res;
     for (const Chunk& c : roots) b.collect(c);
     b.finish();