feat: add mise-config-file option to run-script

### what

add a `mise-config-file` parameter to the `run-script` workflow to load an
additional mise config file, which takes precedence over `mise.toml`

### why

Allow using CI-specific tooling without having `mise` pick it up by default in
the repo

### testing

will test in workflows

### docs

updated docs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: albertodonato

.github/workflows/run-script.yml

@@ -18,6 +18,10 @@ on:
         type: boolean
         description: "Expose the job's read-only GitHub token to the script as GH_TOKEN"
         default: false
+      mise-config-file:
+        type: string
+        description: "Name of an additional mise config file, taking precedence over mise.toml. A bare filename, looked up from the working directory up to the repository root"
+        default: "mise.toml"
     secrets:
       STEP_SECURITY_API_KEY:
         required: false
@@ -29,6 +33,7 @@ jobs:
       contents: read
     env:
       HARDEN_RUNNER: ${{ secrets.STEP_SECURITY_API_KEY != '' }} # zizmor: ignore[secrets-outside-env]
+      MISE_DEFAULT_CONFIG_FILENAME: ${{ inputs.mise-config-file }}
     steps:
       - name: Harden Runner
         if: env.HARDEN_RUNNER == 'true'
@@ -48,6 +53,8 @@ jobs:
         with:
           minimum_release_age: 7d
           cache: true
+          # The default cache key only hashes standard mise config names, so add the custom file.
+          cache_key: "{{cache_key_prefix}}-{{platform}}-{{file_hash}}-${{ hashFiles(format('**/{0}', inputs.mise-config-file)) }}"
 
       # Always read the cache, it's safe to do so even on untrusted PRs.
       - name: Restore pre-commit cache

README.md

@@ -34,6 +34,11 @@ commits never get one, so a SHA is what names the commit you meant.
 
 Run a set of commands on the repository, with the required tools installed via `mise`.
 
+Tools are read from the standard mise config files (`mise.toml`, `.tool-versions`, ...).
+Set `mise-config-file` to load an additional config file, such as one with CI-only
+tools, which takes precedence over `mise.toml`. It must be a bare filename (not a
+path), which mise looks up from the working directory up to the repository root.
+
 
 ```
   Lint: