ci: publish lib-vt xcframework in tip releases

Add a build-lib-vt-xcframework job to the release-tip workflow that
builds the universal xcframework with ReleaseFast, zips it, signs
it with minisign, and uploads it to both the GitHub Release and R2
blob storage. Consumers can pull the xcframework zip from the tip
release or by commit hash from tip.files.ghostty.org.

.github/workflows/release-tip.yml

@@ -260,6 +260,91 @@ jobs:
             libghostty-vt-source.tar.gz.minisig
           token: ${{ secrets.GH_RELEASE_TOKEN }}
 
+  build-lib-vt-xcframework:
+    needs: [setup]
+    if: |
+      needs.setup.outputs.should_skip != 'true' &&
+      (
+        github.event_name == 'workflow_dispatch' ||
+        (
+          github.repository_owner == 'ghostty-org' &&
+          github.ref_name == 'main'
+        )
+      )
+    runs-on: namespace-profile-ghostty-macos-tahoe
+    env:
+      GHOSTTY_COMMIT_LONG: ${{ needs.setup.outputs.commit_long }}
+      ZIG_LOCAL_CACHE_DIR: /Users/runner/zig/local-cache
+      ZIG_GLOBAL_CACHE_DIR: /Users/runner/zig/global-cache
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Setup Cache
+        uses: namespacelabs/nscloud-cache-action@a90bb5d4b27522ce881c6e98eebd7d7e6d1653f9 # v1.4.2
+        with:
+          cache: |
+            xcode
+          path: |
+            /Users/runner/zig
+
+      # TODO(tahoe): https://github.com/NixOS/nix/issues/13342
+      - uses: DeterminateSystems/nix-installer-action@main
+        with:
+          determinate: true
+      - uses: cachix/cachix-action@1eb2ef646ac0255473d23a5907ad7b04ce94065c # v17
+        with:
+          name: ghostty
+          authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
+
+      - name: Xcode Select
+        run: sudo xcode-select -s /Applications/Xcode_26.3.app
+
+      - name: Build XCFramework
+        run: nix develop -c zig build -Demit-lib-vt -Doptimize=ReleaseFast
+
+      - name: Zip XCFramework
+        run: |
+          cd zig-out/lib
+          zip -9 -r ../../ghostty-vt.xcframework.zip ghostty-vt.xcframework
+
+      - name: Sign XCFramework
+        run: |
+          echo -n "${{ secrets.MINISIGN_KEY }}" > minisign.key
+          echo -n "${{ secrets.MINISIGN_PASSWORD }}" > minisign.password
+          nix develop -c minisign -S -m ghostty-vt.xcframework.zip -s minisign.key < minisign.password
+
+      - name: Update Release
+        uses: softprops/action-gh-release@153bb8e04406b158c6c84fc1615b65b24149a1fe # v2.6.1
+        with:
+          name: 'Ghostty Tip ("Nightly")'
+          prerelease: true
+          tag_name: tip
+          target_commitish: ${{ github.sha }}
+          files: |
+            ghostty-vt.xcframework.zip
+            ghostty-vt.xcframework.zip.minisig
+          token: ${{ secrets.GH_RELEASE_TOKEN }}
+
+      - name: Prep R2 Storage
+        run: |
+          mkdir -p blob/${GHOSTTY_COMMIT_LONG}
+          cp ghostty-vt.xcframework.zip blob/${GHOSTTY_COMMIT_LONG}/ghostty-vt.xcframework.zip
+      - name: Upload to R2
+        uses: ryand56/r2-upload-action@b801a390acbdeb034c5e684ff5e1361c06639e7c # v1.4
+        with:
+          r2-account-id: ${{ secrets.CF_R2_TIP_ACCOUNT_ID }}
+          r2-access-key-id: ${{ secrets.CF_R2_TIP_AWS_KEY }}
+          r2-secret-access-key: ${{ secrets.CF_R2_TIP_SECRET_KEY }}
+          r2-bucket: ghostty-tip
+          source-dir: blob
+          destination-dir: ./
+
+      - name: Echo Release URLs
+        run: |
+          echo "Release URLs:"
+          echo "  XCFramework: https://tip.files.ghostty.org/${GHOSTTY_COMMIT_LONG}/ghostty-vt.xcframework.zip"
+
   build-macos:
     needs: [setup]
     if: |