Feature Request: Programmatic access to Agent Threads / sending messages to active sessions

[cellulosa]

Body

What are you proposing?

Expose an API for extensions and/or external tooling to interact with existing Agent Threads.

At a minimum, it would be useful to support:

• Listing active agent threads/sessions
• Sending a user message to an existing thread (shell + agent)

Why does this matter?

I'm using Claude Agent inside Zed and often have multiple active agent threads running simultaneously.

I'd like to build small automation workflows around them, such as:

• /continue-all
• /schedule-continue 14:20
• Automatically sending follow-up prompts to active agent sessions

Currently, it appears that agent sessions are managed internally through claude-agent-acp, but I couldn't find a supported way for extensions or external tools to interact with existing sessions.

Exposing thread/message APIs would unlock scheduling, orchestration, automation, and multi-agent workflows.

Are there any examples or context?

A simple example would be scheduling a message like:

text continue

to all active Claude Agent threads at a specific time.

Another example would be extensions that coordinate multiple running agent sessions, monitor them, or automate repetitive follow-up interactions.

Possible approach

Some possible APIs could be:

ts zed.agent.listThreads() zed.agent.sendMessage(threadId, "continue")

or command-based equivalents that extensions can invoke.

Even a limited API that allows:

• enumerating active threads
• sending a user message to a thread

would enable a wide range of automation use cases without requiring direct access to the underlying ACP runtime.

Related discussions:

• Concurrent Agent Chat Windows (tabbed agent threads) #42381 Concurrent Agent Chat Windows (mentions thread/session management)
• ACP discussion: "Add chat history method to continue previous agents chat created in different client"

My request is slightly different: I'm specifically asking whether extensions or external tools can enumerate active agent threads and send messages to existing sessions programmatically.

[jutaz]

Opened a PR #62060 which adds support for sending messages to an agent thread.