Make npm publish workflow idempotent with retries

Skip packages already published to npm, and retry failed publishes
up to 3 times with a 30-second delay. After a failed attempt, also
check if the version was published by a concurrent run (TOCTOU).

[ci skip]

Assisted-by: OpenCode:deepseek-v4-pro
Assisted-by: Codex:gpt-5.5

Author: dahlia

.github/workflows/build.yaml

@@ -55,12 +55,39 @@ jobs:
             echo "Skipping private package: $pkg"
             continue
           fi
-          npm publish \
-            --logs-dir=. \
-            --provenance \
-            --access public \
-            --tag "$TAG" \
-            "$pkg" \
-            || grep "Cannot publish over previously published version" *.log
+          PKG_NAME=$(tar -xOzf "$pkg" package/package.json | jq -r .name)
+          PKG_VERSION=$(tar -xOzf "$pkg" package/package.json | jq -r .version)
+          # Skip if this version is already published
+          if npm view "$PKG_NAME@$PKG_VERSION" version > /dev/null 2>&1; then
+            echo "Skipping already published: $PKG_NAME@$PKG_VERSION"
+            continue
+          fi
+          # Publish with retry (up to 3 attempts)
+          success=false
+          for attempt in 1 2 3; do
+            echo "Publishing $PKG_NAME@$PKG_VERSION (attempt $attempt/3)"
+            if npm publish \
+              --logs-dir=. \
+              --provenance \
+              --access public \
+              --tag "$TAG" \
+              "$pkg"; then
+              echo "Successfully published $PKG_NAME@$PKG_VERSION"
+              success=true
+              break
+            fi
+            # Check if version was published by another concurrent run
+            if npm view "$PKG_NAME@$PKG_VERSION" version > /dev/null 2>&1; then
+              echo "Version $PKG_VERSION already exists on npm (published by another run)"
+              success=true
+              break
+            fi
+            echo "Failed to publish $PKG_NAME@$PKG_VERSION, waiting 30 seconds..."
+            sleep 30
+          done
+          if [ "$success" = false ]; then
+            echo "ERROR: Failed to publish $PKG_NAME@$PKG_VERSION after 3 attempts"
+            exit 1
+          fi
           rm -f *.log
         done