ci: reuse main branch build caches for releases

- Warm Rust, Bun, and core caches on pushes to main
- Save shared caches only on main to avoid duplication across tags
- Isolate build caches by runner
- Skip signing and publishing during cache warmup
- Cancel outdated warmup runs without interrupting releases

.github/workflows/release.yml

@@ -1,7 +1,7 @@
 name: Build portable releases
 
 run-name: >-
-  Portable release ${{ (github.ref_type == 'tag' && github.ref_name) || inputs.release_tag || github.ref_name }}
+  ${{ github.event_name == 'push' && github.ref_type == 'branch' && 'Warm build caches' || 'Portable release' }} ${{ (github.ref_type == 'tag' && github.ref_name) || inputs.release_tag || github.ref_name }}
 
 on:
   workflow_dispatch:
@@ -16,9 +16,15 @@ on:
         default: true
         type: boolean
   push:
+    branches:
+      - main
     tags:
       - 'v*'
 
+concurrency:
+  group: portable-${{ github.ref }}-${{ github.event_name == 'push' && github.ref_type == 'branch' && 'cache' || 'release' }}
+  cancel-in-progress: ${{ github.event_name == 'push' && github.ref_type == 'branch' }}
+
 permissions:
   contents: read
 
@@ -96,6 +102,8 @@ jobs:
             suffix: zip
     runs-on: ${{ matrix.runner }}
     timeout-minutes: 60
+    env:
+      PACKAGE_RELEASE: ${{ github.event_name == 'workflow_dispatch' || github.ref_type == 'tag' }}
     steps:
       - uses: actions/checkout@v7
         with:
@@ -104,21 +112,24 @@ jobs:
         with:
           bun-version: 1.3.14
       - uses: dtolnay/rust-toolchain@1.97.0
-      - name: Cache Bun packages
-        uses: actions/cache@v5
+      - name: Restore Bun packages
+        id: bun-cache
+        uses: actions/cache/restore@v5
         with:
           path: ~/.bun/install/cache
-          key: bun-${{ runner.os }}-${{ runner.arch }}-1.3.14-${{ hashFiles('bun.lock') }}
+          key: bun-${{ matrix.runner }}-1.3.14-${{ hashFiles('bun.lock') }}
           restore-keys: |
-            bun-${{ runner.os }}-${{ runner.arch }}-1.3.14-
+            bun-${{ matrix.runner }}-1.3.14-
       - name: Cache Rust dependencies and build outputs
         uses: Swatinem/rust-cache@v2
         with:
+          key: ${{ matrix.runner }}
           workspaces: src-tauri -> target
           cache-workspace-crates: true
-          cache-on-failure: true
-      - name: Cache bundled core archive
-        uses: actions/cache@v5
+          save-if: ${{ github.ref == format('refs/heads/{0}', github.event.repository.default_branch) }}
+      - name: Restore bundled core archive
+        id: core-cache
+        uses: actions/cache/restore@v5
         with:
           path: cpa-core
           key: core-v2-${{ matrix.os }}-${{ matrix.arch }}-${{ hashFiles('core-version.txt') }}
@@ -154,8 +165,20 @@ jobs:
           --arch "${{ matrix.arch }}"
           --download true
         shell: bash
+      - name: Save Bun packages
+        if: github.ref == format('refs/heads/{0}', github.event.repository.default_branch) && steps.bun-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@v5
+        with:
+          path: ~/.bun/install/cache
+          key: ${{ steps.bun-cache.outputs.cache-primary-key }}
+      - name: Save bundled core archive
+        if: github.ref == format('refs/heads/{0}', github.event.repository.default_branch) && steps.core-cache.outputs.cache-hit != 'true'
+        uses: actions/cache/save@v5
+        with:
+          path: cpa-core
+          key: ${{ steps.core-cache.outputs.cache-primary-key }}
       - name: Build signed macOS DMG
-        if: matrix.os == 'darwin'
+        if: env.PACKAGE_RELEASE == 'true' && matrix.os == 'darwin'
         shell: bash
         env:
           APPLE_CERTIFICATE: ${{ secrets.APPLE_CERTIFICATE }}
@@ -252,14 +275,15 @@ jobs:
             --wait
           xcrun stapler staple "$output_dmg"
       - name: Archive Linux release
-        if: matrix.os == 'linux'
+        if: env.PACKAGE_RELEASE == 'true' && matrix.os == 'linux'
         run: tar -czf "${{ steps.package.outputs.stem }}.tar.gz" -C release "${{ steps.package.outputs.stem }}"
       - name: Archive Windows release
-        if: matrix.os == 'windows'
+        if: env.PACKAGE_RELEASE == 'true' && matrix.os == 'windows'
         shell: pwsh
         run: |
           Compress-Archive -Path "release/${{ steps.package.outputs.stem }}" -DestinationPath "${{ steps.package.outputs.stem }}.zip"
       - uses: actions/upload-artifact@v7
+        if: env.PACKAGE_RELEASE == 'true'
         with:
           name: ${{ steps.package.outputs.stem }}
           path: ${{ steps.package.outputs.stem }}.${{ matrix.suffix }}