feat(code): add /clear command to reset conversation history

[littlekirkycode]

Summary

Adds a /clear slash command that wipes conversation history and
reconnects with a fresh session. Useful when context is cluttered or the
agent is stuck in a loop.

Implementation

Client-side command in the message editor — delegates to
SessionService.resetSession():

{
  name: "clear",
  description: "Clear conversation history and start fresh",
  async execute(_args, ctx) {
    const { getSessionService } = await
import("@features/sessions/service/service");
    await getSessionService().resetSession(ctx.taskId, ctx.repoPath);
    toast.success("Conversation cleared");
  },
}

resetSession() calls reconnectInPlace with a new clearHistory
flag. When true, log replay is skipped entirely — the session reconnects
with empty event history instead of replaying from the log file:

const prefetchedLogs = clearHistory
  ? { rawEntries: [], sessionId: undefined, adapter: undefined }
  : await this.fetchSessionLogs(logUrl, taskRunId);

SDK's built-in /clear is suppressed — it doesn't work in our ACP
context, so it's added to UNSUPPORTED_COMMANDS and replaced by our own.

Changes

File	What
commands.ts (message-editor)	New /clear command definition
commands.ts (session)	Add "clear" to UNSUPPORTED_COMMANDS
service.ts	resetSession() passes clearHistory=true, reconnectInPlace skips log fetch when clearing

Test plan

• Type /clear in message editor → conversation history is cleared
• Session reconnects with clean state (no old messages replayed)
• Toast confirms "Conversation cleared"
• /clear appears in slash command autocomplete

[jonathanlab]

Thanks for taking a stab at this! Clearing this way will only clear the in memory logs, but the actual S3 logs will not be reset.
This means that if you run /clear, and then reload the application, you'll see your old logs. (Attachment shows an example of this. I ran /clear after each message, then restarted PostHog Code)

We'll have to create a new task run (Each task run has an associated S3 log) or maybe filter for logs after the /clear command. We already have comparable functionality for this in createNewLocalSession.

[jonathanlab]

nit: no inline imports please

[littlekirkycode]

Your welcome, and thanks for taking the time to provide feedback! Will amend, and stay aware of this in future.

[littlekirkycode]

Both changes applied — removed the inline import and rewrote resetSession() to tear down the old session and create a fresh task run via the suggested createNewLocalSession(), so old messages won't come back after a restart.

Also rebased #1249 on top of this as its clear-and-continue flow goes through resetSession().