Replace actions/cache@v5 with local implementation, simplify key inputs

- Remove actions/cache@v5 dependency, implement cache API calls directly
  using curl, tar, and zstd against Gitea's /_apis/artifactcache/ API
- Drop 'key' input, add required 'key-prefix' and 'key-file' inputs
- Cache key is generated as key-prefix-<sha256-of-key-file>
- Update README with revised inputs and Rust-only examples

README.md

@@ -1,40 +1,27 @@
 Cache Action
 ============
 
-A Gitea Action that caches build files under `~/.cache/` using a key file hash. This action uses `actions/cache@v5` under the hood and automatically saves the cache when the job completes successfully.
+A Gitea Action that caches build files under `~/.cache/` using a key file hash. Implements the Gitea artifact cache API directly with curl, tar, and zstd — no external actions required.
 
 ## Inputs
 
 | Input | Description | Required | Default |
 |-------|-------------|----------|---------|
 | `path` | Files/directories to cache | No | `~/.cache/` |
-| `key` | Explicit cache key | No | Auto-generated from hash |
-| `key-file` | File to hash for cache key generation | No | Auto-detects lockfiles |
-| `restore-keys` | Fallback prefix-matched keys | No | `{os}-cache-` |
+| `key-prefix` | Prefix for the cache key | Yes | — |
+| `key-file` | File to hash for the cache key | Yes | — |
+| `restore-keys` | Fallback prefix-matched keys | No | — |
 
 ## Outputs
 
 | Output | Description |
 |--------|-------------|
 | `cache-hit` | `true` if exact key match found, `false` otherwise |
+| `cache-primary-key` | The primary key used for cache lookup |
+| `cache-matched-key` | The key of the cache entry that was restored |
 
 ## Quick Start
 
-### Basic Usage
-
-```yaml
-name: Build with Cache
-on: push
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - uses: Actions/Cache@main
-      - run: echo "Cache restored, proceeding with build..."
-```
-
 ### Rust Example
 
 ```yaml
@@ -52,6 +39,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: Actions/Cache@main
         with:
+          key-prefix: 'rust'
           key-file: 'Cargo.lock'
           path: |
             ~/.cache/
@@ -77,6 +65,7 @@ jobs:
       - uses: Actions/Cache@main
         id: cache
         with:
+          key-prefix: 'rust'
           key-file: 'Cargo.lock'
       - name: Install dependencies
         if: steps.cache.outputs.cache-hit != 'true'
@@ -87,14 +76,11 @@ jobs:
 
 ## How It Works
 
-1. **Cache Key Generation**: If no explicit `key` is provided, the action auto-generates one by:
-   - Hashing the specified `key-file` if provided
-   - Otherwise, hashing all detected lockfiles (package-lock.json, Cargo.lock, go.mod, etc.)
-   - Falls back to hashing all non-git files if no lockfiles found
+1. **Cache Key Generation**: Combines `key-prefix` with the SHA-256 hash of `key-file` (e.g. `rust-<hash>`).
 
-2. **Cache Restore**: Uses `actions/cache@v5` to restore the cache from `~/.cache/`
+2. **Cache Restore**: Calls the Gitea artifact cache API (`/_apis/artifactcache/cache`) to find a matching entry, downloads the archive, and extracts it.
 
-3. **Cache Save**: Automatically saves the cache when the job completes successfully (handled by `actions/cache@v5`)
+3. **Cache Save**: Runs on job completion (`if: always()`), creates a zstd-compressed tar archive, reserves a cache entry via the API, uploads it, and commits it. Skipped if there was a cache hit on the primary key.
 
 ## Cache Scope
 
@@ -102,6 +88,6 @@ The cache is scoped to the key, version, and branch. The default branch cache is
 
 ## Remarks
 
-- Requires Gitea Actions runner version >= 2.327.1 for `actions/cache@v5`
 - The cache server must be enabled on your Gitea instance
+- Requires `curl`, `tar`, and `sha256sum` on the runner (zstd is optional, falls back to gzip)
 - Maximum cache size per repository is 10GB