---
name: workflow-debugging
description: Workflow for issue-based debugging in V8. Use when tasked with debugging a specific issue, usually associated with a Buganizer ID or a specific reproduction script. Do not use for performance regressions.
---

# Workflow: Issue Debugging

Use this skill when tasked with debugging a specific issue, usually associated
with a Buganizer ID or a specific reproduction script. This specializes the
general debugging approach for tracked issues.

## Activation Criteria

- User provides an issue ID or Buganizer URL.
- User provides a reproduction script that crashes or behaves unexpectedly.
- The goal is to find a root cause and propose a fix for a specific bug.

## Core Principles (Inherited & Specialized)

1. **Strict Orchestration**: The main agent acts purely as a dispatcher.
   Delegate technical tasks.
2. **Eager Parallelism**: Initialize Heavy Infrastructure, Conceptual Triage,
   and Static Research in parallel.
3. **Issue Association**: When an issue ID is known, use it to label tests and
   commits.
4. **Handling Inaccessible URLs & Missing Info**:
   - If a URL cannot be accessed directly (e.g., due to authentication), or if
     the intake phase detects that critical attachments (repro script, flags,
     etc.) cannot be accessed or are redacted, the Orchestrator **MUST** stop
     immediately and ask the user to provide them manually.
   - Avoid opening a browser to access the page if it is inaccessible through
     tools.
   - Use separate, sequential interactive prompts (e.g., via `ask_question` or
     direct message to user) to gather missing information:
     - **Input 1**: The JavaScript test source code.
     - **Input 2**: The relevant `d8` flags or command-line arguments.
   - Rely on user-provided reproduction script or flags.
   - If the user denies or does not provide the information, seek explicit
     guidance on how to proceed.
   - Store the test source in the workspace (e.g.,
     `scratch/regress-<issue_id>.js`) to avoid modifying the user's environment
     directly.
5. **Worktree Isolation**: If you debug with a repository in use (e.g., with
   unrelated changes) or debug multiple issues at once you MUST create and
   switch to an isolated git worktree using
   `agents/scripts/create_worktree.sh <issue_id>` BEFORE running any builds or
   tests, to avoid clobbering the main workspace or rebuilding unnecessarily.
6. **Cross-Pollination & Communication**: The Orchestrator MUST actively relay
   relevant discoveries and hypotheses between subagents working on overlapping
   or related tasks to avoid duplicate work and find matching patterns.

## Workflow

### 1. Triage & Parallel Track Initialization

- Analyze the request and extract the Issue ID if available.
- **Worktree Setup**: If an issue ID is identified, immediately create and
  switch to a separate git worktree using
  `agents/scripts/create_worktree.sh <issue_id>` to isolate the investigation.
- **Eager Delegation (MANDATORY)**: The Orchestrator MUST proactively spawn
  subagents to handle all of the following tracks in PARALLEL:
  - **Track A: Heavy Infrastructure**: Spawn a subagent to build `d8` and
    prepare GDB/rr in the worktree.
  - **Track B: Conceptual Triage**: Spawn a subagent to analyze the reproducing
    JS source.
  - **Track C: Static Research**: Spawn a subagent to search for related code
    and spec text, and understand affected areas super deeply.

### 2. Work Branching

- Spawn subagents for independent dimensions (e.g., Spec vs. Runtime).

### 3. Investigation & Escalation

- **Reproduction Verification (MANDATORY)**: Before launching GDB or doing any
  deep debugging, you MUST first execute the reproduction script normally
  (without GDB) using your compiled `d8` binary to verify that the crash indeed
  reproduces locally. This establishes the baseline.
- Use GDB to inspect crash state.
- Escalate unfamiliar concepts immediately.

### 4. Synthesis

- Combine findings to locate the root cause.

### 5. Fix & Verify

- Propose a fix following V8 Best Practices.
- **Create a Regression Test**: Design and implement a clean, semantic
  regression test. This test must be developed and verified to crash/fail on the
  unfixed codebase and pass cleanly on the fixed codebase.
- **Architectural Skepticism (MANDATORY)**: Before presenting the fix, the agent
  MUST explicitly argue *against* its own proposal.
  - *Skepticism Prompt*: "Is this fix too hasty? Does it accidentally disable a
    valid optimization path? Am I fixing a symptom (crashing line) rather than
    the root cause (invariant violation)?"
- **Deep Reasoning**: If the root cause isn't fully understood, spawn a subagent
  to reason deeper about why the failing line exists and what invariant it's
  protecting.
- **Verify**: Confirm with tests and `d8` flags. Run tests on both debug and
  release builds if possible to ensure no assertions are violated and
  performance is not regressed.

### 6. Interactive Review

Before committing or uploading, you MUST present the proposed solution to the
user for review.

- **Present the Diff**: Show the exact code changes proposed.
- **Present the Test**: Show the working regression test file and where it will
  be placed. A bug fix must **always** be accompanied by a working regression
  test. Proposing a fix without a reproducer is strictly forbidden unless the
  user has explicitly waived it.
- **Explain the Root Cause**: Provide a clear explanation of *why* the bug
  happened.
- **Share Skepticism Results**: Briefly mention the counter-arguments considered
  during the Skepticism phase and why the proposed fix is still the right
  choice.
- **Ask for Approval**: Explicitly ask the user if you should proceed with
  committing and uploading.

### 7. Commit & Upload (Specialized)

Once the fix is approved by the user:

- **Issue Association in Commits**:

  - The commit message must follow the V8 convention.
  - It MUST include a `Bug: <issue_id>` line at the bottom.
  - Example Commit Message:
    ```
    [compiler] Fix crash in Turboshaft during loop unrolling

    The loop unroller failed to handle cases where...

    Bug: 12345
    ```

- **Test Naming and Placement**:

  - Name the reproduction test file `regress-<issue_id>.js`.
  - If there is no issue ID, use a descriptive name like
    `regress-short-description.js`.
  - Place the test in the appropriate directory:
    - General regressions: `test/mjsunit/regress/`
    - Component-specific regressions (if applicable): e.g.,
      `test/mjsunit/compiler/regress-12345.js`.
  - Ensure the test file contains a standard header:
    ```javascript
    // Copyright 2026 the V8 project authors. All rights reserved.
    // Use of this source code is governed by a BSD-style license that can be
    // found in the LICENSE file.

    // Flags: --allow-natives-syntax --any-other-flags
    ```

- **Finalization and Upload**:

  - Run `git cl format` to ensure style compliance.
  - Create the commit locally.
  - Follow git-cl rules to upload the change list (CL) to Gerrit.
  - Report the CL URL back to the user/caller if the tool output provides it.
