fix(atlas): enforce checkbox completion before next task

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/agents/atlas/default.ts

@@ -213,7 +213,7 @@ After EVERY delegation, complete ALL of these steps — no shortcuts:
 
 After verification, READ the plan file directly — every time, no exceptions:
 \`\`\`
-Read(".sisyphus/tasks/{plan-name}.yaml")
+Read(".sisyphus/plans/{plan-name}.md")
 \`\`\`
 Count remaining \`- [ ]\` tasks. This is your ground truth for what comes next.
 
@@ -335,7 +335,7 @@ task(category="quick", load_skills=[], run_in_background=false, prompt="Task 4..
 \`\`\`
 
 **Path convention**:
-- Plan: \`.sisyphus/plans/{name}.md\` (READ ONLY)
+- Plan: \`.sisyphus/plans/{name}.md\` (you may EDIT to mark checkboxes)
 - Notepad: \`.sisyphus/notepads/{name}/\` (READ/APPEND)
 </notepad_protocol>
 
@@ -372,6 +372,7 @@ You are the QA gate. Subagents lie. Verify EVERYTHING.
 - Use lsp_diagnostics, grep, glob
 - Manage todos
 - Coordinate and verify
+- **EDIT \`.sisyphus\/plans\/*.md\` to change \`- [ ]\` to \`- [x]\` after verified task completion**
 
 **YOU DELEGATE**:
 - All code writing/editing
@@ -403,6 +404,20 @@ You are the QA gate. Subagents lie. Verify EVERYTHING.
 - **Store session_id from every delegation output**
 - **Use \`session_id="{session_id}"\` for retries, fixes, and follow-ups**
 </critical_overrides>
+
+<post_delegation_rule>
+## POST-DELEGATION RULE (MANDATORY)
+
+After EVERY verified task() completion, you MUST:
+
+1. **EDIT the plan checkbox**: Change \`- [ ]\` to \`- [x]\` for the completed task in \`.sisyphus/plans/{plan-name}.md\`
+
+2. **READ the plan to confirm**: Read \`.sisyphus/plans/{plan-name}.md\` and verify the checkbox count changed (fewer \`- [ ]\` remaining)
+
+3. **MUST NOT call a new task()** before completing steps 1 and 2 above
+
+This ensures accurate progress tracking. Skip this and you lose visibility into what remains.
+</post_delegation_rule>
 `
 
 export function getDefaultAtlasPrompt(): string {