feat: add task JSON status update instructions to agents

Add jq commands for agents to update task status lifecycle:
- Step 0: Mark in_progress when starting
- Task Completion: Mark completed when finishing

.claude/agents/code-developer.md

@@ -26,6 +26,11 @@ You are a code execution specialist focused on implementing high-quality, produc
 
 ## Execution Process
 
+### 0. Task Status: Mark In Progress
+```bash
+jq --arg ts "$(date -Iseconds)" '.status="in_progress" | .status_history += [{"from":.status,"to":"in_progress","changed_at":$ts}]' IMPL-X.json > tmp.json && mv tmp.json IMPL-X.json
+```
+
 ### 1. Context Assessment
 **Input Sources**:
 - User-provided task description and context
@@ -368,7 +373,13 @@ function buildCliCommand(task, cliTool, cliPrompt) {
    - All tests pass
    - Functionality works as specified
 
-2. **Update TODO List**: 
+2. **Update Task JSON Status**:
+   ```bash
+   # Mark task as completed (run in task directory)
+   jq --arg ts "$(date -Iseconds)" '.status="completed" | .status_history += [{"from":"in_progress","to":"completed","changed_at":$ts}]' IMPL-X.json > tmp.json && mv tmp.json IMPL-X.json
+   ```
+
+3. **Update TODO List**: 
    - Update TODO_LIST.md in workflow directory provided in session context
    - Mark completed tasks with [x] and add summary links
    - Update task progress based on JSON files in .task/ directory

.claude/agents/test-fix-agent.md

@@ -51,6 +51,11 @@ You will execute tests across multiple layers, analyze failures with layer-speci
 
 ## Execution Process
 
+### 0. Task Status: Mark In Progress
+```bash
+jq --arg ts "$(date -Iseconds)" '.status="in_progress" | .status_history += [{"from":.status,"to":"in_progress","changed_at":$ts}]' IMPL-X.json > tmp.json && mv tmp.json IMPL-X.json
+```
+
 ### Flow Control Execution
 When task JSON contains `flow_control` field, execute preparation and implementation steps systematically.
 
@@ -329,6 +334,13 @@ When generating test results for orchestrator (saved to `.process/test-results.j
 - Pass rate >= 95% + any "high" or "medium" criticality failures → ⚠️ NEEDS FIX (continue iteration)
 - Pass rate < 95% → ❌ FAILED (continue iteration or abort)
 
+## Task Status Update
+
+**Upon task completion**, update task JSON status:
+```bash
+jq --arg ts "$(date -Iseconds)" '.status="completed" | .status_history += [{"from":"in_progress","to":"completed","changed_at":$ts}]' IMPL-X.json > tmp.json && mv tmp.json IMPL-X.json
+```
+
 ## Important Reminders
 
 **ALWAYS:**