fix(build): poll for ext-<version> release in tag-push build-web (race fix)

Cutting a release fires BOTH the push-to-main workflow AND the push-to-tag
workflow in parallel. main-push runs sign-extension (AMO round-trip 1-5min)
then publishes the ext-<version> Forgejo release; tag-push skips
sign-extension (gated to main) and races straight to build-web's Download
XPI step. Tag-push lost every time — got 404 from
releases/tags/ext-<version> before main-push had finished signing.

v26.05.27.0 hit this: tag-push build-web died on exit 22 because the
ext-1.0.4 release wasn't published yet (it arrived ~4min later).

Fix: wrap the release lookup in a 20-iteration sleep+retry loop, 30s
between attempts (10min total upper bound, generous for AMO). main-push's
signing eventually publishes the release; tag-push picks it up on a later
poll. No more manual rerun of the failed job after every release cut.

Banked the trap as reference_tag_push_main_push_race.md — same shape will
recur any time a tag-push workflow consumes a main-push-produced artifact.

.forgejo/workflows/build.yml

@@ -173,24 +173,51 @@ jobs:
         # same source code as the preceding main-push build but with an
         # immutable version tag — they need the XPI too, otherwise the
         # versioned image ships without the signed extension.
+        #
+        # Tag-push vs main-push race (operator-flagged 2026-05-27 after
+        # v26.05.27.0 hit it): a release cut fires BOTH workflows almost
+        # simultaneously. Main-push runs sign-extension (1-5min AMO round
+        # trip) before publishing the ext-<version> release; tag-push
+        # skips sign-extension (gated to main) and races straight to
+        # this download step. Tag-push lost every time. Fix: poll the
+        # ext-<version> release endpoint with a sleep+retry loop (30s
+        # for up to 10min total) before giving up. Main-push's signing
+        # eventually wins and tag-push picks the release up on a later
+        # iteration.
         if: github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/')
         env:
           TOKEN: ${{ secrets.RELEASE_TOKEN }}
         run: |
           set -eux
           VERSION=$(grep -E '"version"' extension/package.json | head -1 | sed -E 's/.*"version"[[:space:]]*:[[:space:]]*"([^"]+)".*/\1/')
-          # Look up the ext-<version> release; extract the .xpi asset's
-          # browser_download_url (Forgejo's /releases/assets/<id> endpoint
-          # returns ASSET METADATA, not the binary blob — operator-flagged
-          # 2026-05-26: my prior code curl'd the metadata endpoint without
-          # -f and wrote the resulting 404-page-not-found text into
-          # fabledcurator-*.xpi, which Firefox then rejected as "corrupt").
-          # browser_download_url is the canonical binary endpoint and is
-          # also publicly accessible (no token needed) but we pass the
-          # token anyway for symmetry with private-repo support.
-          curl -sf -H "Authorization: token $TOKEN" \
-            "https://git.fabledsword.com/api/v1/repos/bvandeusen/FabledCurator/releases/tags/ext-$VERSION" \
-            -o release.json
+          # Poll for the ext-<version> release. main-push's sign-extension
+          # step (AMO round-trip, 1-5min) needs to finish + upload before
+          # tag-push can fetch. 30s * 20 = up to 10min wait, then hard-fail.
+          for attempt in $(seq 1 20); do
+            STATUS=$(curl -s -o release.json -w "%{http_code}" \
+              -H "Authorization: token $TOKEN" \
+              "https://git.fabledsword.com/api/v1/repos/bvandeusen/FabledCurator/releases/tags/ext-$VERSION" || echo 000)
+            if [ "$STATUS" = "200" ]; then
+              echo "Found ext-$VERSION release on attempt $attempt"
+              break
+            fi
+            if [ "$attempt" = "20" ]; then
+              echo "ERROR: ext-$VERSION release not available after 10min of polling"
+              echo "Last HTTP status: $STATUS"
+              exit 1
+            fi
+            echo "Attempt $attempt: ext-$VERSION not yet published (HTTP $STATUS); sleeping 30s"
+            sleep 30
+          done
+          # Extract the .xpi asset's browser_download_url (Forgejo's
+          # /releases/assets/<id> endpoint returns ASSET METADATA, not
+          # the binary blob — operator-flagged 2026-05-26: my prior
+          # code curl'd the metadata endpoint without -f and wrote the
+          # resulting 404-page-not-found text into fabledcurator-*.xpi,
+          # which Firefox then rejected as "corrupt").
+          # browser_download_url is the canonical binary endpoint and
+          # is also publicly accessible (no token needed) but we pass
+          # the token anyway for symmetry with private-repo support.
           DOWNLOAD_URL=$(python3 -c "import json; r=json.load(open('release.json')); xpis=[a for a in r.get('assets', []) if a.get('name','').endswith('.xpi')]; print(xpis[0]['browser_download_url'])")
           test -n "$DOWNLOAD_URL"
           echo "Downloading XPI from: $DOWNLOAD_URL"