fix: tell model to answer general questions directly without tools

The model was using grep to count letters in "strawberry" because the
prompt said "You MUST use tools". Updated system prompts and tool
injection to clarify: only use tools for file/filesystem tasks, answer
general knowledge questions directly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: DaveZheng

src/prompt-trimmer.ts

@@ -74,15 +74,17 @@ function extractUserInstructions(prompt: string): string {
 const SMALL_SYSTEM = `You are a coding assistant. Help the user with software engineering tasks concisely and accurately.
 
 Rules:
-- Use the provided tools to interact with the filesystem
-- Never guess or hallucinate file contents
-- Read files before editing them
-- Keep responses short and focused`;
+- For general knowledge questions, answer directly without using tools.
+- Only use tools when the task involves files or the filesystem.
+- Never guess or hallucinate file contents — use tools to read them.
+- Read files before editing them.
+- Keep responses short and focused.`;
 
 const MEDIUM_SYSTEM = `You are a coding assistant that helps users with software engineering tasks.
 
 Rules:
-- Use the provided tools to interact with the filesystem. Never guess file contents.
+- For general knowledge questions, answer directly without using tools.
+- Only use tools when the task involves files or the filesystem. Never guess file contents.
 - Read files before editing them.
 - Keep responses concise and focused on the task.
 - When editing files, prefer targeted edits over full rewrites.

src/prompt.ts

@@ -30,11 +30,12 @@ export function buildToolInjection(): string {
     "</tool_call>",
     "",
     "CRITICAL RULES:",
-    "- You MUST use tools to interact with the filesystem. NEVER guess or hallucinate file contents.",
+    "- Only use tools when the task involves files, the filesystem, or running commands.",
+    "- For general knowledge questions, answer directly WITHOUT using tools.",
+    "- NEVER guess or hallucinate file contents — use tools to read them.",
     "- Always include the opening <tool_call> tag. Never omit it.",
     "- You may include text before a tool call to explain what you're doing.",
-    "- You may make multiple tool calls in one response.",
-    "- After a tool call, wait for the result before continuing.",
+    "- After a tool call, STOP and wait for the result before continuing.",
     "",
     "<tools>",
     toolsXml,