Add accuracy mode and GLIBC 2.41 release builds

Add default-off PreferAccuracy with conservative native variants for every RDNA3/RDNA4 target and a separate JIT cache. Preserve fast defaults and reject mixed accuracy sets.

Add a pinned Debian build environment, rebuild all release components against GLIBC 2.41, and include toolchain provenance and release notes for the accuracy changes and the preceding artifact/synchronization fixes. Refs #6; CPU-overhead confirmation for #7 remains pending.

tools/d4r_native_selection.h

@@ -0,0 +1,91 @@
+/* Native directory selection shared with the CPU-only configuration tests. */
+#pragma once
+#include <dirent.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static int d4r_apply_accuracy_policy(void)
+{
+    const char* prefer = getenv("D4R_PREFER_ACCURACY");
+    if (prefer == NULL || strcmp(prefer, "1") != 0)
+        return 0;
+    setenv("D4R_ZLUDA_IGNORE_DENORMAL", "0", 1);
+    setenv("D4R_ZLUDA_WMMA_F32ACC", "0", 1);
+    setenv("D4R_ZLUDA_FAST_MATH", "0", 1);
+    setenv("D4R_ZLUDA_WAVE64", "0", 1);
+    setenv("D4R_ELIDE_NGX_SYNC", "0", 1);
+    return 1;
+}
+
+static int d4r_accuracy_directory(const char* directory)
+{
+    char path[1200], version[16];
+    if (snprintf(path, sizeof(path), "%s/d4r-accuracy.txt", directory) >= (int)sizeof(path))
+        return 0;
+    FILE* file = fopen(path, "r");
+    if (file == NULL)
+        return 0;
+    const int valid = fgets(version, sizeof(version), file) != NULL && strcmp(version, "1\n") == 0;
+    fclose(file);
+    return valid;
+}
+
+/* 1 = hash-checked set, 2 = unmanifested developer set, 0 = no usable set.
+   Accuracy mode never selects an unmarked directory, including flat legacy developer builds. */
+static int d4r_native_candidate(const char* directory, int accuracy)
+{
+    if (accuracy && !d4r_accuracy_directory(directory))
+        return 0;
+    char path[1200];
+    if (snprintf(path, sizeof(path), "%s/d4r-kernels.txt", directory) >= (int)sizeof(path))
+        return 0;
+    FILE* file = fopen(path, "r");
+    if (file != NULL)
+    {
+        fclose(file);
+        return 1;
+    }
+    return accuracy ? 2 : 0;
+}
+
+static int d4r_select_native_source(const char* configured, const char* architecture, int accuracy,
+                                  int fp8, char* source, size_t size)
+{
+    char base[1024];
+    const int length = accuracy && !d4r_accuracy_directory(configured)
+        ? snprintf(base, sizeof(base), "%s/accuracy", configured)
+        : snprintf(base, sizeof(base), "%s", configured);
+    if (length < 0 || length >= (int)sizeof(base))
+        return 0;
+    int kind;
+    if (fp8 && strncmp(architecture, "gfx12", 5) == 0)
+    {
+        if (snprintf(source, size, "%s/%s-fp8", base, architecture) >= (int)size)
+            return 0;
+        if ((kind = d4r_native_candidate(source, accuracy)) != 0)
+            return kind;
+    }
+    if (architecture[0] != '\0')
+    {
+        if (snprintf(source, size, "%s/%s", base, architecture) >= (int)size)
+            return 0;
+        if ((kind = d4r_native_candidate(source, accuracy)) != 0)
+            return kind;
+    }
+    if (snprintf(source, size, "%s", base) >= (int)size)
+        return 0;
+    if ((kind = d4r_native_candidate(source, accuracy)) != 0)
+        return kind;
+    if (accuracy)
+        return 0;
+    /* Keep legacy flat developer directories working, but do not hand a release root to ZLUDA. */
+    DIR* directory = opendir(base);
+    if (directory == NULL)
+        return 0;
+    int targets = 0;
+    for (struct dirent* entry; (entry = readdir(directory)) != NULL;)
+        targets += strncmp(entry->d_name, "gfx", 3) == 0;
+    closedir(directory);
+    return targets ? 0 : 2;
+}