feat: src/launcher.py — Python update launcher (HTTP, app/app.old swap)

Launcher core that reuses services/update_service: seed default config into
~/.cmbot on first run, check the manifest, download the release zip, verify
SHA-256, extract, validate version, swap into app/ (keeping app.old/ for
rollback), then launch app/CMBot.exe. Degrades to the local version on any
failure; checks install-root writability before updating.

- update_service: UpdateInfo gains sha256/size/min_supported; release URL
  resolved to absolute; extract make_auth_header + add download() helper
- tests/test_launcher.py: 11 tests (seed, find-root, swap, sha mismatch,
  no-update); also verified end-to-end against a local HTTP server

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/services/update_service.py

@@ -26,9 +26,12 @@ MANIFEST_NAME = "manifest.json"
 class UpdateInfo:
     """A newer version advertised by the update source."""
     version: str
-    source: str            # folder or URL the user opens to get the new version
+    source: str            # absolute zip URL (http) or folder/path to the new version
     notes: str = ""
     mandatory: bool = False
+    sha256: str = ""       # expected hash of the release zip (launcher verifies)
+    size: int = 0          # release zip size in bytes (0 = unknown)
+    min_supported: str = ""
 
 
 def parse_version(text) -> tuple:
@@ -70,17 +73,35 @@ def _manifest_url(update_source):
     return parse.urljoin(source, MANIFEST_NAME)
 
 
+def make_auth_header(update_user="", update_pass=""):
+    """Return an HTTP Basic Auth header dict, or {} when no credentials."""
+    if not (update_user or update_pass):
+        return {}
+    raw = "{}:{}".format(update_user or "", update_pass or "").encode("utf-8")
+    return {"Authorization": "Basic {}".format(base64.b64encode(raw).decode("ascii"))}
+
+
+def download(url, dest, update_user="", update_pass="", timeout=120):
+    """Download *url* to *dest* (Path/str) with optional Basic Auth.
+
+    Streams in chunks so large release zips don't load fully into memory.
+    Raises (OSError / URLError) on failure — callers handle degradation.
+    """
+    headers = {"User-Agent": "CMBot"}
+    headers.update(make_auth_header(update_user, update_pass))
+    req = request.Request(url, headers=headers)
+    with request.urlopen(req, timeout=timeout) as response, open(str(dest), "wb") as f:
+        while True:
+            chunk = response.read(65536)
+            if not chunk:
+                break
+            f.write(chunk)
+
+
 def _load_http_manifest(update_source, update_user="", update_pass=""):
     url = _manifest_url(update_source)
-    headers = {
-        "Accept": "application/json",
-        "User-Agent": "CMBot",
-    }
-    if update_user or update_pass:
-        raw = "{}:{}".format(update_user or "", update_pass or "").encode("utf-8")
-        headers["Authorization"] = "Basic {}".format(
-            base64.b64encode(raw).decode("ascii")
-        )
+    headers = {"Accept": "application/json", "User-Agent": "CMBot"}
+    headers.update(make_auth_header(update_user, update_pass))
 
     req = request.Request(url, headers=headers)
     with request.urlopen(req, timeout=5) as response:
@@ -136,11 +157,18 @@ def check_for_update(
     source = str(data.get("url", "") or data.get("source", "")).strip()
     if not source:
         source = str(update_source)
+    elif _is_http_source(update_source):
+        # Resolve a relative release URL against the manifest URL so callers
+        # (in-app banner / launcher) always get a directly usable absolute URL.
+        source = parse.urljoin(_manifest_url(update_source), source)
     info = UpdateInfo(
         version=version,
         source=source,
         notes=str(data.get("notes", "")),
         mandatory=bool(data.get("mandatory", False)),
+        sha256=str(data.get("sha256", "")).strip(),
+        size=int(data.get("size", 0) or 0),
+        min_supported=str(data.get("min_supported", "")).strip(),
     )
     logger.info("Update available: v%s (current v%s)", version, current_version)
     return info