ci: registry-gc — read branches with the Actions token, not PACKAGE_TOKEN

The dry-run failed with HTTP 403 on the branches API: PACKAGE_TOKEN is a
package-scoped token (registry push/delete) and can't read repo branches. Split
by capability: branch reads now use the automatic Actions token (github.token,
repo read via 'permissions: contents: read'); package list + delete keep
PACKAGE_TOKEN. Also replaced the bare 'curl -f' failures with a get() helper that
reports the HTTP code + a token-scope hint, so an auth problem can't look like
'no results' (which would otherwise skew the reconcile).

.gitea/workflows/registry-gc.yaml

@@ -23,7 +23,9 @@
 # repo variable REGISTRY_GC_ENABLE=true — so you can eyeball a scheduled dry-run
 # first, then flip the variable to let it prune automatically.
 #
-# Needs the existing PACKAGE_TOKEN secret (write:package scope, which the
+# TOKENS (two, by capability — a package token can't read branches, hence the
+# original 403): branch reads use the automatic Actions token (github.token,
+# repo read); package list + delete use PACKAGE_TOKEN (write:package, which the
 # registry-push token already has). Only touches images THIS repo builds; the
 # fleet-kiosk image is owned by the kiosk-app submodule's own CI.
 
@@ -40,6 +42,9 @@ on:
         type: boolean
         default: true
 
+permissions:
+  contents: read                 # branch listing via the auto Actions token
+
 concurrency:
   group: registry-gc
   cancel-in-progress: false
@@ -53,7 +58,8 @@ jobs:
       SERVER: "https://git.bitasylum.org"
       OWNER: ${{ github.repository_owner }}
       REPO: ${{ github.repository }}
-      TOKEN: ${{ secrets.PACKAGE_TOKEN }}
+      REPO_TOKEN: ${{ github.token }}            # auto Actions token: repo/branch reads
+      PKG_TOKEN: ${{ secrets.PACKAGE_TOKEN }}    # package list + delete (write:package)
       EVENT: ${{ github.event_name }}
       DISPATCH_DRY: ${{ inputs.dry_run }}
       GC_ENABLE: ${{ vars.REGISTRY_GC_ENABLE }}
@@ -69,7 +75,27 @@ jobs:
           command -v jq >/dev/null 2>&1 || { sudo apt-get update -qq && sudo apt-get install -y -qq jq; }
 
           API="${SERVER}/api/v1"
-          auth=(-H "Authorization: token ${TOKEN}" -H "Accept: application/json")
+
+          # Authenticated GET. $1 = which token (repo|pkg), $2 = url. Echoes the
+          # body on 2xx; on anything else prints an actionable error and exits
+          # (so a scope/auth problem can never be mistaken for "no results").
+          get() {
+            local who="$1" url="$2" tok tmp code body
+            case "$who" in repo) tok="$REPO_TOKEN";; pkg) tok="$PKG_TOKEN";; esac
+            tmp="$(mktemp)"
+            code="$(curl -sS --retry 3 -o "$tmp" -w '%{http_code}' \
+                     -H "Authorization: token ${tok}" -H "Accept: application/json" "$url" || echo 000)"
+            body="$(cat "$tmp")"; rm -f "$tmp"
+            case "$code" in
+              2*) printf '%s' "$body"; return 0 ;;
+              401|403)
+                echo "::error::GET ${url} -> HTTP ${code} (token '${who}' lacks scope). branches need repo read (github.token); packages need read/write:package (PACKAGE_TOKEN)." >&2
+                exit 1 ;;
+              *)
+                echo "::error::GET ${url} -> HTTP ${code}" >&2
+                exit 1 ;;
+            esac
+          }
 
           # ---- dry-run resolution ------------------------------------------
           if [ "$EVENT" = "workflow_dispatch" ]; then
@@ -91,7 +117,7 @@ jobs:
           live=" main "        # main is always protected, even if listing is odd
           total=0 page=1
           while :; do
-            resp="$(curl -fsSL --retry 3 "${auth[@]}" "${API}/repos/${REPO}/branches?limit=50&page=${page}")"
+            resp="$(get repo "${API}/repos/${REPO}/branches?limit=50&page=${page}")"
             cnt="$(printf '%s' "$resp" | jq 'length')"
             [ "$cnt" -eq 0 ] && break
             while IFS= read -r b; do
@@ -112,7 +138,7 @@ jobs:
           for img in $IMAGES; do
             page=1
             while :; do
-              resp="$(curl -fsSL --retry 3 "${auth[@]}" "${API}/packages/${OWNER}?type=container&q=${img}&limit=50&page=${page}")"
+              resp="$(get pkg "${API}/packages/${OWNER}?type=container&q=${img}&limit=50&page=${page}")"
               cnt="$(printf '%s' "$resp" | jq 'length')"
               [ "$cnt" -eq 0 ] && break
               while IFS= read -r ver; do
@@ -143,7 +169,9 @@ jobs:
                 orphans=$((orphans + 1))
                 echo "ORPHAN  ${img}:${ver}"
                 if [ "$DRY" != "true" ]; then
-                  code="$(curl -sS -o /dev/null -w '%{http_code}' -X DELETE "${auth[@]}" "${API}/packages/${OWNER}/container/${img}/${ver}" || echo 000)"
+                  code="$(curl -sS -o /dev/null -w '%{http_code}' -X DELETE \
+                           -H "Authorization: token ${PKG_TOKEN}" \
+                           "${API}/packages/${OWNER}/container/${img}/${ver}" || echo 000)"
                   case "$code" in
                     2*) deleted=$((deleted + 1)); echo "  deleted ${img}:${ver}" ;;
                     *)  failed=$((failed + 1)); echo "::warning::delete ${img}:${ver} returned HTTP ${code}" ;;