refactor(cpp/core): file_watcher usa file_poll_diff

cpp/functions/core/file_watcher.cpp

@@ -1,5 +1,7 @@
 #include "file_watcher.h"
 
+#include "core/file_poll_diff.h"
+
 #include <cstring>
 #include <unordered_map>
 #include <vector>
@@ -280,4 +282,29 @@ const char*  file_watcher_last_error(const FileWatcher* w) { return w ? w->last_
 
 #endif
 
+// ─────────────────────────────────────────────────────────────────────────────
+// Helper portable basado en file_poll_diff (puro). Comun a todas las plataformas.
+// ─────────────────────────────────────────────────────────────────────────────
+
+std::vector<FileEvent> file_watcher_events_from_diff(
+    const std::vector<FileSnapshotEntry>& before,
+    const std::vector<FileSnapshotEntry>& after) {
+
+    // Convertir a fn_ui::FileEntry para llamar a la funcion pura.
+    std::vector<fn_ui::FileEntry> a, b;
+    a.reserve(before.size());
+    b.reserve(after.size());
+    for (const auto& e : before) a.push_back({e.path, e.size, e.mtime});
+    for (const auto& e : after)  b.push_back({e.path, e.size, e.mtime});
+
+    fn_ui::FileDiff diff = fn_ui::file_poll_diff(a, b);
+
+    std::vector<FileEvent> out;
+    out.reserve(diff.added.size() + diff.modified.size() + diff.removed.size());
+    for (const auto& p : diff.added)    out.push_back({p, FileEvent::Created});
+    for (const auto& p : diff.modified) out.push_back({p, FileEvent::Modified});
+    for (const auto& p : diff.removed)  out.push_back({p, FileEvent::Deleted});
+    return out;
+}
+
 } // namespace fn

cpp/functions/core/file_watcher.h

@@ -7,7 +7,12 @@
 // Otros:   stub (poll() devuelve siempre vacio)
 //
 // API no bloqueante: poll() drena los eventos disponibles desde la ultima llamada.
+//
+// Para plataformas sin backend nativo, el caller puede usar la helper
+// file_watcher_events_from_diff que delega en `file_poll_diff` (puro) para
+// derivar FileEvents a partir de dos snapshots tomados con stat()/opendir().
 
+#include <cstdint>
 #include <string>
 #include <vector>
 
@@ -21,6 +26,14 @@ struct FileEvent {
     Kind        kind;
 };
 
+// Snapshot de filesystem (forma simple, identica al fn_ui::FileEntry de
+// file_poll_diff_cpp_core). Se replica aqui para no acoplar headers en apps.
+struct FileSnapshotEntry {
+    std::string path;
+    uint64_t    size  = 0;
+    int64_t     mtime = 0;
+};
+
 // Crea un watcher vacio. El caller llama destroy.
 FileWatcher* file_watcher_create();
 
@@ -38,4 +51,14 @@ std::vector<FileEvent> file_watcher_poll(FileWatcher* w);
 // Devuelve el mensaje del ultimo error (vacio si no hay).
 const char* file_watcher_last_error(const FileWatcher* w);
 
+// Helper portable: convierte dos snapshots de FS en FileEvents usando la
+// logica pura `file_poll_diff_cpp_core`. Util en plataformas sin inotify/
+// RDCW o como fallback de polling. El caller construye los snapshots con
+// stat()/opendir().
+//
+// Mapeo: added -> Created, modified -> Modified, removed -> Deleted.
+std::vector<FileEvent> file_watcher_events_from_diff(
+    const std::vector<FileSnapshotEntry>& before,
+    const std::vector<FileSnapshotEntry>& after);
+
 } // namespace fn

cpp/functions/core/file_watcher.md

@@ -8,7 +8,7 @@ purity: impure
 signature: "fn::FileWatcher* fn::file_watcher_create(); void fn::file_watcher_destroy(fn::FileWatcher*); bool fn::file_watcher_add(fn::FileWatcher*, const char* path); std::vector<fn::FileEvent> fn::file_watcher_poll(fn::FileWatcher*); const char* fn::file_watcher_last_error(const fn::FileWatcher*)"
 description: "Watcher de archivos/directorios cross-platform (Linux inotify, Windows ReadDirectoryChangesW). API no bloqueante: registra paths con add() y consulta eventos con poll(). Cada poll() drena todos los eventos pendientes desde la llamada anterior."
 tags: [filesystem, watcher, inotify, file_events, io]
-uses_functions: []
+uses_functions: ["file_poll_diff_cpp_core"]
 uses_types: []
 returns: []
 returns_optional: false