ci(linux): build and publish Flatpak on release and path-gated PR CI

Add a ubuntu-24.04 linux-flatpak job that runs build_flatpak.sh from the
shared love payload, wire it into release staging/upload, and mirror a
path-gated Flatpak build in ci.yml when flatpak packaging changes.

.github/workflows/ci.yml

@@ -333,6 +333,56 @@ jobs:
           if-no-files-found: error
           retention-days: 7
 
+  linux-flatpak-changes:
+    name: detect Linux Flatpak changes
+    runs-on: ubuntu-latest
+    outputs:
+      changed: ${{ steps.paths.outputs.changed }}
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+      - id: paths
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha || github.event.before }}
+          HEAD_SHA: ${{ github.sha }}
+        run: |
+          if [ -z "$BASE_SHA" ] || [ "$BASE_SHA" = "0000000000000000000000000000000000000000" ]; then
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+          if git diff --name-only "$BASE_SHA" "$HEAD_SHA" | grep -Eq '^(scripts/build_flatpak\.sh$|flatpak/|scripts/pack_love\.sh$|docs/linux-flatpak\.md$|\.github/workflows/(ci|release)\.yml$)'; then
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "changed=false" >> "$GITHUB_OUTPUT"
+          fi
+
+  linux-flatpak-build:
+    name: Linux Flatpak build
+    needs: linux-flatpak-changes
+    if: needs.linux-flatpak-changes.outputs.changed == 'true'
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v7
+      - name: Install flatpak-builder deps
+        run: |
+          set -euo pipefail
+          sudo apt-get update
+          sudo apt-get install -y flatpak flatpak-builder elfutils imagemagick
+      - name: Build Flatpak bundle
+        run: |
+          set -euo pipefail
+          scripts/build_flatpak.sh --version 0.0.0
+      - name: Upload the Flatpak
+        uses: actions/upload-artifact@v7
+        with:
+          name: gen1recomp-linux-flatpak
+          path: |
+            dist/flatpak/gen1recomp-0.0.0-linux.flatpak
+            dist/flatpak/gen1recomp-0.0.0-linux.flatpak.sha256
+          if-no-files-found: error
+          retention-days: 7
+
   headless:
     name: headless suites (no ROM)
     runs-on: ubuntu-latest

.github/workflows/release.yml

@@ -173,6 +173,38 @@ jobs:
           if-no-files-found: error
           retention-days: 1
 
+  linux-flatpak:
+    name: build Linux Flatpak
+    needs: [version, love-payload]
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v7
+      - name: Install flatpak-builder deps
+        run: |
+          set -euo pipefail
+          sudo apt-get update
+          sudo apt-get install -y flatpak flatpak-builder elfutils imagemagick
+      - name: Download shared payload
+        uses: actions/download-artifact@v8
+        with:
+          name: gen1recomp-release-love
+          path: .bazinga/work
+      - name: Build Flatpak bundle
+        run: |
+          set -euo pipefail
+          scripts/build_flatpak.sh \
+            --version "${{ needs.version.outputs.version }}" \
+            --game-love .bazinga/work/game.love
+      - name: Upload Flatpak release
+        uses: actions/upload-artifact@v7
+        with:
+          name: gen1recomp-linux-flatpak-release
+          path: |
+            dist/flatpak/gen1recomp-${{ needs.version.outputs.version }}-linux.flatpak
+            dist/flatpak/gen1recomp-${{ needs.version.outputs.version }}-linux.flatpak.sha256
+          if-no-files-found: error
+          retention-days: 1
+
   xbox-uwp:
     name: build Xbox UWP release
     needs: [version, love-payload]
@@ -287,7 +319,7 @@ jobs:
           retention-days: 1
 
   release:
-    needs: [version, love-payload, xbox-uwp, linux-arm64, native-tls-win]
+    needs: [version, love-payload, xbox-uwp, linux-arm64, linux-flatpak, native-tls-win]
     runs-on: ${{ fromJSON(github.repository == 'bryanthaboi/gen1recomp' && '["self-hosted", "macOS"]' || '"macos-latest"') }}
 
     steps:
@@ -498,6 +530,13 @@ jobs:
           name: gen1recomp-linux-arm64-release
           path: dist/linux-arm64
 
+      - name: Download Linux Flatpak release
+        if: github.repository == 'bryanthaboi/gen1recomp'
+        uses: actions/download-artifact@v8
+        with:
+          name: gen1recomp-linux-flatpak-release
+          path: dist/flatpak
+
       - name: Stage release assets
         if: github.repository == 'bryanthaboi/gen1recomp'
         id: assets
@@ -525,7 +564,7 @@ jobs:
           chmod +x "$outdir/gen1recomp-${v}-linux-arm64.AppImage"
 
           flatpak_bundle="dist/flatpak/gen1recomp-${v}-linux.flatpak"
-          [ -f "$flatpak_bundle" ] || { echo "::error::$flatpak_bundle not found (expected from scripts/build_flatpak.sh)"; exit 1; }
+          [ -f "$flatpak_bundle" ] || { echo "::error::$flatpak_bundle not found (expected from the linux-flatpak job)"; exit 1; }
           cp "$flatpak_bundle" "$outdir/gen1recomp-${v}-linux.flatpak"
           apk="$(find dist/android/release -name '*.apk' | head -1)"
           [ -n "$apk" ] || { echo "::error::no Android APK found under dist/android/release"; exit 1; }

docs/linux-flatpak.md

@@ -43,4 +43,9 @@ scripts/build_flatpak.sh --version X.Y.Z
 Requires `flatpak` + `flatpak-builder` and the Freedesktop 24.08 runtime from
 Flathub (installed automatically on first build).
 
+Release CI builds the bundle on `ubuntu-24.04` (`linux-flatpak` job) from the
+shared `game.love` payload and publishes `gen1recomp-<ver>-linux.flatpak`
+alongside the AppImages. PR CI path-gates the same script when `flatpak/` or
+`scripts/build_flatpak.sh` change.
+
 Flathub store submission is out of scope for the GitHub bundle channel.