use fvm instead of flutter package

PKGBUILD

@@ -24,9 +24,7 @@ depends=(
 # it again. The binary is able to run on glibc malloc, hence no mimalloc dependency here.
 makedepends=(
 	'git'
-	'flutter'
-	'flutter-target-linux'
-	'flutter-target-web'  # embedded web remote UI; the build script skips it when absent
+	'fvm'                 # upstream pins its Flutter SDK in .fvmrc, and the repos ship no flutter
 	'rustup'              # cargokit hard-requires `rustup run <toolchain> cargo build`
 	'java-environment'    # the jni plugin's linux CMake needs the JNI headers
 	'clang'
@@ -71,21 +69,31 @@ prepare() {
 		-e 's|^Icon=.*|Icon=io.github.MCDFSteve.NipaPlay-Reload|' \
 		assets/linux/io.github.MCDFSteve.NipaPlay-Reload.desktop
 
-	flutter pub get
+	# Fetch the Flutter SDK pinned in .fvmrc. Keep fvm's cache inside $srcdir instead
+	# of the builder's home, and skip the local git mirror -- it only pays off when
+	# juggling several SDK versions, and here it would just be a few hundred MB extra.
+	export FVM_CACHE_PATH="${srcdir}/fvm"
+	export FVM_USE_GIT_CACHE=false
+	fvm install
+
+	fvm flutter pub get
 }
 
 build() {
 	cd "${pkgname}"
 
+	export FVM_CACHE_PATH="${srcdir}/fvm"
+	export FVM_USE_GIT_CACHE=false
 	export FLUTTER_SUPPRESS_ANALYTICS=true
 	# Match upstream CI: fvp takes its deps from the latest mdk-sdk release
 	export FVP_DEPS_URL='https://github.com/wang-bin/mdk-sdk/releases/latest/download/'
 	export FVP_DEPS_LATEST=1
 
-	# Build the embedded web remote UI into assets/web/ (the script degrades on failure)
-	bash build_and_copy_web.sh
+	# Build the embedded web remote UI into assets/web/ (the script degrades on failure).
+	# It invokes a bare `flutter`, so it needs the pinned SDK on PATH.
+	fvm exec bash build_and_copy_web.sh
 
-	flutter build linux --release
+	fvm flutter build linux --release
 }
 
 package() {