feat(commands): Enable @file processing in TOML commands (#6716)

docs/cli/commands.md

@@ -271,7 +271,7 @@ When a custom command attempts to execute a shell command, Gemini CLI will now p
 
 1.  **Inject Commands:** Use the `!{...}` syntax.
 2.  **Argument Substitution:** If `{{args}}` is present inside the block, it is automatically shell-escaped (see [Context-Aware Injection](#1-context-aware-injection-with-args) above).
-3.  **Robust Parsing:** The parser correctly handles complex shell commands that include nested braces, such as JSON payloads.
+3.  **Robust Parsing:** The parser correctly handles complex shell commands that include nested braces, such as JSON payloads. **Note:** The content inside `!{...}` must have balanced braces (`{` and `}`). If you need to execute a command containing unbalanced braces, consider wrapping it in an external script file and calling the script within the `!{...}` block.
 4.  **Security Check and Confirmation:** The CLI performs a security check on the final, resolved command (after arguments are escaped and substituted). A dialog will appear showing the exact command(s) to be executed.
 5.  **Execution and Error Reporting:** The command is executed. If the command fails, the output injected into the prompt will include the error messages (stderr) followed by a status line, e.g., `[Shell command exited with code 1]`. This helps the model understand the context of the failure.
 
@@ -299,6 +299,41 @@ Please generate a Conventional Commit message based on the following git diff:
 
 When you run `/git:commit`, the CLI first executes `git diff --staged`, then replaces `!{git diff --staged}` with the output of that command before sending the final, complete prompt to the model.
 
+##### 4. Injecting File Content with `@{...}`
+
+You can directly embed the content of a file or a directory listing into your prompt using the `@{...}` syntax. This is useful for creating commands that operate on specific files.
+
+**How It Works:**
+
+- **File Injection**: `@{path/to/file.txt}` is replaced by the content of `file.txt`.
+- **Multimodal Support**: If the path points to a supported image (e.g., PNG, JPEG), PDF, audio, or video file, it will be correctly encoded and injected as multimodal input. Other binary files are handled gracefully and skipped.
+- **Directory Listing**: `@{path/to/dir}` is traversed and each file present within the directory and all subdirectories are inserted into the prompt. This respects `.gitignore` and `.geminiignore` if enabled.
+- **Workspace-Aware**: The command searches for the path in the current directory and any other workspace directories. Absolute paths are allowed if they are within the workspace.
+- **Processing Order**: File content injection with `@{...}` is processed _before_ shell commands (`!{...}`) and argument substitution (`{{args}}`).
+- **Parsing**: The parser requires the content inside `@{...}` (the path) to have balanced braces (`{` and `}`).
+
+**Example (`review.toml`):**
+
+This command injects the content of a _fixed_ best practices file (`docs/best-practices.md`) and uses the user's arguments to provide context for the review.
+
+```toml
+# In: <project>/.gemini/commands/review.toml
+# Invoked via: /review FileCommandLoader.ts
+
+description = "Reviews the provided context using a best practice guide."
+prompt = """
+You are an expert code reviewer.
+
+Your task is to review {{args}}.
+
+Use the following best practices when providing your review:
+
+@{docs/best-practices.md}
+"""
+```
+
+When you run `/review FileCommandLoader.ts`, the `@{docs/best-practices.md}` placeholder is replaced by the content of that file, and `{{args}}` is replaced by the text you provided, before the final prompt is sent to the model.
+
 ---
 
 #### Example: A "Pure Function" Refactoring Command