Require system .NET SDK; cache vpk/ffmpeg persistently

Per-build downloads of the dotnet runtime (~80 MB) were slow and flaky
(IncompleteRead killed a CI run). The .NET SDK is now a build-host
prerequisite; vpk and ffmpeg download once into a user-level cache
(~/.cache/mediahive-build, %LOCALAPPDATA%\mediahive-build) that
survives the per-run build dir.

scripts/MediaHive.spec

@@ -5,8 +5,9 @@
 #     pyinstaller --noconfirm --clean scripts/MediaHive.spec
 #
 # Or use the build script (recommended—handles versioning and packaging):
-#   uv run scripts/winbuild.py
+#   uv run scripts/guibuild.py
 
+import os
 import sys
 import mediahive.winmain
 import mediahive.server
@@ -20,7 +21,15 @@ _frontend_build = _pkg / "frontend-build"
 _logo_webp = _pkg / "assets" / "mediahive.webp"
 _icon_win = _pkg / "assets" / "mediahive.ico"
 _icon_mac = _pkg / "assets" / "mediahive.icns"
-_tools_dir = Path(SPECPATH).parent / "build" / "ffmpeg"
+# ffmpeg staging lives in the persistent build cache (same logic as
+# scripts/guibuild.py); fall back to the legacy build/ffmpeg location.
+if sys.platform == "win32":
+    _cache_base = Path(os.environ.get("LOCALAPPDATA", Path.home() / "AppData" / "Local"))
+else:
+    _cache_base = Path(os.environ.get("XDG_CACHE_HOME", Path.home() / ".cache"))
+_tools_dir = _cache_base / "mediahive-build" / "ffmpeg"
+if not _tools_dir.exists():
+    _tools_dir = Path(SPECPATH).parent / "build" / "ffmpeg"
 _tool_names = ["ffmpeg.exe"] if sys.platform == "win32" else ["ffmpeg"]
 
 _binaries = []

scripts/guibuild.py

@@ -2,7 +2,7 @@
 """Build the desktop GUI application and package it with Velopack.
 
 Usage:
-    uv run scripts/winbuild.py
+    uv run scripts/guibuild.py
 
 This runs in the project environment where dependencies
 are available via pyproject.toml.
@@ -26,7 +26,6 @@ import shutil
 import stat
 import subprocess
 import sys
-import tarfile
 import urllib.request
 import zipfile
 from pathlib import Path
@@ -41,10 +40,21 @@ _FFMPEG_URL = (
 _MACOS_ARM64_TOOL_URLS = {
     "ffmpeg": "https://www.osxexperts.net/ffmpeg81arm.zip",
 }
-_FFMPEG_STAGING = Path(__file__).parent.parent / "build" / "ffmpeg"
 _REPO_ROOT = Path(__file__).parent.parent
 _ASSETS_DIR = _REPO_ROOT / "mediahive" / "assets"
 
+
+def _build_cache_dir() -> Path:
+    """Return the persistent cross-build cache dir for downloaded tools (CI wipes build/)."""
+    if sys.platform == "win32":
+        base = os.environ.get("LOCALAPPDATA") or (Path.home() / "AppData" / "Local")
+        return Path(base) / "mediahive-build"
+    base = os.environ.get("XDG_CACHE_HOME") or (Path.home() / ".cache")
+    return Path(base) / "mediahive-build"
+
+
+_FFMPEG_STAGING = _build_cache_dir() / "ffmpeg"
+
 # Velopack CLI (dotnet tool package). Runs on the machine's .NET runtime; the
 # produced Setup.exe/Update.exe are native and need no runtime on end-user
 # machines. Pin a version whose tools target an installed .NET major.
@@ -53,7 +63,7 @@ _VPK_URL = (
     f"https://api.nuget.org/v3-flatcontainer/vpk/{_VPK_VERSION}"
     f"/vpk.{_VPK_VERSION}.nupkg"
 )
-_VPK_STAGING = _REPO_ROOT / "build" / "vpk"
+_VPK_STAGING = _build_cache_dir() / f"vpk-{_VPK_VERSION}"
 
 
 def _platform_zip_suffix() -> str:
@@ -73,7 +83,7 @@ def _platform_zip_suffix() -> str:
 
 
 def fetch_ffmpeg() -> Path:
-    """Download latest ffmpeg.exe from BtbN builds into build/ffmpeg/."""
+    """Download latest ffmpeg.exe from BtbN builds into the persistent build cache."""
     dest = _FFMPEG_STAGING / "ffmpeg.exe"
     if dest.exists():
         print(f"ffmpeg already staged at {dest}, skipping download.")
@@ -98,7 +108,7 @@ def fetch_ffmpeg() -> Path:
 
 
 def fetch_macos_arm64_binaries() -> dict[str, Path]:
-    """Download prebuilt macOS arm64 ffmpeg binary into build/ffmpeg/."""
+    """Download prebuilt macOS arm64 ffmpeg binary into the persistent build cache."""
     if sys.platform != "darwin" or platform.machine().lower() not in {
         "arm64",
         "aarch64",
@@ -196,7 +206,7 @@ def ensure_macos_icon() -> Path:
 
 
 def fetch_vpk() -> Path:
-    """Download the Velopack CLI package into build/vpk/ (cached).
+    """Download the Velopack CLI package into the persistent build cache.
 
     Returns the path to vpk.dll, runnable with `dotnet vpk.dll ...`.
     """
@@ -219,15 +229,6 @@ def fetch_vpk() -> Path:
     return vpk_dll
 
 
-_DOTNET_STAGING = _REPO_ROOT / "build" / "dotnet"
-# aka.ms latest-runtime archives per platform (vpk needs .NET >= 8).
-_DOTNET_RUNTIME_URLS = {
-    ("win32", "x64"): "https://aka.ms/dotnet/10.0/dotnet-runtime-win-x64.zip",
-    ("darwin", "arm64"): "https://aka.ms/dotnet/10.0/dotnet-runtime-osx-arm64.tar.gz",
-    ("linux", "x64"): "https://aka.ms/dotnet/10.0/dotnet-runtime-linux-x64.tar.gz",
-}
-
-
 def _dotnet_has_runtime(exe: Path) -> bool:
     """Check that `exe` runs and has Microsoft.NETCore.App >= 8."""
     try:
@@ -250,57 +251,50 @@ def _dotnet_has_runtime(exe: Path) -> bool:
 
 
 def fetch_dotnet() -> str:
-    """Resolve a dotnet host with a modern (>= 8) runtime, bootstrapping one into build/dotnet/ if none is found.
+    """Resolve a dotnet host with a modern (>= 8) runtime from the system.
 
-    A plain `dotnet` may resolve to a runtime-only installation, and
-    long-running services (CI runners) may carry a stale environment without
-    DOTNET_ROOT or scoop paths — so probe known locations explicitly.
+    The .NET SDK is a build prerequisite installed on the build machine —
+    downloading a runtime per build is slow and flaky. A plain `dotnet` may
+    resolve to a runtime-only installation, and long-running services (CI
+    runners) may carry a stale environment without DOTNET_ROOT or scoop
+    paths — so probe known locations explicitly.
     """
     exe_name = "dotnet.exe" if sys.platform == "win32" else "dotnet"
     candidates: list[Path] = []
     root = os.environ.get("DOTNET_ROOT")
     if root:
         candidates.append(Path(root) / exe_name)
-    if sys.platform == "win32":
-        candidates.append(
-            Path(r"C:\ProgramData\scoop\apps\dotnet-sdk\current") / exe_name
-        )
     which = shutil.which("dotnet")
     if which:
         candidates.append(Path(which))
-    staged = _DOTNET_STAGING / exe_name
-    candidates.append(staged)
+    if sys.platform == "win32":
+        candidates += [
+            Path(r"C:\ProgramData\scoop\apps\dotnet-sdk\current") / exe_name,
+            Path(r"C:\Program Files\dotnet") / exe_name,
+        ]
+    elif sys.platform == "darwin":
+        candidates += [
+            Path("/opt/homebrew/bin") / exe_name,
+            Path("/usr/local/share/dotnet") / exe_name,
+        ]
+    else:
+        candidates += [
+            Path("/usr/share/dotnet") / exe_name,
+            Path("/usr/lib/dotnet") / exe_name,
+            Path.home() / ".dotnet" / exe_name,
+        ]
 
     for exe in candidates:
         if exe.exists() and _dotnet_has_runtime(exe):
             print(f"Using dotnet at {exe}")
             return str(exe)
 
-    machine = platform.machine().lower()
-    arch = {"x86_64": "x64", "amd64": "x64", "arm64": "arm64", "aarch64": "arm64"}.get(
-        machine, machine
+    raise RuntimeError(
+        "No dotnet with Microsoft.NETCore.App >= 8 found. "
+        "Install the .NET SDK on this build machine "
+        "(Windows: `scoop install dotnet-sdk`; macOS: `brew install dotnet-sdk`; "
+        "Linux: distro `dotnet-sdk` package or the dotnet-install script)."
     )
-    url = _DOTNET_RUNTIME_URLS.get((sys.platform, arch))
-    if url is None:
-        raise RuntimeError(f"No dotnet runtime download for {sys.platform}/{arch}")
-
-    print(f"Downloading dotnet runtime from {url} ...")
-    with urllib.request.urlopen(url) as resp:
-        data = resp.read()
-
-    _DOTNET_STAGING.mkdir(parents=True, exist_ok=True)
-    if url.endswith(".zip"):
-        with zipfile.ZipFile(io.BytesIO(data)) as zf:
-            zf.extractall(_DOTNET_STAGING)
-    else:
-        with tarfile.open(fileobj=io.BytesIO(data), mode="r:gz") as tf:
-            tf.extractall(_DOTNET_STAGING)
-    staged.chmod(staged.stat().st_mode | stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH)
-
-    if not _dotnet_has_runtime(staged):
-        raise RuntimeError(f"Bootstrapped dotnet at {staged} failed runtime check")
-    print(f"dotnet staged at {_DOTNET_STAGING}")
-    return str(staged)
 
 
 def build_velopack(version: str) -> Path: