extension_host: Load granted extension capabilities from settings (#39472)

This PR adds the ability to control the capabilities granted to
extensions by the extension host via the new
`granted_extension_capabilities` setting.

This setting is a list of the capabilities granted to any extension
running in Zed.

The currently available capabilities are:

- `process:exec` - Grants extensions the ability to invoke commands
using
[`zed_extension_api::process::Command`](https://docs.rs/zed_extension_api/latest/zed_extension_api/process/struct.Command.html)
- `download_file` - Grants extensions the ability to download files
using
[`zed_extension_api::download_file`](https://docs.rs/zed_extension_api/latest/zed_extension_api/fn.download_file.html)
- `npm:install` - Grants extensions the ability to install npm packages
using
[`zed_extension_api::npm_install_package`](https://docs.rs/zed_extension_api/latest/zed_extension_api/fn.npm_install_package.html)

Each of these capabilities has parameters that can be used to customize
the permissions.

For instance, to only allow downloads from GitHub, the `download_file`
capability can specify an allowed `host`:

```json
[
  { "kind": "download_file", "host": "github.com", "path": ["**"] }
]
```

The same capability can also be granted multiple times with different
parameters to build up an allowlist:

```json
[
  { "kind": "download_file", "host": "github.com", "path": ["**"] },
  { "kind": "download_file", "host": "gitlab.com", "path": ["**"] }
]
```

When an extension is not granted a capability, the associated extension
APIs protected by that capability will fail.

For instance, trying to use `zed_extension_api::download_file` when the
`download_file` capability is not granted will result in an error that
will be surfaced by the extension:

```
Language server phpactor:

from extension "PHP" version 0.4.3: failed to download file: capability for download_file https://github.com/phpactor/phpactor/releases/download/2025.07.25.0/phpactor.phar is not granted by the extension host
```

Release Notes:

- Added a `granted_extension_capabilities` setting to control the
capabilities granted to extensions.

crates/settings/src/settings_content.rs

@@ -1,5 +1,6 @@
 mod agent;
 mod editor;
+mod extension;
 mod language;
 mod language_model;
 mod project;
@@ -9,6 +10,7 @@ mod workspace;
 
 pub use agent::*;
 pub use editor::*;
+pub use extension::*;
 pub use language::*;
 pub use language_model::*;
 pub use project::*;
@@ -433,21 +435,6 @@ pub struct CallSettingsContent {
     pub share_on_join: Option<bool>,
 }
 
-#[skip_serializing_none]
-#[derive(Deserialize, Serialize, PartialEq, Debug, Default, Clone, JsonSchema, MergeFrom)]
-pub struct ExtensionSettingsContent {
-    /// The extensions that should be automatically installed by Zed.
-    ///
-    /// This is used to make functionality provided by extensions (e.g., language support)
-    /// available out-of-the-box.
-    ///
-    /// Default: { "html": true }
-    #[serde(default)]
-    pub auto_install_extensions: HashMap<Arc<str>, bool>,
-    #[serde(default)]
-    pub auto_update_extensions: HashMap<Arc<str>, bool>,
-}
-
 #[skip_serializing_none]
 #[derive(Clone, PartialEq, Default, Serialize, Deserialize, JsonSchema, MergeFrom, Debug)]
 pub struct GitPanelSettingsContent {

crates/settings/src/settings_content/extension.rs

@@ -0,0 +1,59 @@
+use std::sync::Arc;
+
+use collections::HashMap;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use serde_with::skip_serializing_none;
+use settings_macros::MergeFrom;
+
+#[skip_serializing_none]
+#[derive(Debug, PartialEq, Clone, Default, Serialize, Deserialize, JsonSchema, MergeFrom)]
+pub struct ExtensionSettingsContent {
+    /// The extensions that should be automatically installed by Zed.
+    ///
+    /// This is used to make functionality provided by extensions (e.g., language support)
+    /// available out-of-the-box.
+    ///
+    /// Default: { "html": true }
+    #[serde(default)]
+    pub auto_install_extensions: HashMap<Arc<str>, bool>,
+    #[serde(default)]
+    pub auto_update_extensions: HashMap<Arc<str>, bool>,
+    /// The capabilities granted to extensions.
+    #[serde(default)]
+    pub granted_extension_capabilities: Option<Vec<ExtensionCapabilityContent>>,
+}
+
+/// A capability for an extension.
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, JsonSchema)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum ExtensionCapabilityContent {
+    #[serde(rename = "process:exec")]
+    ProcessExec(ProcessExecCapabilityContent),
+    DownloadFile(DownloadFileCapabilityContent),
+    #[serde(rename = "npm:install")]
+    NpmInstallPackage(NpmInstallPackageCapabilityContent),
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub struct ProcessExecCapabilityContent {
+    /// The command to execute.
+    pub command: String,
+    /// The arguments to pass to the command. Use `*` for a single wildcard argument.
+    /// If the last element is `**`, then any trailing arguments are allowed.
+    pub args: Vec<String>,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub struct DownloadFileCapabilityContent {
+    pub host: String,
+    pub path: Vec<String>,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub struct NpmInstallPackageCapabilityContent {
+    pub package: String,
+}