feat: expose existing hook registry capabilities to extensions

[SiegristJ]

This PR enables extensions to utilize the existing Hook System by exposing the hooks configuration field in ExtensionConfig and passing it through the ExtensionManager.

Context
The HookRegistry (in core/src/hooks/hookRegistry.ts) already contains logic to load hooks from extensions:

1 // Existing logic in HookRegistry.ts
2 const extensions = this.config.getExtensions() || [];
3 for (const extension of extensions) {
4 if (extension.isActive && extension.hooks) {
5 // logic to register hooks
6 }
7 }

However, extensions were unable to actually use this feature because:

1. The ExtensionConfig interface (in cli/src/config/extension.ts) was missing the hooks definition.
2. The ExtensionManager (in cli/src/config/extension-manager.ts) was not passing the hooks field from the loaded JSON to the runtime extension object.

Changes

• packages/cli/src/config/extension.ts: Added optional hooks field to ExtensionConfig interface, importing HookDefinition and HookEventName from core.
• packages/cli/src/config/extension-manager.ts: Updated loadExtension to assign hooks: config.hooks when initializing the extension object.

Impact
This change transforms extensions from static tool providers into capable agent interceptors. It unblocks critical enterprise use cases such as:

• Custom Memory Systems: Capturing AfterAgent events to store history and BeforeModel events to inject context (e.g., RAG, Episodic Memory).
• Safety & Compliance: Implementing PII scrubbing or policy checks via BeforeModel or BeforeTool hooks.
• Audit Logging: Recording comprehensive session activity to external systems.

Verification
Verified locally by building the CLI and loading a test extension with BeforeModel and AfterAgent hooks. Confirmed that the HookRegistry correctly identified and registered the hooks from the extension's
gemini-extension.json

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[gemini-code-assist]

Summary of Changes

Hello @SiegristJ, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the capabilities of extensions by integrating them with the core Hook System. It addresses previous limitations where extensions could not leverage hooks due to missing configuration definitions and data passing mechanisms. By modifying the ExtensionConfig interface and the ExtensionManager, extensions can now define and register custom hooks, enabling them to intercept and influence various application events, thereby unlocking advanced functionalities for enterprise use cases.

Highlights

• Hook System Integration: Extensions can now utilize the existing Hook System by exposing the hooks configuration field in ExtensionConfig.
• Configuration Update: The ExtensionConfig interface has been updated to include an optional hooks definition, importing necessary types from the core library.
• Extension Manager Enhancement: The ExtensionManager is now updated to correctly pass the hooks field from the loaded JSON configuration to the runtime extension object.
• Enabling Advanced Use Cases: This change unblocks critical enterprise use cases such as custom memory systems, safety and compliance features, and comprehensive audit logging through extension-defined hooks.

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[gemini-code-assist]

Code Review

This pull request successfully exposes the hook system to extensions by adding the hooks configuration field. The changes are straightforward. However, I've identified a critical security concern: the installation consent flow does not inform the user that an extension can execute arbitrary commands via hooks. My review includes a comment with details on how to address this to ensure users are aware of the capabilities they are granting to an extension.

[gemini-code-assist]

The introduction of hooks allows extensions to execute arbitrary commands on the user's machine (via HookType.Command), which is a significant security-sensitive capability. The user should be explicitly informed about this during the installation consent flow.

Currently, the extensionConsentString function in packages/cli/src/config/extensions/consent.ts does not account for the hooks property. Please update the consent mechanism to inform the user if an extension uses hooks, for example by listing which events it hooks into.