feat(cpp/core): añadir file_poll_diff pure

cpp/apps/primitives_gallery/CMakeLists.txt

@@ -17,9 +17,10 @@ add_imgui_app(primitives_gallery
     ${CMAKE_SOURCE_DIR}/functions/core/timeline.cpp
     demos_sql.cpp
     demos_scientific.cpp
-    # text_editor + file_watcher (issue 0025)
+    # text_editor + file_watcher (issue 0025) + file_poll_diff pure (issue 0045)
     ${CMAKE_SOURCE_DIR}/functions/core/text_editor.cpp
     ${CMAKE_SOURCE_DIR}/functions/core/file_watcher.cpp
+    ${CMAKE_SOURCE_DIR}/functions/core/file_poll_diff.cpp
     ${CMAKE_SOURCE_DIR}/vendor/imgui_text_edit/TextEditor.cpp
     # sql_workbench (issue 0032) + sql_parse pure (issue 0045)
     ${CMAKE_SOURCE_DIR}/functions/core/sql_workbench.cpp

cpp/apps/text_editor_smoke/CMakeLists.txt

@@ -7,6 +7,7 @@ add_imgui_app(text_editor_smoke
     main.cpp
     ${CMAKE_SOURCE_DIR}/functions/core/text_editor.cpp
     ${CMAKE_SOURCE_DIR}/functions/core/file_watcher.cpp
+    ${CMAKE_SOURCE_DIR}/functions/core/file_poll_diff.cpp
     ${CMAKE_SOURCE_DIR}/vendor/imgui_text_edit/TextEditor.cpp
 )
 target_include_directories(text_editor_smoke PRIVATE

cpp/functions/core/file_poll_diff.cpp

@@ -0,0 +1,45 @@
+#include "core/file_poll_diff.h"
+
+#include <unordered_map>
+#include <unordered_set>
+
+namespace fn_ui {
+
+FileDiff file_poll_diff(const std::vector<FileEntry>& before,
+                        const std::vector<FileEntry>& after) {
+    FileDiff out;
+
+    // Index before by path para lookup O(1).
+    std::unordered_map<std::string, const FileEntry*> idx_before;
+    idx_before.reserve(before.size());
+    for (const auto& e : before) {
+        idx_before[e.path] = &e;
+    }
+
+    // Recorrer after: clasificar added/modified.
+    std::unordered_set<std::string> seen_in_after;
+    seen_in_after.reserve(after.size());
+    for (const auto& e : after) {
+        seen_in_after.insert(e.path);
+        auto it = idx_before.find(e.path);
+        if (it == idx_before.end()) {
+            out.added.push_back(e.path);
+        } else {
+            const FileEntry* prev = it->second;
+            if (prev->size != e.size || prev->mtime != e.mtime) {
+                out.modified.push_back(e.path);
+            }
+        }
+    }
+
+    // Recorrer before: detectar removed (paths que no estan en after).
+    for (const auto& e : before) {
+        if (seen_in_after.find(e.path) == seen_in_after.end()) {
+            out.removed.push_back(e.path);
+        }
+    }
+
+    return out;
+}
+
+} // namespace fn_ui

cpp/functions/core/file_poll_diff.h

@@ -0,0 +1,34 @@
+#pragma once
+
+// file_poll_diff — diff puro entre dos snapshots de filesystem.
+//
+// Pareja natural de file_watcher: en plataformas sin inotify/RDCW (o cuando
+// se quiere fallback portable), el caller toma snapshots periodicos via
+// stat()/opendir() y los compara con esta funcion para emitir eventos
+// added/modified/removed. Sin I/O, sin estado.
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace fn_ui {
+
+struct FileEntry {
+    std::string path;
+    uint64_t    size  = 0;
+    int64_t     mtime = 0;  // unix seconds
+};
+
+struct FileDiff {
+    std::vector<std::string> added;
+    std::vector<std::string> modified;  // size o mtime distinto
+    std::vector<std::string> removed;
+};
+
+// Pura: calcula diff entre dos snapshots por path. Asume entries con paths
+// unicos en cada snapshot. Orden de los vectores: el orden en que aparecen
+// los paths en `after` (added/modified) y en `before` (removed).
+FileDiff file_poll_diff(const std::vector<FileEntry>& before,
+                        const std::vector<FileEntry>& after);
+
+} // namespace fn_ui

cpp/functions/core/file_poll_diff.md

@@ -0,0 +1,77 @@
+---
+name: file_poll_diff
+kind: function
+lang: cpp
+domain: core
+version: "1.0.0"
+purity: pure
+signature: "fn_ui::FileDiff fn_ui::file_poll_diff(const std::vector<fn_ui::FileEntry>& before, const std::vector<fn_ui::FileEntry>& after)"
+description: "Diff puro entre dos snapshots de filesystem (path/size/mtime). Devuelve vectores added/modified/removed. Sin I/O. Pareja del file_watcher para fallback portable basado en polling."
+tags: [filesystem, diff, poll, snapshot, pure]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: []
+tested: true
+tests: ["file_poll_diff detects added/modified/removed", "file_poll_diff: empty inputs", "file_poll_diff: identical snapshots"]
+test_file_path: "cpp/tests/test_file_poll_diff.cpp"
+file_path: "cpp/functions/core/file_poll_diff.cpp"
+params:
+  - name: before
+    desc: "Snapshot anterior. Vector de FileEntry {path, size, mtime}, paths unicos"
+  - name: after
+    desc: "Snapshot actual. Mismo formato. Paths unicos"
+output: "FileDiff con tres vectores de paths: added (en after y no en before), modified (path comun pero size o mtime distinto), removed (en before y no en after)."
+---
+
+# file_poll_diff
+
+Logica pura para calcular cambios de filesystem entre dos snapshots. Sin
+I/O, sin estado: el caller hace `stat()`/`opendir()` por su lado, construye
+los `FileEntry`, y esta funcion los compara.
+
+## API
+
+```cpp
+namespace fn_ui {
+
+struct FileEntry {
+    std::string path;
+    uint64_t    size  = 0;
+    int64_t     mtime = 0;  // unix seconds
+};
+
+struct FileDiff {
+    std::vector<std::string> added;
+    std::vector<std::string> modified;
+    std::vector<std::string> removed;
+};
+
+FileDiff file_poll_diff(const std::vector<FileEntry>& before,
+                        const std::vector<FileEntry>& after);
+
+}
+```
+
+## Reglas
+
+- Comparacion por `path` exacto.
+- "Modified": al menos uno de `size` o `mtime` cambia.
+- Asume paths unicos por snapshot (la funcion no deduplica).
+- Complejidad: O(N+M) con un `unordered_map<string, const FileEntry*>` para
+  indexar `before`.
+
+## Cuando usar
+
+- En plataformas donde `file_watcher` no tiene backend nativo (stub) y se
+  necesita un fallback basado en polling.
+- Para consolidar bursts de eventos: tomar dos snapshots en el tiempo y
+  reportar solo el cambio neto (sin los intermedios).
+- Tests del watcher: simular cambios de FS sin tocar disco.
+
+## Por que pura
+
+No abre archivos, no llama `stat`, no usa el reloj. Misma entrada produce la
+misma salida — testeable sin fixtures de FS.