feat: add rule to capture user messages mid-task

When the user sends a message while Claude is "churning" (executing
multiple tool calls), those messages must be immediately added to
TodoWrite. The user cannot see Claude's output during tool execution,
so their messages may be forgotten if not tracked as todos.

Author: nsheaps

.ai/rules/todo-management.md

@@ -49,3 +49,37 @@ Simple conversational responses that don't use tools are exempt. Everything else
 2. Start using tools immediately
 3. Maybe update todos later (or forget)
 ```
+
+## Rule: Capture User Messages Mid-Task
+
+**CRITICAL:** When the user sends a message while you are "churning" (executing multiple tool calls), you MUST immediately add it to your TodoWrite.
+
+### Why This Matters
+
+The user cannot see your output while you're in the middle of tool execution. Their messages may contain:
+- Corrections to what you're doing
+- New requirements
+- Questions that need answers
+- Feedback on your approach
+
+If you don't capture these as todos, you will forget them or fail to address them.
+
+### Correct Pattern
+
+```
+1. You're mid-task, executing tools
+2. User sends a message (appears as system-reminder)
+3. IMMEDIATELY add a todo: "Address user message: <summary>"
+4. Continue current work OR pivot based on urgency
+5. Address the todo before considering work complete
+```
+
+### Incorrect Pattern
+
+```
+1. You're mid-task, executing tools
+2. User sends a message
+3. You see it but keep working
+4. You forget to address it
+5. User gets frustrated
+```