gtauri: Tauri v2 gallery harness WORKING on emulator

Chromium owns scroll/compositor/lazy-load/image-cache; Rust owns
scan/SQLite/thumbnail-decode behind a gallery:// custom protocol.

Hard-won gotchas (see in-code comments):
- Android: no native custom-scheme support → wry rewrites the URL to
  http://gallery.localhost/... (custom_protocol_workaround). The JS
  MUST request that form; the handler receives the reverted
  gallery://localhost/... and must strip the authority.
- tauri_build::build() in build.rs must run UNCONDITIONALLY (build
  scripts run on the host: a cfg(target_os) gate silently disables it,
  which skips the rustc-cfg=mobile emission → no mobile_entry_point →
  .so with no JNI symbols → UnsatisfiedLinkError).
- build.rs must list frontend files for rerun-if-changed (a dir-level
  directive only watches the dir mtime, not content edits) — the .so
  bakes the frontend at compile time and cargo otherwise ships stale
  UI with a 'successful' build.
- logcat drops ~75% of lines under load: use the file trace.
- fetch() is CORS-restricted (page origin http://tauri.localhost);
  <img> is not — add ACAO:* anyway.

Emulator (5853 real files): grid renders, lazy thumbs via
gallery:// with on-disk cache (87 files 35-72KB), FR log clean at
60Hz, viewer opens full-res with compositor-only pan/zoom. The single
'broken' cell is a 17-byte fake test JPEG (correct behavior).

harnesses/gtauri/.tauriignore

@@ -0,0 +1 @@
+frontend/dist/img/

harnesses/gtauri/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "gtauri"
+version = "0.1.0"
+description = "gallery on Tauri"
+authors = ["gmp"]
+edition = "2021"
+
+[lib]
+name = "gtauri_lib"
+crate-type = ["staticlib", "cdylib", "rlib"]
+
+[build-dependencies]
+tauri-build = { version = "2", features = [] }
+
+[dependencies]
+tauri = { version = "2", features = [] }
+tauri-runtime-wry = "2"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+log = { version = "0.4", features = ["std"] }
+http = "1"
+# gallery engine (shared with the egui build):
+rusqlite = { version = "0.41", features = ["bundled"] }
+turbojpeg = { version = "1.5.1", features = ["cmake"] }
+kamadak-exif = "0.6"
+sha1 = "0.11"
+image = { version = "0.25", default-features = false, features = ["png"] }

harnesses/gtauri/build.rs

@@ -0,0 +1,27 @@
+// tauri::generate_context!() embeds `frontendDist` at compile time. Without
+// rerun directives cargo does NOT rebuild the .so when frontend files change
+// (observed: stale grid code survived a "successful" rebuild). Directory-level
+// rerun-if-changed only tracks the dir mtime (add/remove/rename, NOT content
+// edits), so list every file explicitly.
+fn walk(p: &std::path::Path) {
+    for e in std::fs::read_dir(p).unwrap() {
+        let e = e.unwrap();
+        let path = e.path();
+        if path.is_dir() {
+            walk(&path);
+        } else {
+            println!("cargo:rerun-if-changed={}", path.display());
+        }
+    }
+}
+
+fn main() {
+    walk(std::path::Path::new("frontend/dist"));
+    println!("cargo:rerun-if-changed=tauri.conf.json");
+
+    // tauri_build::build() inspects the TARGET env var itself (build scripts
+    // run on the HOST, so a cfg(target_os) gate would disable it). For
+    // android targets it emits `cargo:rustc-cfg=mobile`, which is what
+    // activates `#[cfg_attr(mobile, tauri::mobile_entry_point)]`.
+    tauri_build::build();
+}

harnesses/gtauri/capabilities/default.json

@@ -0,0 +1,11 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "default",
+  "description": "tttest: FR batching + lifecycle logs from the webview",
+  "windows": [
+    "main"
+  ],
+  "permissions": [
+    "core:default"
+  ]
+}