diff --git a/src/discover/discover.c b/src/discover/discover.c
index 314c00c5..31b15baa 100644
--- a/src/discover/discover.c
+++ b/src/discover/discover.c
@@ -131,6 +131,32 @@ static bool str_contains(const char *s, const char *sub) {
     return strstr(s, sub) != NULL;
 }
 
+/* Windows IDE auto-index integrations can accidentally pass the IDE install
+ * directory itself as the repository root. These are not source projects and
+ * are mostly binary/runtime assets. Match on the normalized full path because
+ * cbm_should_skip_dir() only sees basenames during the walk. */
+static bool looks_like_ide_install_root(const char *path) {
+    if (!path) {
+        return false;
+    }
+
+    char normalized[CBM_SZ_4K];
+    size_t i = 0;
+    for (; path[i] && i + 1 < sizeof(normalized); i++) {
+        char c = path[i];
+        if (c == '\\') {
+            c = '/';
+        }
+        if (c >= 'A' && c <= 'Z') {
+            c = (char)(c - 'A' + 'a');
+        }
+        normalized[i] = c;
+    }
+    normalized[i] = '\0';
+
+    return strstr(normalized, "appdata/local/programs/antigravity") != NULL;
+}
+
 /* ── Public filter functions ─────────────────────── */
 
 bool cbm_should_skip_dir(const char *dirname, cbm_index_mode_t mode) {
@@ -541,6 +567,10 @@ int cbm_discover_ex(const char *repo_path, const cbm_discover_opts_t *opts, cbm_
         return CBM_NOT_FOUND;
     }
 
+    if (looks_like_ide_install_root(repo_path)) {
+        return 0;
+    }
+
     /* Load gitignore if .git directory exists */
     cbm_gitignore_t *gitignore = NULL;
     char gi_path[CBM_SZ_4K];
diff --git a/tests/test_discover.c b/tests/test_discover.c
index af51a928..69ed4ff3 100644
--- a/tests/test_discover.c
+++ b/tests/test_discover.c
@@ -309,6 +309,29 @@ TEST(discover_skips_git_dir) {
     PASS();
 }
 
+TEST(discover_skips_antigravity_install_root_issue403) {
+    char *base = th_mktempdir("cbm_disc_ide403");
+    ASSERT(base != NULL);
+
+    char ide_root[512];
+    snprintf(ide_root, sizeof(ide_root), "%s/AppData/Local/Programs/Antigravity IDE", base);
+    th_mkdir_p(ide_root);
+    th_write_file(TH_PATH(ide_root, "resources/app/main.js"), "console.log('ide runtime');\n");
+    th_write_file(TH_PATH(ide_root, "resources/app/package.json"), "{\"name\":\"antigravity\"}\n");
+
+    cbm_discover_opts_t opts = {0};
+    cbm_file_info_t *files = NULL;
+    int count = 0;
+
+    int rc = cbm_discover(ide_root, &opts, &files, &count);
+    ASSERT_EQ(rc, 0);
+    ASSERT_EQ(count, 0);
+
+    cbm_discover_free(files, count);
+    th_cleanup(base);
+    PASS();
+}
+
 TEST(discover_with_gitignore) {
     char *base = th_mktempdir("cbm_disc_gi");
     ASSERT(base != NULL);
@@ -777,6 +800,7 @@ SUITE(discover) {
     /* Integration tests (cross-platform) */
     RUN_TEST(discover_simple);
     RUN_TEST(discover_skips_git_dir);
+    RUN_TEST(discover_skips_antigravity_install_root_issue403);
     RUN_TEST(discover_with_gitignore);
     RUN_TEST(discover_gitignore_dir_excluded_issue234);
     RUN_TEST(discover_max_file_size);