docs(policy-engine): link to tools reference for tool names and args (google-gemini#22081)

Co-authored-by: Aashir Javed <Aaxhirrr@users.noreply.github.com>
Co-authored-by: Sam Roberts <158088236+g-samroberts@users.noreply.github.com>

Author: Aaxhirrr

docs/reference/policy-engine.md

@@ -71,7 +71,9 @@ primary conditions are the tool's name and its arguments.
 
 #### Tool Name
 
-The `toolName` in the rule must match the name of the tool being called.
+The `toolName` in the rule must match the name of the tool being called. For a
+complete list of built-in tool names, see the
+[Tools reference](/docs/reference/tools#available-tools).
 
 - **Wildcards**: You can use wildcards to match multiple tools.
   - `*`: Matches **any tool** (built-in or MCP).
@@ -87,7 +89,9 @@ The `toolName` in the rule must match the name of the tool being called.
 
 If `argsPattern` is specified, the tool's arguments are converted to a stable
 JSON string, which is then tested against the provided regular expression. If
-the arguments don't match the pattern, the rule does not apply.
+the arguments don't match the pattern, the rule does not apply. For a list of
+argument keys available for each tool, see the **Parameters** in the
+[Tools reference](/docs/reference/tools#available-tools).
 
 #### Execution environment
 
@@ -279,7 +283,11 @@ directory are **ignored**.
 
 ### TOML rule schema
 
-Here is a breakdown of the fields available in a TOML policy rule:
+This section describes the fields available in a TOML policy rule.
+
+For valid built-in `toolName` values and their argument structures (used by
+`argsPattern`), see the
+[Tools reference](/docs/reference/tools#available-tools).
 
 ```toml
 [[rule]]
@@ -365,6 +373,9 @@ priority = 10
 
 To simplify writing policies for `run_shell_command`, you can use
 `commandPrefix` or `commandRegex` instead of the more complex `argsPattern`.
+These are policy-rule shorthands, not arguments of the `run_shell_command` tool
+itself. For the tool's invocation arguments, see [Shell tool](/docs/tools/shell)
+and [Tools reference](/docs/reference/tools#available-tools).
 
 - `commandPrefix`: Matches if the `command` argument starts with the given
   string.