Feature: Resume most recent session instead of always creating a new one

[clytn3128]

Problem

When opening the OpenCode panel in Obsidian, ensureSessionUrl() always calls createSession(), which creates a new session every time. This means users lose context from their previous conversations and have to manually navigate to their old session.

Proposed Solution

Before creating a new session, query existing sessions via GET /session API and resume the most recently updated one. Only create a new session if no existing sessions are found.

Suggested Implementation

1. Add listSessions() method to the client class

async listSessions() {
  const result = await this.request("GET", "/session");
  const sessions = this.unwrap(result);
  if (!sessions || !Array.isArray(sessions) || sessions.length === 0) {
    return [];
  }
  return sessions.sort((a, b) => {
    const ta = a.updatedAt || a.createdAt || "";
    const tb = b.updatedAt || b.createdAt || "";
    return tb.localeCompare(ta);
  });
}

2. Modify ensureSessionUrl() logic

async ensureSessionUrl(view) {
  if (this.getServerState() !== "running") {
    return;
  }
  const cachedUrl = this.getCachedIframeUrl();
  const existingUrl = cachedUrl != null ? cachedUrl : view.getIframeUrl();
  if (existingUrl && this.client.resolveSessionId(existingUrl)) {
    this.setCachedIframeUrl(existingUrl);
    return;
  }
  let sessionId = null;
  try {
    const sessions = await this.client.listSessions();
    if (sessions.length > 0) {
      sessionId = sessions[0].id;
      console.log("[OpenCode] Resuming existing session:", sessionId);
    }
  } catch (e) {
    console.log("[OpenCode] Could not list sessions, creating new one");
  }
  if (!sessionId) {
    sessionId = await this.client.createSession();
  }
  if (!sessionId) {
    return;
  }
  const sessionUrl = this.client.getSessionUrl(sessionId);
  this.setCachedIframeUrl(sessionUrl);
  view.setIframeUrl(sessionUrl);
  if (this.app.workspace.activeLeaf === view.leaf) {
    await this.contextManager.refreshContextForView(view);
  }
}

Alternative Considerations

• Could add a setting to let users choose between "always new session" and "resume latest session"
• Could add a "New Session" button in the panel header for when users explicitly want a fresh start

I've tested this modification locally and it works well — the panel now resumes the most recent session on startup.