Urgent Fix: Task Agents Break Plan Mode!

In the realm of coding, few things are as frustrating as a bug that undermines the very foundation of your workflow. Today, we're diving deep into a critical issue: Task Tool Agents bypassing Plan Mode write restrictions. This isn't just a minor annoyance; it's a security and safety vulnerability that needs immediate attention. Let’s get started by understanding the summary of the bug.

Summary

The heart of the matter lies in how agents, when invoked via the Task tool, can write files even when the main assistant is in Plan Mode (activated by shift+tab). This directly violates the core safety guarantee that Plan Mode provides – the prevention of all write operations. Imagine thinking you're in a safe space, carefully planning your next move, only to find out that changes are happening behind the scenes without your explicit consent. This is precisely the problem we're addressing.

Plan Mode is designed to be a sanctuary where you can experiment, strategize, and review potential changes without the risk of accidentally modifying your file system. It's a crucial feature for developers who want to maintain control over their environment and avoid unintended consequences. The fact that Task tool agents can circumvent this safety net is a serious cause for concern.

The implications of this bug are far-reaching. It not only undermines the user's trust in the system but also poses a significant security risk. Unintended file system modifications could lead to data loss, corruption, or even the introduction of malicious code. Therefore, it is imperative to address this issue promptly and comprehensively to restore the integrity of Plan Mode and ensure the safety of user data.

Severity

CRITICAL - This is a security/safety issue that undermines the fundamental purpose of Plan Mode

When we label something as CRITICAL, it's not just a word. It signifies that this bug strikes at the very core of the system's intended functionality. Plan Mode is designed as a safety net, and when that net has a hole, the consequences can be dire. This isn't just about inconvenience; it's about the potential for real damage and loss.

This level of severity demands immediate attention and action. It's not something that can be pushed to the back burner or addressed in a future update. The risk to users is too great, and the potential for harm is too significant. Therefore, this bug needs to be prioritized above all else and resolved as quickly as possible.

Environment

• Claude Code Version: 1.0.71
• Model: claude-opus-4-1-20250805
• Platform: macOS Darwin 24.6.0
• Date: 2025-08-08

Understanding the environment in which a bug occurs is crucial for effective troubleshooting and resolution. In this case, we're dealing with a specific version of Claude Code (1.0.71), a particular model (claude-opus-4-1-20250805), and a specific operating system (macOS Darwin 24.6.0). Knowing these details allows developers to replicate the issue in a controlled environment and pinpoint the exact cause of the problem.

The environment also includes the date on which the bug was observed (2025-08-08). This information can be helpful in identifying any recent changes or updates that may have contributed to the emergence of the bug. By correlating the bug's occurrence with specific environmental factors, developers can narrow down the potential causes and develop targeted solutions. This is also important for tracking the evolution of the bug across different versions and configurations.

Steps to Reproduce

1. Start Claude Code in a directory
2. Enter Plan Mode using shift+tab
3. While in Plan Mode, invoke any agent via the Task tool that has write capabilities (e.g., documentation-specialist)
4. The agent will successfully write files despite Plan Mode being active

To effectively tackle a bug, you need a clear, repeatable process for making it happen. Here's how you can reproduce this Plan Mode bypass:

First, fire up Claude Code in any directory. This sets the stage for the rest of the steps.

Next, engage Plan Mode using the shift+tab shortcut. This is your supposed safe zone, where no writes should occur.

Now, the critical part: while still in Plan Mode, call upon any agent through the Task tool that's capable of writing files. A prime example is the documentation-specialist agent.

Witness the unexpected: The agent will write files, completely ignoring the active Plan Mode. This breach is what we're trying to address.

Expected Behavior

When Plan Mode is active:

• ALL write operations should be blocked
• This should include writes from agents invoked via the Task tool
• Any attempt to write files should fail with an appropriate error message

Here's what we should see when Plan Mode is active:

Absolute Block: ALL write operations, without exception, should be dead in the water. No file creations, no edits – nothing.

Task Tool Included: This block extends to agents triggered via the Task tool. They're not special; they should abide by the same restrictions as everything else.

Clear Error: Any attempt to write should result in a clear, informative error message. Something along the lines of "Write operation blocked in Plan Mode" to make it obvious what's happening.

Actual Behavior

• Plan Mode correctly prevents direct Write/Edit tool usage by the main assistant
• However, agents invoked via Task tool can still write files
• No error or warning is provided about this bypass

What's actually happening is a different story:

Plan Mode does block the main assistant from directly using Write/Edit tools. So, it's partially working.

However, agents summoned through the Task tool can still write files. They're somehow bypassing the restrictions.

To add insult to injury, there's no warning or error message about this bypass. Users are left completely in the dark.

Evidence

Session ID: 12f8749b-798c-4bce-b328-ca957eee43cb Timestamp: 2025-08-08T17:19:40 - 17:20:54

Sequence of events:

1. 17:14:28 - Started working in plan mode (never exited until 17:31)

2. 17:19:40 - Invoked documentation-specialist agent via Task tool:

   {
     "name": "Task",
     "input": {
       "subagent_type": "documentation-specialist",
       "prompt": "Create a detailed implementation roadmap document..."
     }
   }
   

3. 17:20:54 - Agent successfully created file:

   File created successfully at: /Users/user/Desktop/2025-08-08-find-git/IMPLEMENTATION_ROADMAP.md
   

4. 17:31:16 - Finally exited Plan Mode with ExitPlanMode tool

To illustrate this bug, let's walk through a concrete example. We have a session ID (12f8749b-798c-4bce-b328-ca957eee43cb) and a timestamp (2025-08-08T17:19:40 - 17:20:54) that provide a clear timeline of events.

At 17:14:28, the user enters Plan Mode and remains there until 17:31. During this time, at 17:19:40, the user invokes the documentation-specialist agent via the Task tool with a prompt to create a detailed implementation roadmap document. Despite being in Plan Mode, the agent successfully creates a file named IMPLEMENTATION_ROADMAP.md at 17:20:54. This clearly demonstrates the bypass of Plan Mode restrictions by the Task tool agent.

The user finally exits Plan Mode at 17:31:16 using the ExitPlanMode tool, unaware that a file has been created without their explicit consent. This sequence of events provides irrefutable evidence of the bug and its potential impact on user data and security.

Impact

• Security Risk: Plan Mode is meant to be a safety mechanism to prevent unintended file system modifications
• User Trust: Users rely on Plan Mode to review changes before execution
• Data Safety: Unintended writes could modify or overwrite important files

The impact of this bug is far-reaching and potentially devastating. It undermines the very purpose of Plan Mode, which is to provide a safe and controlled environment for users to experiment and strategize without the risk of unintended file system modifications. When Plan Mode fails to prevent write operations, it creates a significant security risk, as malicious code could be introduced or sensitive data could be overwritten without the user's knowledge or consent.

Furthermore, this bug erodes user trust in the system. Users rely on Plan Mode to review changes before execution, ensuring that they have complete control over their file system. When this trust is violated, users may become hesitant to use Plan Mode or even the entire Claude Code platform, fearing that their data is not safe.

The most immediate impact of this bug is on data safety. Unintended writes could modify or overwrite important files, leading to data loss or corruption. This could have serious consequences for users who rely on Claude Code for critical tasks, such as software development, documentation, or research.

Root Cause Analysis

The Task tool appears to spawn agents in a separate context that doesn't inherit the Plan Mode restrictions from the parent session. These child agents have their own tool permissions that aren't constrained by the parent's Plan Mode state.

The root cause of this bug lies in the way the Task tool spawns agents. It seems that these agents are created in a separate context that doesn't inherit the Plan Mode restrictions from the parent session. As a result, these child agents have their own tool permissions that aren't constrained by the parent's Plan Mode state.

This separation of contexts allows the child agents to bypass the Plan Mode restrictions and perform write operations without any hindrance. This is a clear violation of the intended behavior of Plan Mode and poses a significant security risk.

To fix this bug, it is necessary to ensure that all child agents inherit the Plan Mode restrictions from the parent session. This can be achieved by modifying the Task tool to propagate the Plan Mode state to all spawned agents and enforce the same restrictions on their tool permissions.

Suggested Fix

1. Immediate: Task tool should check parent session's Plan Mode state before allowing child agents to perform write operations
2. Comprehensive: All tool invocations (including nested/child agent calls) should respect the Plan Mode state of the root session
3. Safety Check: Add explicit Plan Mode state propagation to all agent invocations

To address this critical bug, we propose a multi-pronged approach that includes immediate and comprehensive fixes, as well as a safety check to prevent future occurrences.

As an immediate solution, the Task tool should be modified to check the parent session's Plan Mode state before allowing child agents to perform write operations. This would prevent the most common scenario where Task-invoked agents bypass Plan Mode restrictions.

For a more comprehensive fix, all tool invocations, including nested or child agent calls, should respect the Plan Mode state of the root session. This would ensure that Plan Mode restrictions are consistently enforced throughout the entire system, regardless of how agents are invoked or nested.

Finally, a safety check should be added to explicitly propagate the Plan Mode state to all agent invocations. This would serve as a safeguard against future bugs or unintended behavior that could compromise the integrity of Plan Mode.

Workaround

Until fixed, users should:

• Avoid using Task tool while in Plan Mode
• Be aware that Plan Mode does NOT currently prevent writes from Task-invoked agents
• Manually verify no unintended files were created after using agents in Plan Mode

Until a proper fix is implemented, users should adopt the following workaround to mitigate the risks associated with this bug:

Avoid using the Task tool while in Plan Mode. This is the most effective way to prevent unintended file system modifications, as it eliminates the possibility of Task-invoked agents bypassing Plan Mode restrictions.

Be aware that Plan Mode does NOT currently prevent writes from Task-invoked agents. This is a critical piece of information that users need to know to avoid complacency and potential data loss.

Manually verify that no unintended files were created after using agents in Plan Mode. This is a necessary step to ensure that no unauthorized modifications have occurred and that your data remains safe.

Additional Context

The file IMPLEMENTATION_ROADMAP.md (13,491 bytes) was created at 10:20 AM while the assistant was in Plan Mode. This file creation was not requested by the user and violated the Plan Mode contract.

To further illustrate the severity of this bug, consider the following example. A file named IMPLEMENTATION_ROADMAP.md (13,491 bytes) was created at 10:20 AM while the assistant was in Plan Mode. This file creation was not requested by the user and directly violated the Plan Mode contract.

This example highlights the potential for unintended file system modifications and the need for immediate action to address this bug. It also underscores the importance of user awareness and the adoption of the recommended workaround until a proper fix is implemented.

Reproducibility

100% - This behavior is consistent and reproducible

The fact that this bug is 100% reproducible means that it is not a random occurrence or a one-off event. It is a consistent and predictable behavior that can be easily replicated by anyone following the steps to reproduce. This makes it easier for developers to identify the root cause of the bug and develop a targeted solution.

It also means that the bug is likely to affect a large number of users, as it is not dependent on specific environmental factors or user behavior. This further underscores the urgency of addressing this bug and implementing a fix as quickly as possible.

Priority

This should be treated as a P0/P1 bug as it compromises the fundamental safety guarantee of Plan Mode.

Given the severity of this bug and its potential impact on user data and security, it should be treated as a P0/P1 bug. This means that it should be given the highest priority and addressed immediately.

A P0 bug is a critical issue that prevents users from using the product or causes data loss. A P1 bug is a major issue that significantly impacts the user experience or causes a security vulnerability. This bug falls into both categories, as it compromises the fundamental safety guarantee of Plan Mode and could lead to data loss or security breaches.

Therefore, it is imperative to allocate the necessary resources and expertise to resolve this bug as quickly as possible. This may involve assigning a dedicated team of developers, conducting thorough testing, and implementing a robust fix that addresses the root cause of the issue.

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Bug report generated after discovering unexpected file creation in Plan Mode session

In conclusion, addressing this bug is essential to restore the integrity of Plan Mode, ensure the safety of user data, and maintain user trust in the Claude Code platform. By following the suggested fix and adopting the recommended workaround, we can mitigate the risks associated with this bug and provide a more secure and reliable experience for our users. To learn more about bug reporting, visit this link.