perf: improve session, file, and interaction performance

README.md

@@ -8,7 +8,7 @@ Local browser UI for the [pi coding agent](https://github.com/earendil-works/pi)
 
 ## Features
 
-- **Session workspace**: browse, resume, rename, export, and delete conversations grouped by project, with running state, context usage, cost, and compaction details.
+- **Session workspace**: browse, resume, rename, pin, manually order pinned conversations, export, and delete conversations grouped by project, with running state, context usage, cost, and compaction details.
 - **Two ways to branch**: **New session** creates an independent session file from an earlier message; **Edit from here** creates a branch inside the current session.
 - **Project file tools**: browse and upload files, inspect Git diffs, and preview source, Markdown, images, audio, PDFs, and DOCX files with automatic refresh.
 - **Git worktrees**: switch checkouts from the sidebar while keeping sessions from the same repository grouped together.

app/api/agent/[id]/route.ts

@@ -60,12 +60,16 @@ export async function POST(
 
     return NextResponse.json({ success: true, data: result });
   } catch (error) {
+    const message = error instanceof Error ? error.message : String(error);
+    const promptBusy = commandType === "prompt"
+      && !promptAccepted
+      && getRpcSession(id)?.isRunning() === true;
     return NextResponse.json({
-      error: error instanceof Error ? error.message : String(error),
+      error: message,
       ...(commandType === "prompt" && !promptAccepted
-        ? { code: "prompt_rejected", accepted: false }
+        ? { code: promptBusy ? "prompt_busy" : "prompt_rejected", accepted: false }
         : {}),
-    }, { status: 500 });
+    }, { status: promptBusy ? 409 : 500 });
   }
 }
 

app/api/agent/new/route.ts

@@ -65,7 +65,7 @@ export async function POST(req: Request) {
     // in sync so the new cwd is immediately readable via /api/files. Without this,
     // a file request under a brand-new cwd would 403 for up to the cache TTL.
     allowFileRoot(cwd);
-    invalidateSessionListCache();
+    invalidateSessionListCache(session.sessionFile ? [session.sessionFile] : undefined);
 
     const state = await session.send({ type: "get_state" }) as {
       model?: { id: string; provider: string };

app/api/agent/running/route.ts

@@ -1,5 +1,6 @@
 import { NextResponse } from "next/server";
 import { getSessionListVersion } from "@/lib/session-reader";
+import { refreshSessionIndexInBackground } from "@/lib/session-index";
 import {
   getCompletionNotificationSuppressedRpcSessionIds,
   getRunningRpcSessionIds,
@@ -9,6 +10,7 @@ export const dynamic = "force-dynamic";
 
 // GET /api/agent/running - Lightweight snapshot for visible-tab polling.
 export async function GET() {
+  refreshSessionIndexInBackground();
   return NextResponse.json(
     {
       sessionListVersion: getSessionListVersion(),