fix: cache dir

scan-image/README.md

@@ -23,7 +23,7 @@ You pass a pullable **`image`** reference (e.g. `alpine:3.20` or a digest). Triv
   with:
     image: alpine:3.20
     cache-dir: ${{ steps.db.outputs.cache-dir }}
-    output-dir: ${{ runner.temp }}/trivy-reports
+    output-dir: ${{ github.workspace }}/trivy-reports
     output-file: image.sarif
 - name: Upload report
   uses: actions/upload-artifact@v4
@@ -37,7 +37,7 @@ You pass a pullable **`image`** reference (e.g. `alpine:3.20` or a digest). Triv
 | Input           | Description                                                                 | Required | Default |
 | --------------- | --------------------------------------------------------------------------- | -------- | ------- |
 | `image`         | Image reference to scan (pulled inside the container)                       | Yes      | —       |
-| `cache-dir`     | Trivy cache directory (mounted read-only at `/cache`)                       | No       | `${{ runner.temp }}/trivy` |
+| `cache-dir`     | Trivy cache directory (mounted read-only at `/cache`)                       | No       | `${{ github.workspace }}/.trivy-cache` |
 | `output-dir`    | Host directory for the report (mounted read-write at `/out`)                | Yes      | —       |
 | `output-file`   | SARIF file name only (no `/`); created under `output-dir`                   | Yes      | —       |
 | `trivy-version` | Trivy Docker image (digest pin recommended)                                 | No       | Same pin as `setup-db` / see `action.yaml` |
@@ -52,6 +52,7 @@ You pass a pullable **`image`** reference (e.g. `alpine:3.20` or a digest). Triv
 
 ## Notes
 
-- **`output-dir`** is created with `mkdir -p` if missing; **`cache-dir`** must already exist.
+- Use **`cache-dir`** and **`output-dir`** under **`${{ github.workspace }}`** (or another path the Docker daemon can bind-mount) when the job runs in a container.
+- **`output-dir`** and **`cache-dir`** are created with `mkdir -p` if missing.
 - Local-only images (e.g. built on the host) are not supported unless they are available to the **inner** Docker pull (this action does not mount `docker.sock`).
 - The step still fails if Docker or the container exits non-zero before Trivy completes (e.g. mount or runtime errors).

scan-image/action.yaml

@@ -12,7 +12,7 @@ inputs:
   cache-dir:
     description: "Host path to the Trivy cache directory (mounted read-only at /cache; use the same path as setup-db)"
     required: false
-    default: "${{ runner.temp }}/trivy"
+    default: "${{ github.workspace }}/.trivy-cache"
   output-dir:
     description: "Host directory where the report file is written (mounted read-write at /out)"
     required: true
@@ -43,6 +43,7 @@ runs:
       run: |
         set -euo pipefail
         case "$OUTPUT_FILE" in */*|".."*) echo "FAIL: output-file must be a single file name (no path separators)"; exit 1 ;; esac
+        mkdir -p "$CACHE_DIR_IN"
         cache_dir=$(realpath "$CACHE_DIR_IN")
         mkdir -p "$OUTPUT_DIR_IN"
         output_dir=$(realpath "$OUTPUT_DIR_IN")