diff --git a/include/sm_scan_tree.h b/include/sm_scan_tree.h
new file mode 100644
index 0000000..3227b3f
--- /dev/null
+++ b/include/sm_scan_tree.h
@@ -0,0 +1,31 @@
+#ifndef SM_SCAN_TREE_H
+#define SM_SCAN_TREE_H
+
+#include <stdbool.h>
+
+typedef enum {
+  SM_SCAN_TREE_DIR_DESCEND = 0,
+  SM_SCAN_TREE_DIR_SKIP_DESCEND,
+  SM_SCAN_TREE_DIR_ABORT,
+} sm_scan_tree_dir_visit_t;
+
+typedef sm_scan_tree_dir_visit_t (*sm_scan_tree_dir_fn)(const char *dir_path,
+                                                        unsigned int depth_from_root,
+                                                        void *ctx);
+typedef bool (*sm_scan_tree_image_fn)(const char *image_path,
+                                      const char *image_name,
+                                      unsigned int depth_from_root,
+                                      void *ctx);
+
+typedef struct {
+  sm_scan_tree_dir_fn on_directory;
+  sm_scan_tree_image_fn on_image_file;
+} sm_scan_tree_callbacks_t;
+
+// Walk a managed scan subtree using the shared scan-depth and path filtering rules.
+bool sm_scan_tree_walk(const char *scan_root, const char *dir_path,
+                       unsigned int depth_from_root,
+                       unsigned int remaining_depth,
+                       const sm_scan_tree_callbacks_t *callbacks, void *ctx);
+
+#endif
diff --git a/src/sm_scan.c b/src/sm_scan.c
index 26ec036..5226bc7 100644
--- a/src/sm_scan.c
+++ b/src/sm_scan.c
@@ -1,6 +1,7 @@
 #include "sm_platform.h"
 #include "sm_runtime.h"
 #include "sm_scan.h"
+#include "sm_scan_tree.h"
 #include "sm_types.h"
 #include "sm_game_cache.h"
 #include "sm_gameinfo.h"
@@ -31,43 +32,6 @@ static bool is_under_discovered_param_root(
   return false;
 }
 
-static void classify_scan_entry(const char *full_path, unsigned char d_type,
-                                bool *is_dir_out, bool *is_regular_out) {
-  bool is_dir = false;
-  bool is_regular = false;
-
-  if (d_type == DT_DIR) {
-    is_dir = true;
-  } else if (d_type == DT_REG) {
-    is_regular = true;
-  } else if (d_type == DT_UNKNOWN) {
-    struct stat st;
-    if (lstat(full_path, &st) == 0) {
-      is_dir = S_ISDIR(st.st_mode);
-      is_regular = S_ISREG(st.st_mode);
-    }
-  }
-
-  if (is_dir_out)
-    *is_dir_out = is_dir;
-  if (is_regular_out)
-    *is_regular_out = is_regular;
-}
-
-static bool is_distinct_configured_scan_root(const char *current_scan_root,
-                                             const char *path) {
-  for (int i = 0; i < get_scan_path_count(); i++) {
-    const char *scan_path = get_scan_path(i);
-    if (strcmp(scan_path, path) != 0)
-      continue;
-    if (current_scan_root && strcmp(current_scan_root, path) == 0)
-      return false;
-    return true;
-  }
-
-  return false;
-}
-
 // --- Candidate Discovery ---
 static bool try_collect_candidate_for_directory(
     const char *full_path, scan_candidate_t *candidates, int max_candidates,
@@ -200,65 +164,43 @@ static bool try_collect_candidate_for_directory(
   return true;
 }
 
-static void collect_candidates_with_depth(
-    const char *current_scan_root, const char *dir_path,
-    unsigned int remaining_depth, scan_candidate_t *candidates,
-    int max_candidates, int *candidate_count,
-    const struct AppDbTitleList *app_db_titles, bool app_db_titles_ready,
-    char discovered_param_roots[][MAX_PATH],
-    int *discovered_param_root_count, bool *unstable_found_out) {
-  if (should_stop_requested())
-    return;
+typedef struct {
+  scan_candidate_t *candidates;
+  int max_candidates;
+  int *candidate_count;
+  const struct AppDbTitleList *app_db_titles;
+  bool app_db_titles_ready;
+  char (*discovered_param_roots)[MAX_PATH];
+  int *discovered_param_root_count;
+  bool *unstable_found_out;
+} collect_candidates_walk_ctx_t;
 
-  if (is_distinct_configured_scan_root(current_scan_root, dir_path))
-    return;
+static sm_scan_tree_dir_visit_t collect_candidate_directory_visit(
+    const char *dir_path, unsigned int depth_from_root, void *ctx_ptr) {
+  if (depth_from_root == 0u)
+    return SM_SCAN_TREE_DIR_DESCEND;
 
-  // Once a directory has sce_sys/param.json (valid or not),
-  // it is treated as a terminal game root and descendants are skipped.
+  collect_candidates_walk_ctx_t *ctx = (collect_candidates_walk_ctx_t *)ctx_ptr;
   if (try_collect_candidate_for_directory(
-          dir_path, candidates, max_candidates, candidate_count, app_db_titles,
-          app_db_titles_ready, discovered_param_roots,
-          discovered_param_root_count, unstable_found_out)) {
-    return;
+          dir_path, ctx->candidates, ctx->max_candidates, ctx->candidate_count,
+          ctx->app_db_titles, ctx->app_db_titles_ready,
+          ctx->discovered_param_roots, ctx->discovered_param_root_count,
+          ctx->unstable_found_out)) {
+    return SM_SCAN_TREE_DIR_SKIP_DESCEND;
   }
 
-  if (remaining_depth == 0)
-    return;
+  return SM_SCAN_TREE_DIR_DESCEND;
+}
 
-  DIR *d = opendir(dir_path);
-  if (!d)
-    return;
+static bool collect_candidate_image_visit(const char *image_path,
+                                          const char *image_name,
+                                          unsigned int depth_from_root,
+                                          void *ctx_ptr) {
+  (void)depth_from_root;
 
-  struct dirent *entry;
-  while ((entry = readdir(d)) != NULL) {
-    if (should_stop_requested())
-      break;
-    if (entry->d_name[0] == '.')
-      continue;
-
-    char full_path[MAX_PATH];
-    snprintf(full_path, sizeof(full_path), "%s/%s", dir_path, entry->d_name);
-
-    bool is_dir = false;
-    bool is_regular = false;
-    classify_scan_entry(full_path, entry->d_type, &is_dir, &is_regular);
-
-    if (!path_matches_root_or_child(current_scan_root, IMAGE_MOUNT_BASE) &&
-        is_regular && is_supported_image_file_name(entry->d_name)) {
-      maybe_mount_image_file(full_path, entry->d_name, unstable_found_out);
-    }
-
-    if (!is_dir)
-      continue;
-
-    collect_candidates_with_depth(
-        current_scan_root, full_path, remaining_depth - 1u, candidates,
-        max_candidates, candidate_count, app_db_titles, app_db_titles_ready,
-        discovered_param_roots, discovered_param_root_count,
-        unstable_found_out);
-  }
-
-  closedir(d);
+  collect_candidates_walk_ctx_t *ctx = (collect_candidates_walk_ctx_t *)ctx_ptr;
+  maybe_mount_image_file(image_path, image_name, ctx->unstable_found_out);
+  return true;
 }
 
 static bool build_backport_mount_context(const char *title_id,
@@ -366,47 +308,24 @@ static void collect_scan_candidates_from_root(
     return;
 
   unsigned int scan_depth = runtime_config()->scan_depth;
-  bool has_backports_root = !is_under_image_mount_base(scan_path);
-
   if (scan_depth < MIN_SCAN_DEPTH)
     scan_depth = MIN_SCAN_DEPTH;
 
-  DIR *d = opendir(scan_path);
-  if (!d)
-    return;
-
-  struct dirent *entry;
-  while ((entry = readdir(d)) != NULL) {
-    if (should_stop_requested())
-      break;
-    if (entry->d_name[0] == '.')
-      continue;
-    if (has_backports_root &&
-        strcmp(entry->d_name, DEFAULT_BACKPORTS_DIR_NAME) == 0) {
-      continue;
-    }
-
-    char full_path[MAX_PATH];
-    snprintf(full_path, sizeof(full_path), "%s/%s", scan_path, entry->d_name);
-
-    bool is_dir = false;
-    bool is_regular = false;
-    classify_scan_entry(full_path, entry->d_type, &is_dir, &is_regular);
-
-    if (!path_matches_root_or_child(scan_path, IMAGE_MOUNT_BASE) && is_regular &&
-        is_supported_image_file_name(entry->d_name))
-      maybe_mount_image_file(full_path, entry->d_name, unstable_found_out);
-    if (!is_dir)
-      continue;
-
-    collect_candidates_with_depth(
-        scan_path, full_path, scan_depth - 1u, candidates, max_candidates,
-        candidate_count, app_db_titles, app_db_titles_ready,
-        discovered_param_roots, discovered_param_root_count,
-        unstable_found_out);
-  }
-
-  closedir(d);
+  collect_candidates_walk_ctx_t ctx = {
+      .candidates = candidates,
+      .max_candidates = max_candidates,
+      .candidate_count = candidate_count,
+      .app_db_titles = app_db_titles,
+      .app_db_titles_ready = app_db_titles_ready,
+      .discovered_param_roots = discovered_param_roots,
+      .discovered_param_root_count = discovered_param_root_count,
+      .unstable_found_out = unstable_found_out,
+  };
+  sm_scan_tree_callbacks_t callbacks = {
+      .on_directory = collect_candidate_directory_visit,
+      .on_image_file = collect_candidate_image_visit,
+  };
+  (void)sm_scan_tree_walk(scan_path, scan_path, 0u, scan_depth, &callbacks, &ctx);
 }
 
 int collect_scan_candidates_for_scan_root(const char *scan_root,
diff --git a/src/sm_scan_tree.c b/src/sm_scan_tree.c
new file mode 100644
index 0000000..162f266
--- /dev/null
+++ b/src/sm_scan_tree.c
@@ -0,0 +1,121 @@
+#include "sm_platform.h"
+#include "sm_scan_tree.h"
+
+#include "sm_config_mount.h"
+#include "sm_filesystem.h"
+#include "sm_image.h"
+#include "sm_path_utils.h"
+#include "sm_paths.h"
+#include "sm_runtime.h"
+
+static void classify_scan_tree_entry(const char *full_path, unsigned char d_type,
+                                     bool *is_dir_out, bool *is_regular_out) {
+  bool is_dir = false;
+  bool is_regular = false;
+
+  if (d_type == DT_DIR) {
+    is_dir = true;
+  } else if (d_type == DT_REG) {
+    is_regular = true;
+  } else if (d_type == DT_UNKNOWN) {
+    struct stat st;
+    if (lstat(full_path, &st) == 0) {
+      is_dir = S_ISDIR(st.st_mode);
+      is_regular = S_ISREG(st.st_mode);
+    }
+  }
+
+  *is_dir_out = is_dir;
+  *is_regular_out = is_regular;
+}
+
+static bool is_distinct_configured_scan_root(const char *current_scan_root,
+                                             const char *path) {
+  for (int i = 0; i < get_scan_path_count(); i++) {
+    const char *scan_path = get_scan_path(i);
+    if (strcmp(scan_path, path) != 0)
+      continue;
+    if (strcmp(current_scan_root, path) == 0)
+      return false;
+    return true;
+  }
+
+  return false;
+}
+
+bool sm_scan_tree_walk(const char *scan_root, const char *dir_path,
+                       unsigned int depth_from_root,
+                       unsigned int remaining_depth,
+                       const sm_scan_tree_callbacks_t *callbacks, void *ctx) {
+  if (should_stop_requested())
+    return true;
+
+  if (depth_from_root > 0u &&
+      is_distinct_configured_scan_root(scan_root, dir_path)) {
+    return true;
+  }
+
+  sm_scan_tree_dir_visit_t dir_visit = SM_SCAN_TREE_DIR_DESCEND;
+  if (callbacks->on_directory) {
+    dir_visit = callbacks->on_directory(dir_path, depth_from_root, ctx);
+    if (dir_visit == SM_SCAN_TREE_DIR_ABORT)
+      return false;
+    if (dir_visit == SM_SCAN_TREE_DIR_SKIP_DESCEND)
+      return true;
+  }
+
+  if (remaining_depth == 0u)
+    return true;
+
+  DIR *d = opendir(dir_path);
+  if (!d)
+    return true;
+
+  bool skip_backports_root =
+      (depth_from_root == 0u && !is_under_image_mount_base(scan_root));
+  bool allow_image_file_visits =
+      callbacks->on_image_file &&
+      !path_matches_root_or_child(scan_root, IMAGE_MOUNT_BASE);
+
+  struct dirent *entry;
+  while ((entry = readdir(d)) != NULL) {
+    if (should_stop_requested()) {
+      closedir(d);
+      return true;
+    }
+    if (entry->d_name[0] == '.')
+      continue;
+    if (skip_backports_root &&
+        strcmp(entry->d_name, DEFAULT_BACKPORTS_DIR_NAME) == 0) {
+      continue;
+    }
+
+    char full_path[MAX_PATH];
+    snprintf(full_path, sizeof(full_path), "%s/%s", dir_path, entry->d_name);
+
+    bool is_dir = false;
+    bool is_regular = false;
+    classify_scan_tree_entry(full_path, entry->d_type, &is_dir, &is_regular);
+
+    if (allow_image_file_visits && is_regular &&
+        is_supported_image_file_name(entry->d_name)) {
+      if (!callbacks->on_image_file(full_path, entry->d_name, depth_from_root + 1u,
+                                    ctx)) {
+        closedir(d);
+        return false;
+      }
+    }
+
+    if (!is_dir)
+      continue;
+
+    if (!sm_scan_tree_walk(scan_root, full_path, depth_from_root + 1u,
+                           remaining_depth - 1u, callbacks, ctx)) {
+      closedir(d);
+      return false;
+    }
+  }
+
+  closedir(d);
+  return true;
+}
diff --git a/src/sm_scanner.c b/src/sm_scanner.c
index 112f8a4..e2909dd 100644
--- a/src/sm_scanner.c
+++ b/src/sm_scanner.c
@@ -14,6 +14,7 @@
 #include "sm_paths.h"
 #include "sm_runtime.h"
 #include "sm_scan.h"
+#include "sm_scan_tree.h"
 #include "sm_scanner.h"
 #include "sm_time.h"
 #include "sm_types.h"
@@ -225,41 +226,6 @@ static bool rebuild_scanner_watch_fd_index(void) {
   return rebuild_scanner_watch_fd_index_with_count(g_scanner_watch_count);
 }
 
-static bool is_distinct_configured_scan_root(const char *current_scan_root,
-                                             const char *path) {
-  for (int i = 0; i < get_scan_path_count(); i++) {
-    const char *scan_path = get_scan_path(i);
-    if (strcmp(scan_path, path) != 0)
-      continue;
-    if (current_scan_root && strcmp(current_scan_root, path) == 0)
-      return false;
-    return true;
-  }
-
-  return false;
-}
-
-static void classify_watch_entry(const char *full_path, unsigned char d_type,
-                                 bool *is_dir_out, bool *is_regular_out) {
-  bool is_dir = false;
-  bool is_regular = false;
-
-  if (d_type == DT_DIR) {
-    is_dir = true;
-  } else if (d_type == DT_REG) {
-    is_regular = true;
-  } else if (d_type == DT_UNKNOWN) {
-    struct stat st;
-    if (lstat(full_path, &st) == 0) {
-      is_dir = S_ISDIR(st.st_mode);
-      is_regular = S_ISREG(st.st_mode);
-    }
-  }
-
-  *is_dir_out = is_dir;
-  *is_regular_out = is_regular;
-}
-
 static void link_scanner_watch_entry_to_root(size_t index) {
   scanner_watch_entry_t *entry = &g_scanner_watch_entries[index];
   size_t head = g_scanner_root_watch_heads[entry->scan_root_index];
@@ -464,76 +430,35 @@ static bool resolve_watch_tree_rebuild_target(const scanner_watch_entry_t *entry
   }
 }
 
-static bool register_scan_dir_tree(int kq, int scan_root_index,
-                                   const char *current_scan_root,
-                                   const char *dir_path,
-                                   unsigned int depth_from_root,
-                                   unsigned int remaining_depth) {
-  if (depth_from_root > 0 &&
-      is_distinct_configured_scan_root(current_scan_root, dir_path)) {
-    return true;
-  }
+typedef struct {
+  int kq;
+  int scan_root_index;
+} register_watch_tree_ctx_t;
 
+static sm_scan_tree_dir_visit_t register_watch_directory_visit(
+    const char *dir_path, unsigned int depth_from_root, void *ctx_ptr) {
+  register_watch_tree_ctx_t *ctx = (register_watch_tree_ctx_t *)ctx_ptr;
   scanner_watch_kind_t kind =
       (depth_from_root == 0u) ? SCANNER_WATCH_SCAN_ROOT
                               : SCANNER_WATCH_SCAN_SUBDIR;
-  if (!register_scanner_watch_entry(kq, scan_root_index, dir_path, kind,
+  if (!register_scanner_watch_entry(ctx->kq, ctx->scan_root_index, dir_path, kind,
                                     (uint8_t)depth_from_root)) {
-    return false;
+    return SM_SCAN_TREE_DIR_ABORT;
   }
 
-  if (remaining_depth == 0u)
-    return true;
+  return SM_SCAN_TREE_DIR_DESCEND;
+}
 
-  DIR *d = opendir(dir_path);
-  if (!d)
-    return true;
+static bool register_watch_image_visit(const char *image_path,
+                                       const char *image_name,
+                                       unsigned int depth_from_root,
+                                       void *ctx_ptr) {
+  (void)image_name;
 
-  bool skip_backports_root =
-      (depth_from_root == 0u && !is_under_image_mount_base(current_scan_root));
-
-  struct dirent *entry;
-  while ((entry = readdir(d)) != NULL) {
-    if (should_stop_requested()) {
-      closedir(d);
-      return true;
-    }
-    if (entry->d_name[0] == '.')
-      continue;
-    if (skip_backports_root &&
-        strcmp(entry->d_name, DEFAULT_BACKPORTS_DIR_NAME) == 0) {
-      continue;
-    }
-
-    char full_path[MAX_PATH];
-    snprintf(full_path, sizeof(full_path), "%s/%s", dir_path, entry->d_name);
-
-    bool is_dir = false;
-    bool is_regular = false;
-    classify_watch_entry(full_path, entry->d_type, &is_dir, &is_regular);
-
-    if (!path_matches_root_or_child(current_scan_root, IMAGE_MOUNT_BASE) &&
-        is_regular && is_supported_image_file_name(entry->d_name)) {
-      if (!register_scanner_watch_entry(kq, scan_root_index, full_path,
-                                        SCANNER_WATCH_SCAN_IMAGE_FILE,
-                                        (uint8_t)(depth_from_root + 1u))) {
-        closedir(d);
-        return false;
-      }
-    }
-    if (!is_dir)
-      continue;
-
-    if (!register_scan_dir_tree(kq, scan_root_index, current_scan_root,
-                                full_path, depth_from_root + 1u,
-                                remaining_depth - 1u)) {
-      closedir(d);
-      return false;
-    }
-  }
-
-  closedir(d);
-  return true;
+  register_watch_tree_ctx_t *ctx = (register_watch_tree_ctx_t *)ctx_ptr;
+  return register_scanner_watch_entry(ctx->kq, ctx->scan_root_index, image_path,
+                                      SCANNER_WATCH_SCAN_IMAGE_FILE,
+                                      (uint8_t)depth_from_root);
 }
 
 static bool rebuild_scan_root_watch_tree(int kq, int scan_root_index) {
@@ -545,8 +470,16 @@ static bool rebuild_scan_root_watch_tree(int kq, int scan_root_index) {
   if (scan_depth < MIN_SCAN_DEPTH)
     scan_depth = MIN_SCAN_DEPTH;
 
-  if (!register_scan_dir_tree(kq, scan_root_index, scan_root, scan_root, 0u,
-                              scan_depth)) {
+  register_watch_tree_ctx_t walk_ctx = {
+      .kq = kq,
+      .scan_root_index = scan_root_index,
+  };
+  sm_scan_tree_callbacks_t callbacks = {
+      .on_directory = register_watch_directory_visit,
+      .on_image_file = register_watch_image_visit,
+  };
+  if (!sm_scan_tree_walk(scan_root, scan_root, 0u, scan_depth, &callbacks,
+                         &walk_ctx)) {
     return false;
   }
 
@@ -596,8 +529,16 @@ static bool rebuild_scan_root_watch_subtree(int kq, int scan_root_index,
     return true;
   }
 
-  if (!register_scan_dir_tree(kq, scan_root_index, scan_root, rebuild_path,
-                              rebuild_depth, scan_depth - rebuild_depth)) {
+  register_watch_tree_ctx_t walk_ctx = {
+      .kq = kq,
+      .scan_root_index = scan_root_index,
+  };
+  sm_scan_tree_callbacks_t callbacks = {
+      .on_directory = register_watch_directory_visit,
+      .on_image_file = register_watch_image_visit,
+  };
+  if (!sm_scan_tree_walk(scan_root, rebuild_path, rebuild_depth,
+                         scan_depth - rebuild_depth, &callbacks, &walk_ctx)) {
     return false;
   }