chore(docs): Better explanation on how to allow tools in external directories (#10862)

packages/web/src/content/docs/permissions.mdx

@@ -80,12 +80,49 @@ Permission patterns use simple wildcard matching:
 
 ### Home Directory Expansion
 
-You can use `~` or `$HOME` at the start of a pattern to reference your home directory. This is particularly useful for `external_directory` rules.
+You can use `~` or `$HOME` at the start of a pattern to reference your home directory. This is particularly useful for [`external_directory`](#external-directories) rules.
 
 - `~/projects/*` -> `/Users/username/projects/*`
 - `$HOME/projects/*` -> `/Users/username/projects/*`
 - `~` -> `/Users/username`
 
+### External Directories
+
+Use `external_directory` to allow tool calls that touch paths outside the working directory where OpenCode was started. This applies to any tool that takes a path as input (for example `read`, `edit`, `list`, `glob`, `grep`, and many `bash` commands).
+
+Home expansion (like `~/...`) only affects how a pattern is written. It does not make an external path part of the current workspace, so paths outside the working directory must still be allowed via `external_directory`.
+
+For example, this allows access to everything under `~/projects/personal/`:
+
+```json title="opencode.json"
+{
+  "$schema": "https://opencode.ai/config.json",
+  "permission": {
+    "external_directory": {
+      "~/projects/personal/**": "allow"
+    }
+  }
+}
+```
+
+Any directory allowed here inherits the same defaults as the current workspace. Since [`read` defaults to `allow`](#defaults), reads are also allowed for entries under `external_directory` unless overridden. Add explicit rules when a tool should be restricted in these paths, such as blocking edits while keeping reads:
+
+```json title="opencode.json"
+{
+  "$schema": "https://opencode.ai/config.json",
+  "permission": {
+    "external_directory": {
+      "~/projects/personal/**": "allow"
+    },
+    "edit": {
+      "~/projects/personal/**": "deny"
+    }
+  }
+}
+```
+
+Keep the list focused on trusted paths, and layer extra allow or deny rules as needed for other tools (for example `bash`).
+
 ---
 
 ## Available Permissions