refactor: invert FATAL_CHECK logic to standard assertion style

- Inverted FATAL_CHECK macro to crash if condition is FALSE (standard assertion)
- Updated all call sites in audio, GPU, and CNN subsystems
- Updated documentation and examples
- Recorded completion in doc/COMPLETED.md

9 files changed, 28 insertions, 29 deletions

diff --git a/TODO.md b/TODO.md
index 4e67b51..e7aec46 100644
--- a/TODO.md
+++ b/TODO.md
@@ -32,7 +32,6 @@ Enhanced CNN post-processing with multi-dimensional feature inputs.
 
 **Status:**
 - ✅ Full implementation complete and validated
-- ✅ Binary weight loading fixed (FATAL_CHECK inversion bug)
 - ✅ Sigmoid activation (smooth gradients, fixes training collapse)
 - ✅ Training pipeline: patch-based, stable convergence
 - ✅ All tests passing (34/36, 2 unrelated script failures)
diff --git a/cnn_v2/src/cnn_v2_effect.cc b/cnn_v2/src/cnn_v2_effect.cc
index 60538d4..133087a 100644
--- a/cnn_v2/src/cnn_v2_effect.cc
+++ b/cnn_v2/src/cnn_v2_effect.cc
@@ -77,7 +77,7 @@ void CNNv2Effect::load_weights() {
   uint32_t num_layers = header[2];
   uint32_t total_weights = header[3];
 
-  FATAL_CHECK(magic != 0x324e4e43, "Invalid CNN v2 weights magic\n"); // 'CNN2'
+  FATAL_CHECK(magic == 0x324e4e43, "Invalid CNN v2 weights magic\n"); // 'CNN2'
 
   // Support both version 1 (16-byte header) and version 2 (20-byte header with
   // mip_level)
diff --git a/src/audio/backend/miniaudio_backend.cc b/src/audio/backend/miniaudio_backend.cc
index 26194c9..a921453 100644
--- a/src/audio/backend/miniaudio_backend.cc
+++ b/src/audio/backend/miniaudio_backend.cc
@@ -86,7 +86,7 @@ void MiniaudioBackend::audio_callback(ma_device* pDevice, void* pOutput,
   last_frameCount = frameCount;
 
   // Validate device state
-  FATAL_CHECK(!pDevice || pDevice->sampleRate == 0,
+  FATAL_CHECK(pDevice && pDevice->sampleRate != 0,
               "Invalid device in callback!\n");
 
   // Check actual sample rate matches our expectation
@@ -104,7 +104,7 @@ void MiniaudioBackend::audio_callback(ma_device* pDevice, void* pOutput,
   float* fOutput = (float*)pOutput;
 
   // BOUNDS CHECK: Sanity check on frameCount
-  FATAL_CHECK(frameCount > 8192 || frameCount == 0,
+  FATAL_CHECK(frameCount <= 8192 && frameCount > 0,
               "AUDIO CALLBACK ERROR: frameCount=%u (unreasonable!)\n",
               frameCount);
 
diff --git a/src/audio/ring_buffer.cc b/src/audio/ring_buffer.cc
index 54dd25b..b3152a0 100644
--- a/src/audio/ring_buffer.cc
+++ b/src/audio/ring_buffer.cc
@@ -51,7 +51,7 @@ int AudioRingBuffer::write(const float* samples, int count) {
   const int write = write_pos_.load(std::memory_order_acquire);
 
   // BOUNDS CHECK: Validate write position
-  FATAL_CHECK(write < 0 || write >= capacity_,
+  FATAL_CHECK(write >= 0 && write < capacity_,
               "write_pos out of bounds! write=%d, capacity=%d\n", write,
               capacity_);
 
@@ -60,7 +60,7 @@ int AudioRingBuffer::write(const float* samples, int count) {
   if (to_write <= space_to_end) {
     // Write in one chunk
     // BOUNDS CHECK
-    FATAL_CHECK(write < 0 || write + to_write > capacity_,
+    FATAL_CHECK(write >= 0 && write + to_write <= capacity_,
                 "BOUNDS ERROR in write(): write=%d, to_write=%d, capacity=%d\n",
                 write, to_write, capacity_);
     memcpy(&buffer_[write], samples, to_write * sizeof(float));
@@ -68,14 +68,14 @@ int AudioRingBuffer::write(const float* samples, int count) {
   } else {
     // Write in two chunks (wrap around)
     // BOUNDS CHECK - first chunk
-    FATAL_CHECK(write < 0 || write + space_to_end > capacity_,
+    FATAL_CHECK(write >= 0 && write + space_to_end <= capacity_,
                 "BOUNDS ERROR in write() chunk1: write=%d, space_to_end=%d, "
                 "capacity=%d\n",
                 write, space_to_end, capacity_);
     memcpy(&buffer_[write], samples, space_to_end * sizeof(float));
     const int remainder = to_write - space_to_end;
     // BOUNDS CHECK - second chunk
-    FATAL_CHECK(remainder < 0 || remainder > capacity_,
+    FATAL_CHECK(remainder >= 0 && remainder <= capacity_,
                 "BOUNDS ERROR in write() chunk2: remainder=%d, capacity=%d\n",
                 remainder, capacity_);
     memcpy(&buffer_[0], samples + space_to_end, remainder * sizeof(float));
@@ -96,7 +96,7 @@ int AudioRingBuffer::read(float* samples, int count) {
     const int read = read_pos_.load(std::memory_order_acquire);
 
     // BOUNDS CHECK: Validate read position
-    FATAL_CHECK(read < 0 || read >= capacity_,
+    FATAL_CHECK(read >= 0 && read < capacity_,
                 "read_pos out of bounds! read=%d, capacity=%d\n", read,
                 capacity_);
 
@@ -105,7 +105,7 @@ int AudioRingBuffer::read(float* samples, int count) {
     if (to_read <= space_to_end) {
       // Read in one chunk
       // BOUNDS CHECK
-      FATAL_CHECK(read < 0 || read + to_read > capacity_,
+      FATAL_CHECK(read >= 0 && read + to_read <= capacity_,
                   "BOUNDS ERROR in read(): read=%d, to_read=%d, capacity=%d\n",
                   read, to_read, capacity_);
       memcpy(samples, &buffer_[read], to_read * sizeof(float));
@@ -113,14 +113,14 @@ int AudioRingBuffer::read(float* samples, int count) {
     } else {
       // Read in two chunks (wrap around)
       // BOUNDS CHECK - first chunk
-      FATAL_CHECK(read < 0 || read + space_to_end > capacity_,
+      FATAL_CHECK(read >= 0 && read + space_to_end <= capacity_,
                   "BOUNDS ERROR in read() chunk1: read=%d, space_to_end=%d, "
                   "capacity=%d\n",
                   read, space_to_end, capacity_);
       memcpy(samples, &buffer_[read], space_to_end * sizeof(float));
       const int remainder = to_read - space_to_end;
       // BOUNDS CHECK - second chunk
-      FATAL_CHECK(remainder < 0 || remainder > capacity_,
+      FATAL_CHECK(remainder >= 0 && remainder <= capacity_,
                   "BOUNDS ERROR in read() chunk2: remainder=%d, capacity=%d\n",
                   remainder, capacity_);
       memcpy(samples + space_to_end, &buffer_[0], remainder * sizeof(float));
@@ -169,7 +169,7 @@ void AudioRingBuffer::commit_write(int num_samples) {
   const int write = write_pos_.load(std::memory_order_acquire);
 
   // BOUNDS CHECK
-  FATAL_CHECK(write < 0 || write + num_samples > capacity_,
+  FATAL_CHECK(write >= 0 && write + num_samples <= capacity_,
               "commit_write out of bounds: write=%d, num_samples=%d, "
               "capacity=%d\n",
               write, num_samples, capacity_);
diff --git a/src/audio/tracker.cc b/src/audio/tracker.cc
index 38c814d..e7da26a 100644
--- a/src/audio/tracker.cc
+++ b/src/audio/tracker.cc
@@ -149,7 +149,7 @@ void tracker_init() {
   for (uint32_t pid = 0; pid < g_tracker_patterns_count; ++pid) {
     const TrackerPattern& pattern = g_tracker_patterns[pid];
     for (uint32_t i = 1; i < pattern.num_events; ++i) {
-      FATAL_CHECK(pattern.events[i].unit_time < pattern.events[i - 1].unit_time,
+      FATAL_CHECK(pattern.events[i].unit_time >= pattern.events[i - 1].unit_time,
                   "Pattern %d has unsorted events: event[%d].time=%.3f < "
                   "event[%d].time=%.3f\n",
                   pid, i, pattern.events[i].unit_time, i - 1,
diff --git a/src/gpu/effect_v2.cc b/src/gpu/effect_v2.cc
index 79a14b4..7ecdfbd 100644
--- a/src/gpu/effect_v2.cc
+++ b/src/gpu/effect_v2.cc
@@ -6,6 +6,6 @@
 EffectV2::EffectV2(const GpuContext& ctx, const std::vector<std::string>& inputs,
                    const std::vector<std::string>& outputs)
     : ctx_(ctx), input_nodes_(inputs), output_nodes_(outputs) {
-  FATAL_CHECK(inputs.empty(), "Effect must have at least one input\n");
-  FATAL_CHECK(outputs.empty(), "Effect must have at least one output\n");
+  FATAL_CHECK(!inputs.empty(), "Effect must have at least one input\n");
+  FATAL_CHECK(!outputs.empty(), "Effect must have at least one output\n");
 }
diff --git a/src/gpu/sequence_v2.cc b/src/gpu/sequence_v2.cc
index 9e30db0..7c44085 100644
--- a/src/gpu/sequence_v2.cc
+++ b/src/gpu/sequence_v2.cc
@@ -38,7 +38,7 @@ NodeRegistry::~NodeRegistry() {
 
 void NodeRegistry::declare_node(const std::string& name, NodeType type,
                                  int width, int height) {
-  FATAL_CHECK(nodes_.find(name) != nodes_.end(),
+  FATAL_CHECK(nodes_.find(name) == nodes_.end(),
               "Node already declared: %s\n", name.c_str());
 
   if (width <= 0)
@@ -57,9 +57,9 @@ void NodeRegistry::declare_node(const std::string& name, NodeType type,
 
 void NodeRegistry::declare_aliased_node(const std::string& name,
                                         const std::string& alias_of) {
-  FATAL_CHECK(nodes_.find(alias_of) == nodes_.end(),
+  FATAL_CHECK(nodes_.find(alias_of) != nodes_.end(),
               "Alias target does not exist: %s\n", alias_of.c_str());
-  FATAL_CHECK(aliases_.find(name) != aliases_.end(), "Alias already exists: %s\n",
+  FATAL_CHECK(aliases_.find(name) == aliases_.end(), "Alias already exists: %s\n",
               name.c_str());
 
   aliases_[name] = alias_of;
@@ -73,7 +73,7 @@ WGPUTextureView NodeRegistry::get_view(const std::string& name) {
   }
 
   auto it = nodes_.find(name);
-  FATAL_CHECK(it == nodes_.end(), "Node not found: %s\n", name.c_str());
+  FATAL_CHECK(it != nodes_.end(), "Node not found: %s\n", name.c_str());
   return it->second.view;
 }
 
@@ -161,7 +161,7 @@ void NodeRegistry::create_texture(Node& node) {
   desc.sampleCount = 1;
 
   node.texture = wgpuDeviceCreateTexture(device_, &desc);
-  FATAL_CHECK(node.texture == nullptr, "Failed to create texture\n");
+  FATAL_CHECK(node.texture != nullptr, "Failed to create texture\n");
 
   WGPUTextureViewDescriptor view_desc = {};
   view_desc.format = format;
@@ -175,7 +175,7 @@ void NodeRegistry::create_texture(Node& node) {
                          : WGPUTextureAspect_All;
 
   node.view = wgpuTextureCreateView(node.texture, &view_desc);
-  FATAL_CHECK(node.view == nullptr, "Failed to create texture view\n");
+  FATAL_CHECK(node.view != nullptr, "Failed to create texture view\n");
 }
 
 // SequenceV2 implementation
diff --git a/src/util/check_return.h b/src/util/check_return.h
index 89ed4bc..bfdadf5 100644
--- a/src/util/check_return.h
+++ b/src/util/check_return.h
@@ -138,7 +138,7 @@
 //   - Programming errors (assertion failures, invariant violations)
 //   - Corrupted state that cannot be recovered
 //   - Internal consistency checks
-//   - Example: FATAL_CHECK(idx >= size, "Index out of bounds: %d >= %d", idx,
+//   - Example: FATAL_CHECK(idx < size, "Index out of bounds: %d >= %d", idx,
 //   size)
 //
 // Use CHECK_RETURN for:
diff --git a/src/util/fatal_error.h b/src/util/fatal_error.h
index aaeba26..c0f7c65 100644
--- a/src/util/fatal_error.h
+++ b/src/util/fatal_error.h
@@ -43,9 +43,9 @@
 // ==============================================================================
 
 // Conditional fatal error check with formatted message
-// Usage: FATAL_CHECK(x >= max, "x out of bounds: %d >= %d\n", x, max);
+// Usage: FATAL_CHECK(x < max, "x out of bounds: %d >= %d\n", x, max);
 //
-// If condition is TRUE (error detected):
+// If condition is FALSE (assertion failed):
 //   - Prints "FATAL: <message> [file.cc:line]" to stderr
 //   - Calls abort()
 //
@@ -54,7 +54,7 @@
 //   [ring_buffer.cc:57]
 #define FATAL_CHECK(cond, ...)                                                 \
   do {                                                                         \
-    if (cond) {                                                                \
+    if (!(cond)) {                                                             \
       fprintf(stderr, "FATAL: " __VA_ARGS__);                                  \
       fprintf(stderr, " [%s:%d]\n", __FILE__, __LINE__);                       \
       abort();                                                                 \
@@ -126,9 +126,9 @@
 //
 // FATAL_CHECK(cond, msg, ...):
 //   - Most common use case (90% of error checks)
-//   - Bounds checking: FATAL_CHECK(idx >= size, "Index %d >= %d\n", idx, size)
-//   - Null checking: FATAL_CHECK(ptr == nullptr, "Null pointer: %s\n", name)
-//   - Range validation: FATAL_CHECK(x < min || x > max, "Out of range\n")
+//   - Bounds checking: FATAL_CHECK(idx < size, "Index %d >= %d\n", idx, size)
+//   - Null checking: FATAL_CHECK(ptr != nullptr, "Null pointer: %s\n", name)
+//   - Range validation: FATAL_CHECK(x >= min && x <= max, "Out of range\n")
 //
 // FATAL_ERROR(msg, ...):
 //   - Unconditional errors (should-never-happen cases)