Simplify to local tar.xz filesystem cache, remove API dependency

- Store cache as tar.xz archives on runner filesystem at ~/.cache/.cache-store/
- No external API calls, no node.js, no curl needed
- Restore extracts archive if key matches, save creates one on miss
- Drastically simpler and more reliable for self-hosted runners

README.md

@@ -1,28 +1,29 @@
 Cache Action
 ============
 
-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.
+A Gitea Action that caches build files as `tar.xz` archives on the runner filesystem. Simple, fast, no external dependencies.
 
 ## Inputs
 
 | Input | Description | Required | Default |
 |-------|-------------|----------|---------|
-| `path` | Files/directories to cache | No | `~/.cache/` |
+| `path` | Directory to cache | No | `~/.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
+## How It Works
 
-### Rust Example
+1. Hashes `key-file` with SHA-256, combines with `key-prefix` as the cache key
+2. Stores archives at `~/.cache/.cache-store/<key>.tar.xz`
+3. Restores by extracting the archive, saves by creating one
+
+## Rust Example
 
 ```yaml
 name: Rust Build
@@ -42,16 +43,14 @@ jobs:
           key-prefix: 'rust'
           key-file: 'Cargo.lock'
           path: |
-            ~/.cache/
             ~/.cargo/registry
             ~/.cargo/git
             target
       - name: Build
-        run: |
-          cargo build --release
+        run: cargo build --release
 ```
 
-### Skip Steps on Cache Hit
+## Skip Steps on Cache Hit
 
 ```yaml
 name: Build with Conditional Steps
@@ -67,27 +66,9 @@ jobs:
         with:
           key-prefix: 'rust'
           key-file: 'Cargo.lock'
-      - name: Install dependencies
+      - name: Fetch dependencies
         if: steps.cache.outputs.cache-hit != 'true'
         run: cargo fetch
       - name: Build
         run: cargo build --release
 ```
-
-## How It Works
-
-1. **Cache Key Generation**: Combines `key-prefix` with the SHA-256 hash of `key-file` (e.g. `rust-<hash>`).
-
-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**: 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
-
-The cache is scoped to the key, version, and branch. The default branch cache is available to other branches.
-
-## Remarks
-
-- 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