ci: survive a revoked GITEA_BUILD_TOKEN on public commit reads

Follow-up to a2f0a4a, which documented the hazard; this removes it.

resolve-versions read three PUBLIC Gitea repos with `curl -sf -H "$AUTH_HEADER"`.
Gitea rejects an invalid token rather than ignoring it, so the token turned a
read that works anonymously into a hard failure:

  no Authorization header    200
  empty token (secret unset) 200   <- absent secret was always safe
  garbage/revoked token      401   <- stale secret broke the release

A revoked GITEA_BUILD_TOKEN therefore failed resolve-versions via require_sha,
presenting as connectivity or an API fault, on data any anonymous client could
fetch. Hit exactly that failure mode today with an expired PAT.

New gitea_sha() helper tries authed, and on 401/403 retries anonymously with a
loud stderr warning naming the token as the cause. Deliberate choices:

- non-200 after the retry emits nothing and returns 0, so require_sha still
  raises the explicit abort — the helper never invents a fallback ref, which is
  the property the surrounding code exists to guarantee
- warnings go to stderr, NOT as ::warning:: annotations: the function's stdout
  IS the SHA, so an annotation there would be captured into the ref
- the header is still sent first, so a private repo keeps working

Verified by extracting the function from the YAML step body (so the test ran the
committed text, not a copy) and calling it against live Gitea:

  valid token        -> 0e1369e6b496 (pi-toolkit)
  REVOKED token      -> warns, retries anon, f60cf9c73205 (mempalace-toolkit)
  unset secret       -> 98eb07bce60a (pi-extensions)
  nonexistent repo   -> empty + HTTP 404 warning, so require_sha aborts

Behaviour unchanged on the happy path: all three SHAs are byte-identical to the
ones the v1.8.1 release run resolved with the old curl code. `bash -n` clean on
the extracted step body; YAML re-parsed.

.gitea/workflows/docker-publish.yml

@@ -177,6 +177,40 @@ jobs:
             fi
           }
 
+          # Read a commit SHA from Gitea, surviving a bad build token.
+          #
+          # These repos are public (see the note at the call sites), so auth is
+          # a convenience, not a requirement — but Gitea REJECTS an invalid
+          # token (401) rather than ignoring it, so a revoked or malformed
+          # GITEA_BUILD_TOKEN could fail an entire release on reads that work
+          # fine anonymously. An ABSENT secret was always safe (Gitea ignores an
+          # empty `token ` value and serves the request, 200); a STALE one was
+          # not. So: try authed, and on 401/403 retry anonymously.
+          #
+          # A non-200 after that emits nothing and returns 0 deliberately, so
+          # require_sha raises the loud explicit abort rather than this helper
+          # inventing a fallback ref.
+          #
+          # Messages go to STDERR, not as ::warning:: annotations: this
+          # function's stdout IS the SHA, so anything written there would be
+          # captured into the ref by the command substitution.
+          gitea_sha() { # $1=repo
+            local repo="$1" url resp code
+            url="https://gitea.jordbo.se/api/v1/repos/joakimp/${repo}/commits?limit=1&sha=main"
+            resp=$(curl -s -w '\n%{http_code}' -H "$AUTH_HEADER" "$url" || printf '\n000')
+            code=${resp##*$'\n'}
+            if [ "$code" = "401" ] || [ "$code" = "403" ]; then
+              printf 'WARNING: Gitea rejected the build token for %s (HTTP %s); retrying anonymously. The read should succeed (public repo), but GITEA_BUILD_TOKEN is stale or malformed and should be rotated.\n' "$repo" "$code" >&2
+              resp=$(curl -s -w '\n%{http_code}' "$url" || printf '\n000')
+              code=${resp##*$'\n'}
+            fi
+            if [ "$code" != "200" ]; then
+              printf 'WARNING: Gitea commit lookup for %s returned HTTP %s\n' "$repo" "$code" >&2
+              return 0
+            fi
+            printf '%s' "${resp%$'\n'*}" | jq -r '.[0].sha // empty' 2>/dev/null || true
+          }
+
           # ── pi version: from the PIN, not from npm `latest` ───────────
           # Until v1.7.0 this followed npm `latest`, which meant every release
           # silently adopted whatever pi had shipped that morning — unaudited —
@@ -256,13 +290,9 @@ jobs:
           # require_sha failure that reads like an API or network fault. If this
           # step ever fails on a repo you can browse anonymously, suspect the
           # token before you suspect Gitea.
-          TOOLKIT_REF=$(curl -sf -H "$AUTH_HEADER" \
+          TOOLKIT_REF=$(gitea_sha pi-toolkit)
-            "https://gitea.jordbo.se/api/v1/repos/joakimp/pi-toolkit/commits?limit=1&sha=main" \
-            | jq -r '.[0].sha // empty' 2>/dev/null || true)
           require_sha PI_TOOLKIT_REF "$TOOLKIT_REF"
-          EXTENSIONS_REF=$(curl -sf -H "$AUTH_HEADER" \
+          EXTENSIONS_REF=$(gitea_sha pi-extensions)
-            "https://gitea.jordbo.se/api/v1/repos/joakimp/pi-extensions/commits?limit=1&sha=main" \
-            | jq -r '.[0].sha // empty' 2>/dev/null || true)
           require_sha PI_EXTENSIONS_REF "$EXTENSIONS_REF"
           echo "toolkit_ref=${TOOLKIT_REF}"        >> "$GITHUB_OUTPUT"
           echo "extensions_ref=${EXTENSIONS_REF}"  >> "$GITHUB_OUTPUT"
@@ -272,9 +302,7 @@ jobs:
           # into the base-decide hash (see that job) to force a base rebuild
           # when the toolkit moves — otherwise a toolkit-only fix silently
           # fails to land unless Dockerfile.base itself changes.
-          MEMPALACE_TOOLKIT_REF=$(curl -sf -H "$AUTH_HEADER" \
+          MEMPALACE_TOOLKIT_REF=$(gitea_sha mempalace-toolkit)
-            "https://gitea.jordbo.se/api/v1/repos/joakimp/mempalace-toolkit/commits?limit=1&sha=main" \
-            | jq -r '.[0].sha // empty' 2>/dev/null || true)
           require_sha MEMPALACE_TOOLKIT_REF "$MEMPALACE_TOOLKIT_REF"
           echo "mempalace_toolkit_ref=${MEMPALACE_TOOLKIT_REF}" >> "$GITHUB_OUTPUT"