diff --git a/vibn-frontend/app/api/chat/route.ts b/vibn-frontend/app/api/chat/route.ts
index ff6b8c3..47604e0 100644
--- a/vibn-frontend/app/api/chat/route.ts
+++ b/vibn-frontend/app/api/chat/route.ts
@@ -203,7 +203,7 @@ Each project has a persistent \`vibn-dev\` container. Edit files via \`fs_*\` an
 
 **Start a coding session:** \`devcontainer_ensure { projectId }\` (idempotent; first call ~10s, then instant).
 
-**Iterate:**\n- \`shell_exec { projectId, command }\` — anything: \`ls\`, \`npm install\`, \`npm test\`, \`npx create-next-app .\`, \`git status\`. Cwd defaults to \`/workspace\`. Node (LTS), Python 3.12, and Go 1.23 are pre-installed — no setup needed.\n- \`fs_read\` / \`fs_write\` / \`fs_edit { path, oldString, newString }\` (include 2–3 lines of context in \`oldString\` for uniqueness; fails fast if missing or non-unique).\n- \`fs_glob\` / \`fs_grep\` (ripgrep, respects .gitignore) / \`fs_list\` / \`fs_delete\`.\n
+**Iterate:**\n- \`shell_exec { projectId, command }\` — anything: \`ls\`, \`npm install\`, \`npm test\`, \`npx create-next-app .\`, \`git status\`. Cwd defaults to \`/workspace\`. Node (LTS), Python 3.12, and Go 1.23 are pre-installed — no setup needed.\n- \`fs_read\` / \`fs_write\` / \`fs_edit { path, oldString, newString, startLine, endLine }\`. IMPORTANT: For fs_edit, ALWAYS prefer using \`startLine\` and \`endLine\` over \`oldString\`. The Python script requires the start and end lines to be exact. If you use \`oldString\`, you MUST include 2-3 lines of surrounding context for uniqueness, otherwise it fails fast.\n- \`fs_glob\` / \`fs_grep\` (ripgrep, respects .gitignore) / \`fs_list\` / \`fs_delete\`.\n
 
 **Dev servers (preview URL via \`*.preview.vibnai.com\` wildcard):**
 - \`dev_server_start { projectId, command, port: 3000 }\` is a **one-shot** call. It kills old processes on the port, checks the port is free, sets HOST=0.0.0.0 + PORT, launches your command, and returns a clickable \`previewUrl\`. Do NOT pre-flight with \`devcontainer_status\`, \`fs_list\`, \`dev_server_logs\`, or manual \`shell_exec\` kills — the function handles all of that. Just call it. The error tells you what to fix: \`PORT_BUSY\` → pick 3001–3009; \`npm: command not found\` → project needs \`npm install\` first.