chore: Replace OnSnapshot callback with Emitter interface

[johnstcn]

• Add Emitter interface to screentracker package
• Remove OnSnapshot from PTYConversationConfig, accept Emitter in NewPTY
• Rename EventEmitter methods: EmitMessages, EmitStatus, EmitScreen
• Accept agentType at NewEventEmitter construction instead of per-call
• Update server.go wiring, all tests pass

Created using Mux (Opus 4.5)

[github-actions]

✅ Preview binaries are ready!

To test with modules: agentapi_version = "agentapi_185" or download from: https://github.com/coder/agentapi/releases/tag/agentapi_185

[Copilot]

Pull request overview

This PR refactors how PTY conversation snapshot updates are propagated by replacing the OnSnapshot callback with a screentracker.Emitter interface, and wires the HTTP API event stream through that interface.

Changes:

• Introduces screentracker.Emitter and updates PTYConversation to emit status/messages/screen via the interface.
• Refactors httpapi.EventEmitter to use a functional-options constructor and renames update methods to Emit*.
• Updates server wiring and tests to pass an emitter into st.NewPTY.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
lib/screentracker/conversation.go	Adds the Emitter interface to represent conversation state emission.
lib/screentracker/pty_conversation.go	Removes OnSnapshot callback and emits via Emitter; updates NewPTY signature.
lib/screentracker/pty_conversation_test.go	Updates tests to pass a stub emitter into NewPTY.
lib/httpapi/events.go	Refactors EventEmitter construction to options + renames methods to Emit*.
lib/httpapi/server.go	Passes EventEmitter directly to st.NewPTY as an Emitter.
lib/httpapi/events_test.go	Updates tests for NewEventEmitter options and Emit* method names.

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[35C4n0r]

LGTM!