feat (coding-agent): Expose getToolDefinition to command context

[xl0]

I've seen more than enough tools and mcp servers where the author clearly never reviewed the actual output of those tools.

I made a /tool command extension that lets you call the agent tools manually. It does not add the calls to the context, just adds a nice ui to fill in the input schema and displays the tool output mostly raw - no custom rendering.

Peek.2026-05-24.12-30.mp4

Right now we actually don't have a way to grab the tool definitions from a command context. We have getAllTools that resurns ToolInfo[]:

export type ToolInfo = Pick<ToolDefinition, "name" | "description" | "parameters"> & {
	sourceInfo: SourceInfo;
};

which picks out just a few items from the ToolDefinition.

This PR just adds a getToolDefinition to the command context, which calls the AgentSession getToolDefinition and wraps the output in ReadOnly as a hint. Not married to the implementation. Maybe we could just expose the AgentSession to the commands and tools?

P.S.
Also a somewhat unrelated

export { convertToPng } from "./utils/image-convert.ts";