refactor: simplify ccache to single directory with restore-keys fallback

Removed split ccache configuration (~/.ccache-main + ~/.ccache-current).

The split had an edge case: building a feature branch before main branch
cache is primed results in double ccache disk usage:
- Feature branch builds first → populates ~/.ccache-current (2G max_size)
- Main branch builds later → populates ~/.ccache-main (2G max_size)
- Next feature branch build → restores both caches (4G total)

This doubles ccache disk usage unnecessarily on GitHub-hosted runners.

New single-directory approach:
- Single ~/.ccache directory for all branches
- Branch-specific keys with restore-keys fallback to main branch
- Cache actions handle cross-branch sharing via partial-match mode
- Simpler and prevents double disk usage edge case

Changes:
- xahau-configure-ccache: Single cache_dir input, removed branch logic
- xahau-ga-build: Single restore/save step, uses restore-keys for fallback
- xahau-ga-nix: Removed is_main_branch parameter

Disk usage: 2G max (vs 4G worst case with split)

.github/actions/xahau-configure-ccache/action.yml

@@ -2,6 +2,10 @@ name: 'Configure ccache'
 description: 'Sets up ccache with consistent configuration'
 
 inputs:
+  cache_dir:
+    description: 'Path to ccache directory'
+    required: false
+    default: '~/.ccache'
   max_size:
     description: 'Maximum cache size'
     required: false
@@ -14,18 +18,6 @@ inputs:
     description: 'How to check compiler for changes'
     required: false
     default: 'content'
-  is_main_branch:
-    description: 'Whether the current branch is the main branch'
-    required: false
-    default: 'false'
-  main_cache_dir:
-    description: 'Path to the main branch cache directory'
-    required: false
-    default: '~/.ccache-main'
-  current_cache_dir:
-    description: 'Path to the current branch cache directory'
-    required: false
-    default: '~/.ccache-current'
 
 runs:
   using: 'composite'
@@ -33,31 +25,20 @@ runs:
     - name: Configure ccache
       shell: bash
       run: |
-        # Create cache directories
-        mkdir -p ${{ inputs.main_cache_dir }} ${{ inputs.current_cache_dir }}
-        
-        # Set compiler check globally
-        ccache -o compiler_check=${{ inputs.compiler_check }}
-        
-        # Use a single config file location
-        mkdir -p ~/.ccache
-        export CONF_PATH="$HOME/.ccache/ccache.conf"
-        
-        # Apply common settings
-        echo "max_size = ${{ inputs.max_size }}" > "$CONF_PATH"
-        echo "hash_dir = ${{ inputs.hash_dir }}" >> "$CONF_PATH"
-        echo "compiler_check = ${{ inputs.compiler_check }}" >> "$CONF_PATH"
-        
-        if [ "${{ inputs.is_main_branch }}" == "true" ]; then
-          # Main branch: use main branch cache
-          ccache --set-config=cache_dir="${{ inputs.main_cache_dir }}"
-          echo "CCACHE_DIR=${{ inputs.main_cache_dir }}" >> $GITHUB_ENV
-        else
-          # Feature branch: use current branch cache with main as secondary
-          ccache --set-config=cache_dir="${{ inputs.current_cache_dir }}"
-          ccache --set-config=secondary_storage="file:${{ inputs.main_cache_dir }}"
-          echo "CCACHE_DIR=${{ inputs.current_cache_dir }}" >> $GITHUB_ENV
-        fi
-        
-        ccache -p # Print config for verification
-        ccache -z # Zero statistics before the build
+        # Create cache directory
+        mkdir -p ${{ inputs.cache_dir }}
+
+        # Configure ccache settings
+        ccache --set-config=cache_dir="${{ inputs.cache_dir }}"
+        ccache --set-config=max_size=${{ inputs.max_size }}
+        ccache --set-config=hash_dir=${{ inputs.hash_dir }}
+        ccache --set-config=compiler_check=${{ inputs.compiler_check }}
+
+        # Export for use by build tools
+        echo "CCACHE_DIR=${{ inputs.cache_dir }}" >> $GITHUB_ENV
+
+        # Print config for verification
+        ccache -p
+
+        # Zero statistics before the build
+        ccache -z

.github/actions/xahau-ga-build/action.yml

@@ -65,25 +65,12 @@ runs:
         SAFE_BRANCH=$(echo "${{ github.ref_name }}" | tr -c 'a-zA-Z0-9_.-' '-')
         echo "name=${SAFE_BRANCH}" >> $GITHUB_OUTPUT
 
-    - name: Restore ccache directory for default branch
+    - name: Restore ccache directory
       if: inputs.ccache_enabled == 'true'
       id: ccache-restore
       uses: ./.github/actions/xahau-actions-cache-restore
       with:
-        path: ~/.ccache-main
-        key: ${{ runner.os }}-ccache-v${{ inputs.cache_version }}-${{ inputs.compiler-id }}-${{ inputs.configuration }}-${{ inputs.main_branch }}
-        restore-keys: |
-          ${{ runner.os }}-ccache-v${{ inputs.cache_version }}-${{ inputs.compiler-id }}-${{ inputs.configuration }}-
-          ${{ runner.os }}-ccache-v${{ inputs.cache_version }}-${{ inputs.compiler-id }}-
-        aws-access-key-id: ${{ inputs.aws-access-key-id }}
-        aws-secret-access-key: ${{ inputs.aws-secret-access-key }}
-
-    - name: Restore ccache directory for current branch
-      if: inputs.ccache_enabled == 'true' && steps.safe-branch.outputs.name != inputs.main_branch
-      id: ccache-restore-current-branch
-      uses: ./.github/actions/xahau-actions-cache-restore
-      with:
-        path: ~/.ccache-current
+        path: ~/.ccache
         key: ${{ runner.os }}-ccache-v${{ inputs.cache_version }}-${{ inputs.compiler-id }}-${{ inputs.configuration }}-${{ steps.safe-branch.outputs.name }}
         restore-keys: |
           ${{ runner.os }}-ccache-v${{ inputs.cache_version }}-${{ inputs.compiler-id }}-${{ inputs.configuration }}-${{ inputs.main_branch }}
@@ -169,20 +156,11 @@ runs:
       shell: bash
       run: ccache -s
 
-    - name: Save ccache directory for default branch
-      if: always() && inputs.ccache_enabled == 'true' && steps.safe-branch.outputs.name == inputs.main_branch
+    - name: Save ccache directory
+      if: always() && inputs.ccache_enabled == 'true'
       uses: ./.github/actions/xahau-actions-cache-save
       with:
-        path: ~/.ccache-main
-        key: ${{ runner.os }}-ccache-v${{ inputs.cache_version }}-${{ inputs.compiler-id }}-${{ inputs.configuration }}-${{ inputs.main_branch }}
-        aws-access-key-id: ${{ inputs.aws-access-key-id }}
-        aws-secret-access-key: ${{ inputs.aws-secret-access-key }}
-
-    - name: Save ccache directory for current branch
-      if: always() && inputs.ccache_enabled == 'true' && steps.safe-branch.outputs.name != inputs.main_branch
-      uses: ./.github/actions/xahau-actions-cache-save
-      with:
-        path: ~/.ccache-current
+        path: ~/.ccache
         key: ${{ runner.os }}-ccache-v${{ inputs.cache_version }}-${{ inputs.compiler-id }}-${{ inputs.configuration }}-${{ steps.safe-branch.outputs.name }}
         aws-access-key-id: ${{ inputs.aws-access-key-id }}
         aws-secret-access-key: ${{ inputs.aws-secret-access-key }}

.github/workflows/xahau-ga-nix.yml

@@ -237,7 +237,6 @@ jobs:
           max_size: 2G
           hash_dir: true
           compiler_check: content
-          is_main_branch: ${{ github.ref_name == env.MAIN_BRANCH_NAME }}
 
       - name: Configure Conan
         run: |