feat(refactor): live zed-style codebase files autocomplete and context attachment

vibn-frontend/app/api/chat/route.ts

@@ -30,6 +30,7 @@ import {
 } from "@/lib/dev-container-git";
 import { buildDesignKitPromptSection } from "@/lib/design-kits/for-ai";
 import { buildCodebaseSummary } from "@/lib/ai/codebase-summary";
+import { execInDevContainer } from "@/lib/dev-container";
 import type { ChatMessage, ToolCall } from "@/lib/ai/gemini-chat";
 
 // C-01: Lowered from 15 → 8. Real workflows (scaffold → install →
@@ -404,6 +405,7 @@ export async function POST(request: Request) {
     workspace: string;
     mcp_token?: string;
     chatMode?: "vibe" | "collaborate" | "delegate";
+    attachedFiles?: string[];
   };
   try {
     body = await request.json();
@@ -411,7 +413,14 @@ export async function POST(request: Request) {
     return NextResponse.json({ error: "Invalid JSON" }, { status: 400 });
   }
 
-  const { thread_id, message, workspace, mcp_token, chatMode = "vibe" } = body;
+  const {
+    thread_id,
+    message,
+    workspace,
+    mcp_token,
+    chatMode = "vibe",
+    attachedFiles = [],
+  } = body;
   if (!thread_id || !message?.trim()) {
     return NextResponse.json(
       { error: "thread_id and message are required" },
@@ -529,6 +538,32 @@ export async function POST(request: Request) {
     chatMode,
   );
 
+  let fileContextsBlock = "";
+  if (
+    Array.isArray(attachedFiles) &&
+    attachedFiles.length > 0 &&
+    activeProject?.slug
+  ) {
+    fileContextsBlock =
+      "\n\n=== USER-ATTACHED CODE CONTEXT ===\nThe user has explicitly attached the following files to this conversation turn as active context. You MUST refer to these file states when writing your response or deciding edits:\n";
+    for (const f of attachedFiles) {
+      const safePath = String(f).replace(/\.\./g, "").replace(/^\//, "");
+      try {
+        const res = (await execInDevContainer({
+          projectId: activeProject.id,
+          command: `cat "/workspace/${activeProject.slug}/${safePath}" 2>/dev/null || echo "[File not found]"`,
+        })) as unknown as { exitCode: number; stdout: string };
+        fileContextsBlock += `\nFile: \`${safePath}\`\n\`\`\`\n${res.stdout}\n\`\`\`\n`;
+      } catch {
+        fileContextsBlock += `\nFile: \`${safePath}\`\n[Error reading file]\n`;
+      }
+    }
+  }
+
+  if (fileContextsBlock) {
+    systemPrompt += fileContextsBlock;
+  }
+
   // Sentry-as-product Stage 4: auto-surface unresolved errors at
   // chat-turn start. We pull the last 6 hours' unresolved issues
   // for the active project; if anything has fired ≥2 times, we