Reduce excessive `any` type usage in ChatInterface.tsx

[KaranJagtiani]

The ChatInterface.tsx component uses any type casts extensively (~30+ instances), which bypasses TypeScript's type safety and can hide bugs. Examples include:

const mapTokenUsage = (raw: any): TokenUsage | undefined => { ... }
(lastMessage as any).segments?.length
(s as any).toolExecution
msgs.map((m: any) => { ... })

Scope

UI (ui/src/components/chat/ChatInterface.tsx):

• Audit all any type usages and replace with proper types.
• Create or extend interfaces in ui/src/types/chat.ts as needed.
• For truly dynamic data (e.g., SSE event payloads), use type guards or runtime validation instead of any casts.
• Focus on the most impactful areas first: message segment handling, tool execution state, and SSE event mapping.

UI (ui/src/types/chat.ts, ui/src/types/events.ts):

• Define proper interfaces for message segments, tool executions, and event payloads.
• Replace annotations?: any with a proper interface.

Acceptance criteria

• Reduce any usage in ChatInterface.tsx completely.
• No TypeScript errors introduced.
• Type guards are used for runtime validation.
• Chat functionality remains unchanged.

How to test manually

1. Run yarn build in the UI directory. There should be no type errors.
2. Run the UI locally (see ui/README.md) and test all chat flows:
   • Sending messages
   • Tool execution and approval
   • Streaming responses
   • Loading chat history
3. Verify no runtime errors in the browser console.

[Aryakoste]

@KaranJagtiani I would like to work on this issue.

[KaranJagtiani]

Sure @Aryakoste

[suyash1567]

Hi, has this issue been abandoned? I would like to have a look at it in that case

[Aryakoste]

Yeah you can work on it

[KaranJagtiani]

The issue is ready to be picked up.