feat: CV module — frame diff + threshold (blob tracking TODO)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

firmware/test/test_cv/test_cv.cpp

@@ -0,0 +1,70 @@
+// firmware/test/test_native/test_cv.cpp
+#include <unity.h>
+#include <string.h>
+#include "cv.h"
+
+static void fill_frame(uint8_t* f, uint8_t val) {
+    memset(f, val, CV_PIXELS);
+}
+
+void setUp(void) {}
+void tearDown(void) {}
+
+void test_frame_diff_no_change_gives_no_fg() {
+    CVState state;
+    cv_init(state);
+
+    uint8_t frame[CV_PIXELS];
+    fill_frame(frame, 128);
+
+    CVResult r1 = cv_process(state, frame, 50);
+    TEST_ASSERT_EQUAL_INT(0, r1.entries_delta);
+
+    CVResult r2 = cv_process(state, frame, 50);
+    TEST_ASSERT_EQUAL_INT(0, r2.entries_delta);
+    TEST_ASSERT_EQUAL_INT(0, r2.exits_delta);
+}
+
+void test_frame_diff_large_change_detected_no_crash() {
+    CVState state;
+    cv_init(state);
+
+    uint8_t bg[CV_PIXELS], fg_frame[CV_PIXELS];
+    fill_frame(bg, 100);
+    fill_frame(fg_frame, 200);
+
+    cv_process(state, bg, 50);
+    CVResult r = cv_process(state, fg_frame, 50);
+
+    // Tracking not yet implemented — just verify no crash and result is zero
+    TEST_ASSERT_EQUAL_INT(0, r.entries_delta);
+    TEST_ASSERT_EQUAL_INT(0, r.exits_delta);
+}
+
+void test_cv_init_clears_state() {
+    CVState state;
+    state.entries = 99; state.exits = 88;
+    cv_init(state);
+    TEST_ASSERT_EQUAL_INT(0, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
+    TEST_ASSERT_FALSE(state.bg_valid);
+}
+
+void test_cv_reset_counts() {
+    CVState state;
+    cv_init(state);
+    state.entries = 5;
+    state.exits   = 3;
+    cv_reset_counts(state);
+    TEST_ASSERT_EQUAL_INT(0, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
+}
+
+int main() {
+    UNITY_BEGIN();
+    RUN_TEST(test_frame_diff_no_change_gives_no_fg);
+    RUN_TEST(test_frame_diff_large_change_detected_no_crash);
+    RUN_TEST(test_cv_init_clears_state);
+    RUN_TEST(test_cv_reset_counts);
+    return UNITY_END();
+}