ci: log gitea API error responses

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016tGMoEdMRnHsABmDbK3H7o

ci.nix

@@ -1,10 +1,17 @@
 { lib, pkgs }:
+let
+  # vulnix's bundled nix-2.34 broke its own --experimental-features detection
+  nixConf = pkgs.writeText "ci-nix.conf" "experimental-features = nix-command flakes";
+in
 # tools must track ci.py's subprocess calls; nix stays ambient (uses the
 # runner's own nix, not a pinned one).
 pkgs.writers.writePython3Bin "ci" {
   flakeIgnore = [ "E501" ];
   libraries = [ pkgs.python3Packages.subprocess-tee ];
   makeWrapperArgs = [
+    "--set-default"
+    "NIX_USER_CONF_FILES"
+    (toString nixConf)
     "--prefix"
     "PATH"
     ":"

ci.py

@@ -18,7 +18,8 @@ def run(*args, **kw):
 
 
 def nix(*args):
-    return subprocess_tee.run(("nix", "--extra-experimental-features", "nix-command flakes", "-L", *args), check=True, text=True).stdout
+    # tee to stderr - stdout leaks into GITHUB_OUTPUT $() captures
+    return subprocess_tee.run(("nix", "--extra-experimental-features", "nix-command flakes", "-L", *args), check=True, text=True, stdout=sys.stderr).stdout
 
 
 def git(*args, check=True):
@@ -32,8 +33,11 @@ def gitea(method, path, body=None):
     req.add_header("Authorization", f'token {os.environ["GH_TOKEN"]}')
     if data is not None:
         req.add_header("Content-Type", "application/json")
-    with urllib.request.urlopen(req) as resp:
+    try:
-        raw = resp.read()
+        with urllib.request.urlopen(req) as resp:
+            raw = resp.read()
+    except urllib.error.HTTPError as e:
+        sys.exit(f"gitea {method} {path}: {e.code} {e.reason}\n{e.read().decode()}")
     return json.loads(raw) if raw else None
 
 
@@ -254,7 +258,7 @@ def format_vulnix(vulns):
 
 def vulnix(args):
     paths = list(build_hosts(args.ref).values())
-    result = run("vulnix", "-j", "-C", *paths, capture_output=True)
+    result = run("vulnix", "-j", *paths, capture_output=True)
     if result.returncode not in (0, 2):
         print(result.stderr, file=sys.stderr)
         sys.exit(result.returncode)