feat(build): cache flet-build-template.zip; share FLET_CACHE_DIR with Gradle

CHANGELOG.md

@@ -5,6 +5,8 @@
 * Allow `[tool.flet.android.permission]` values to be TOML inline tables in addition to booleans — each `key = "value"` entry adds an `android:<key>="<value>"` attribute to the generated `<uses-permission>` element, unlocking modifiers like `android:maxSdkVersion` and `android:usesPermissionFlags` that real-world Android permissions (e.g. Bluetooth LE) require. The boolean form and the `--android-permissions` CLI flag are unchanged; a non-empty inline table is always emitted, an empty table (`{}`) is treated as `false`, and invalid value types fail the build with a clear error ([#6550](https://github.com/flet-dev/flet/issues/6550), [#6551](https://github.com/flet-dev/flet/pull/6551)) by @FeodorFitsner.
 * Upgrade the bundled Pyodide runtime in the `flet build web` template from `0.27.5` to `0.27.7` (includes `micropip` `0.9.0`) ([#6549](https://github.com/flet-dev/flet/pull/6549)) by @FeodorFitsner.
 * Drop generated `web/canvaskit/` build artifacts (`canvaskit.js`/`.wasm`/`.symbols` and the `chromium/` and `skwasm`/`skwasm_st` variants) from the `flet build web` template — these are produced by the Flutter web build and should not have been committed into the cookiecutter template ([#6549](https://github.com/flet-dev/flet/pull/6549)) by @FeodorFitsner.
+* Cache the downloaded `flet-build-template.zip` across builds. The build template is bound to an exact Flet version and is immutable, so on every `flet build` / `flet debug` after the first, the CLI now uses a previously-downloaded zip from `$FLET_CACHE_DIR/build-template/v<flet-version>/` (defaulting to `~/.flet/cache/build-template/v<flet-version>/`) instead of re-fetching it via cookiecutter. The CLI also exports `FLET_CACHE_DIR` into the child Gradle process, so `serious_python_android` >= 1.0.1 lands its Python dist tarballs (`python-android-dart-<py>-<abi>.tar.gz`) in the same cache root by default — fixing the multi-minute "Creating app shell" / `downloadDistArchive_*` delay on every Android debug build. Custom `--template` URLs and the local-dev template path are unchanged ([#6555](https://github.com/flet-dev/flet/discussions/6555), [#6558](https://github.com/flet-dev/flet/pull/6558)) by @FeodorFitsner.
+* Bump the bundled build template's `serious_python` dependency from `1.0.0` to `1.0.1` so Android builds pick up the new persistent Python-tarball cache + conditional-GET revalidation introduced in [`serious_python` 1.0.1](https://github.com/flet-dev/serious-python/blob/main/src/serious_python_android/CHANGELOG.md) ([#6558](https://github.com/flet-dev/flet/pull/6558)) by @FeodorFitsner.
 
 ### Bug fixes
 

sdk/python/packages/flet-cli/src/flet_cli/commands/build_base.py

@@ -1174,6 +1174,9 @@ def create_flutter_project(self, second_pass=False):
             template_ref = flet.version.flet_version
 
         is_local_dev = False
+        # Identity printed in status / hashed for invalidation; may differ from
+        # the path cookiecutter actually reads when caching kicks in below.
+        template_source = template_url
         if template_url:
             # User-provided template (git repo or local path) — use checkout
             checkout = template_ref
@@ -1182,13 +1185,19 @@ def create_flutter_project(self, second_pass=False):
             local_tpl = Path(__file__).resolve().parents[5] / "templates" / "build"
             if local_tpl.is_dir():
                 template_url = str(local_tpl)
+                template_source = template_url
                 checkout = None
                 is_local_dev = True
             else:
-                template_url = DEFAULT_TEMPLATE_URL.format(version=template_ref)
+                from flet_cli.utils.template_cache import get_cached_template_zip
+
+                template_source = DEFAULT_TEMPLATE_URL.format(version=template_ref)
+                template_url = str(
+                    get_cached_template_zip(template_source, template_ref)
+                )
                 checkout = None
 
-        hash.update(template_url)
+        hash.update(template_source)
         hash.update(template_ref)
 
         template_dir = self.options.template_dir or self.get_pyproject(
@@ -1214,7 +1223,7 @@ def create_flutter_project(self, second_pass=False):
             # create a new Flutter bootstrap project directory, if non-existent
             if not second_pass:
                 self.flutter_dir.mkdir(parents=True, exist_ok=True)
-                status = f"[bold blue]Creating app shell from {template_url}"
+                status = f"[bold blue]Creating app shell from {template_source}"
                 if checkout:
                     status += f' with ref "{template_ref}"'
                 status += "..."

sdk/python/packages/flet-cli/src/flet_cli/utils/template_cache.py

@@ -0,0 +1,48 @@
+import os
+import shutil
+import urllib.request
+from pathlib import Path
+
+
+def get_cache_root() -> Path:
+    """Resolve the Flet on-disk cache root.
+
+    Uses `$FLET_CACHE_DIR` if set, otherwise `~/.flet/cache`. The resolved
+    path is exported back into the process environment so child processes
+    (notably the Gradle build of `serious_python_android`) share the same
+    cache root by default.
+    """
+    root = os.environ.get("FLET_CACHE_DIR")
+    cache_root = Path(root).expanduser() if root else Path.home() / ".flet" / "cache"
+    os.environ["FLET_CACHE_DIR"] = str(cache_root)
+    return cache_root
+
+
+def get_cached_template_zip(url: str, version: str) -> Path:
+    """Return a local path to `flet-build-template.zip` for `version`.
+
+    The build template at a versioned release URL is immutable, so caching
+    is a simple "use if present, else download once" — no revalidation.
+    """
+    cache_path = (
+        get_cache_root() / "build-template" / f"v{version}" / "flet-build-template.zip"
+    )
+
+    if cache_path.exists() and cache_path.stat().st_size > 0:
+        return cache_path
+
+    cache_path.parent.mkdir(parents=True, exist_ok=True)
+    tmp_path = cache_path.with_suffix(cache_path.suffix + ".tmp")
+
+    try:
+        with urllib.request.urlopen(url) as resp, open(tmp_path, "wb") as out:
+            shutil.copyfileobj(resp, out)
+            out.flush()
+            os.fsync(out.fileno())
+        os.replace(tmp_path, cache_path)
+    except BaseException:
+        if tmp_path.exists():
+            tmp_path.unlink(missing_ok=True)
+        raise
+
+    return cache_path

sdk/python/templates/build/{{cookiecutter.out_dir}}/pubspec.yaml

@@ -17,7 +17,7 @@ dependencies:
 
   flet:
     path: ../../../../../packages/flet
-  serious_python: 1.0.0
+  serious_python: 1.0.1
 
   package_info_plus: ^9.0.0
   path_provider: ^2.1.4