test(graphics): one coverage matrix, run per machine, with a third outcome

.agents/tools/graphics/build-in-subos.sh

@@ -63,7 +63,19 @@ rm -rf "$STAGE"
 mkdir -p "$SRC" "$STAGE"
 
 # ── fetch ───────────────────────────────────────────────────────────────
-TARBALL="$SRC/$(basename "$URL")"
+# Cached under NAME-VERSION, not under the URL's basename.
+#
+# Every GitHub archive URL is `.../archive/refs/tags/v<tag>.tar.gz`, so the
+# basename carries the tag and nothing about the project. Vulkan-Headers and
+# Vulkan-Loader are both released as v1.4.313, so the second build found the
+# first one's `v1.4.313.tar.gz` already in $SRC, skipped the download, and
+# configured, built, staged, leak-checked and PACKAGED the wrong source --
+# producing a `vulkan-loader` payload containing Vulkan-Headers, with every step
+# reporting success. It was caught only because the resulting package had no
+# lib/ directory.
+#
+# The basename is kept as a suffix so the file is still recognisable on disk.
+TARBALL="$SRC/${NAME}-${VERSION}-$(basename "$URL")"
 [[ -f "$TARBALL" ]] || {
     log "fetching $(basename "$URL")"
     curl -fsSL --retry 3 -o "$TARBALL" "$URL" || fail "download failed"
@@ -189,7 +201,22 @@ for dep in $DEPS; do
         fail "--deps $dep: not installed in $XHOME (xlings install $dep)"
     fi
     log "  dep $dep -> ${depdir#"$XHOME"/data/xpkgs/}"
-    if [[ -d "$depdir/lib/pkgconfig" ]]; then
+    # BOTH pkgconfig locations, and the second one is not a nicety.
+    #
+    # `lib/pkgconfig` is where a library puts its .pc. A PROTOCOL-ONLY package
+    # installs no library at all and puts its .pc in `share/pkgconfig` --
+    # xorgproto ships 40 of them there (xineramaproto, damageproto, ...), and
+    # xcb-proto is the same shape.
+    #
+    # Looking only at `lib/` therefore made every protocol package invisible to
+    # pkg-config while its HEADERS were still spliced in by `-I` below. That
+    # combination is why the gap survived: mesa builds fine, because it includes
+    # the headers and never asks pkg-config for a protocol module. libXinerama
+    # does ask, and dies on `XINERAMA_CFLAGS ... no such package` for a package
+    # that is sitting right there and whose headers are already on the command
+    # line.
+    for pcsrc in "$depdir/lib/pkgconfig" "$depdir/share/pkgconfig"; do
+        [[ -d "$pcsrc" ]] || continue
         # Rewrite `prefix=` into a scratch copy rather than use the payload's
         # .pc as-is. libxml2's ships `prefix=/tmp/libxml2-install` — the
         # directory it was built in, on a machine that no longer exists — so
@@ -202,12 +229,15 @@ for dep in $DEPS; do
         # as far as a build is concerned.
         pcdir="$WORK/pc/$dep"
         mkdir -p "$pcdir"
-        for pc in "$depdir"/lib/pkgconfig/*.pc; do
+        for pc in "$pcsrc"/*.pc; do
             [[ -e "$pc" ]] || continue
             sed "s#^prefix=.*#prefix=${depdir%/}#" "$pc" > "$pcdir/$(basename "$pc")"
         done
-        PKG_CONFIG_LIBDIR="$PKG_CONFIG_LIBDIR:$pcdir"
-    fi
+        case ":$PKG_CONFIG_LIBDIR:" in
+            *":$pcdir:"*) ;;
+            *) PKG_CONFIG_LIBDIR="$PKG_CONFIG_LIBDIR:$pcdir" ;;
+        esac
+    done
     [[ -d "$depdir/include" ]] && CPPFLAGS="$CPPFLAGS -I$depdir/include"
     if [[ -d "$depdir/lib" ]]; then
         # A staged copy with an RPATH, not the payload itself.

.agents/tools/graphics/vendorprobe.c

@@ -0,0 +1,20 @@
+/* Does glvnd's vendor actually load, and does its entry point exist?
+ *
+ * S1 fails with zero vendors and mesa printing nothing, which narrows the
+ * failure to glvnd's load-then-__egl_Main step. Everything upstream of it was
+ * eliminated by measurement (namespaces, /usr, /dev, /sys, the dependency
+ * closure, JSON readability). This asks the one remaining question directly. */
+#include <dlfcn.h>
+#include <stdio.h>
+int main(int argc, char **argv) {
+    if (argc < 2) { fprintf(stderr, "usage: vendorprobe <vendor.so>\n"); return 2; }
+    void *h = dlopen(argv[1], RTLD_LAZY | RTLD_LOCAL);
+    if (!h) { printf("DLOPEN=fail\nERR=%s\n", dlerror()); return 1; }
+    printf("DLOPEN=ok\n");
+    dlerror();
+    void *m = dlsym(h, "__egl_Main");
+    const char *e = dlerror();
+    printf("EGL_MAIN=%s\n", m ? "present" : "MISSING");
+    if (e) printf("DLSYM_ERR=%s\n", e);
+    return 0;
+}