diff --git a/navi/core/agent.py b/navi/core/agent.py
index 194b789..4363c7e 100644
--- a/navi/core/agent.py
+++ b/navi/core/agent.py
@@ -199,6 +199,31 @@
         return frozenset()
 
 
+def _todo_progress_message(session_id: str, *, first_iteration: bool = False) -> "Message | None":
+    """Build a compact system reminder with current todo state and update discipline."""
+    try:
+        from navi.tools.todo import _plans, _STATUS_ICON
+        tasks = _plans.get(session_id, [])
+        if not tasks:
+            return None
+
+        lines = ["[Todo discipline]"]
+        if first_iteration:
+            lines.append("The todo list was auto-populated from the plan.")
+        lines.append("Use 1-based todo indexes. When starting a step, mark it in_progress.")
+        lines.append("After completing or failing a step, update todo before moving on.")
+        lines.append("Do not mark a step done until you have verified it; include validation explaining the check.")
+        lines.append("Before final response, close every completed step with todo update and validation.")
+        lines.append("Current todo:")
+        for i, t in enumerate(tasks, 1):
+            icon = _STATUS_ICON.get(t.status, "?")
+            validation_note = f"; verified: {t.validation}" if t.validation else ""
+            lines.append(f"  {icon} {i}. {t.text} ({t.status}{validation_note})")
+        return Message(role="system", content="\n".join(lines))
+    except Exception:
+        return None
+
+
 class Agent:
     def __init__(
         self,
@@ -650,19 +675,9 @@
             ):
                 built_ctx.append(self._build_goal_anchor(session_id, user_message))
 
-            if iteration == 0:
-                try:
-                    from navi.tools.todo import _plans, _STATUS_ICON
-                    tasks = _plans.get(session_id, [])
-                    if tasks:
-                        lines = ["[Todo — track your progress]"]
-                        for i, t in enumerate(tasks):
-                            icon = _STATUS_ICON.get(t.status, "?")
-                            lines.append(f"  {icon} [{i}] {t.text} ({t.status})")
-                        lines.append("Mark each step in_progress when you start it, done when complete.")
-                        built_ctx.append(Message(role="system", content="\n".join(lines)))
-                except Exception:
-                    pass
+            todo_msg = _todo_progress_message(session_id, first_iteration=(iteration == 0))
+            if todo_msg:
+                built_ctx.append(todo_msg)
 
             # Snapshot todo state before this iteration (for stall detection after)
             _todo_snapshot_before = _todo_status_snapshot(session_id)
@@ -887,9 +902,9 @@
                     )
                     _replan_msg = (
                         f"[Adaptive re-plan] {failed_labels} just failed. "
-                        "Before continuing, revise your plan: call todo(op=\"set\") or todo(op=\"update\") "
-                        "to replace or skip the remaining pending steps with a revised approach "
-                        "that accounts for what went wrong. Then continue execution."
+                        "Before continuing, revise your plan with the todo tool: either replace the remaining "
+                        "pending steps or mark failed/skipped steps with validation. Then continue execution "
+                        "with an approach that accounts for what went wrong."
                     )
                     log.info("agent.adaptive_replan_queued", failures=len(new_failures),
                              session_id=session_id)
@@ -1439,6 +1454,8 @@
             pass
 
         lines.append("Stay on track — complete the remaining pending/in_progress steps.")
+        lines.append("Use 1-based todo indexes. Mark completed steps done only after verification, with validation.")
+        lines.append("Before final response, update todo for every completed step, including the final one.")
         return Message(role="system", content="\n".join(lines))
 
     def _tool_list(self, enabled: list[str]) -> list[Tool]:
diff --git a/navi/tools/todo.py b/navi/tools/todo.py
index 42d4fdf..eeb1675 100644
--- a/navi/tools/todo.py
+++ b/navi/tools/todo.py
@@ -29,9 +29,11 @@
     description = (
         "Task plan tracker. Your todo list is automatically populated from the plan at the start of each task — "
         "you do NOT need to call 'set'. "
-        "Call 'update' (index + status) immediately after completing or failing each step — before moving to the next. "
+        "Indexes are 1-based. Call 'update' with status='in_progress' when you start a step. "
+        "Call 'update' immediately after completing or failing each step — before moving to the next. "
         "When marking a step 'done', you MUST provide a 'validation' field describing how you verified the result. "
         "When marking a step 'failed', provide 'validation' explaining what went wrong and what you tried. "
+        "Before final response, make sure every completed step, including the final step, is marked done with validation. "
         "Call 'view' to re-orient yourself after sub-agent execution or long tool chains. "
         "Use 'set' only when you need to replace the plan mid-task (rare). "
         "Statuses: pending → in_progress → done / failed / skipped."