feat: integrate Pi backend and Pi Web

pi-web/app/api/sessions/[id]/entries/[entryId]/thinking/route.ts

@@ -0,0 +1,34 @@
+import { NextResponse } from "next/server";
+import { getSessionEntries, resolveSessionPath } from "@/lib/session-reader";
+
+export async function GET(
+  req: Request,
+  { params }: { params: Promise<{ id: string; entryId: string }> },
+) {
+  const { id, entryId } = await params;
+  const blockIndexParam = new URL(req.url).searchParams.get("blockIndex");
+  const blockIndex = blockIndexParam === null ? Number.NaN : Number(blockIndexParam);
+  if (!Number.isSafeInteger(blockIndex) || blockIndex < 0) {
+    return NextResponse.json({ error: "Valid blockIndex is required" }, { status: 400 });
+  }
+
+  try {
+    const filePath = await resolveSessionPath(id);
+    if (!filePath) return NextResponse.json({ error: "Session not found" }, { status: 404 });
+
+    // SessionManager-backed parsing preserves the SDK's malformed-line tolerance.
+    const entry = getSessionEntries(filePath).find((candidate) => candidate.id === entryId);
+    if (!entry || entry.type !== "message" || entry.message.role !== "assistant") {
+      return NextResponse.json({ error: "Assistant message not found" }, { status: 404 });
+    }
+
+    const block = entry.message.content[blockIndex];
+    if (!block || block.type !== "thinking") {
+      return NextResponse.json({ error: "Thinking block not found" }, { status: 404 });
+    }
+
+    return NextResponse.json({ thinking: block.thinking });
+  } catch (error) {
+    return NextResponse.json({ error: String(error) }, { status: 500 });
+  }
+}