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Release v0.2.0: Comprehensive Web App Debugging Support (#1)
* feat: Enhance security and optimize performance This commit introduces several security and optimization enhancements to the MCP server. Security: - Disabled the `run_in_terminal` function to prevent arbitrary code execution. - Added path traversal protection to the `read_text_file` function. - Sanitized input for the `run_tests_json` function to prevent command injection. Optimization: - Cached the Python executable path to avoid redundant searches. - Cached agent instructions to avoid redundant file reads. - Made the `read_text_file` function asynchronous to prevent blocking the event loop. * feat: Add comprehensive web app debugging with dap_launch This commit implements full web application debugging support using dap_launch and removes all non-functional dap_attach code, cleaning up the codebase. ## Key Changes ### Web App Debugging Implementation - Added Flask debugging example with launcher script (examples/web_flask/run_flask.py) - Created comprehensive automated tests (tests/test_web_app_debug.py) - Demonstrates HTTP-triggered breakpoints in web applications - Tests verify breakpoint hits in loops and variable inspection ### Code Cleanup - Removed dap_attach() function (187 lines) - does not work with debugpy - Removed DirectDAPClient references from mcp_server.py - Simplified StdioDAPClient to launch-only mode - Deleted non-functional attach mode logic ### Documentation Updates - agent_instructions.md: Added "Debugging Web Applications" section - docs/mcp_usage.md: Updated with web app debugging workflow - docs/DEBUGGING_WEB_APPS.md: New comprehensive guide - examples/web_flask/README.md: Complete rewrite with correct workflow - examples/gui_counter/README.md: Added GUI debugging instructions ### New Files - examples/web_flask/run_flask.py: Flask launcher for debugging - examples/gui_counter/run_counter_debug.py: GUI counter launcher - tests/test_web_app_debug.py: Automated web app debugging tests - docs/DEBUGGING_WEB_APPS.md: Comprehensive debugging guide ### Linting & Configuration - Fixed ruff, black, and mypy linting issues - Updated .pre-commit-config.yaml to exclude examples from mypy - Updated pyproject.toml with explicit package bases configuration - Added types-aiofiles for proper type checking ### Why dap_attach was removed The dap_attach approach was investigated but does not work with debugpy. When you run `python -m debugpy --listen`, debugpy does not work with debugpy does not respond to DAP attach requests. dap_launch is the unified solution for all debugging scenarios including web servers, GUI apps, and scripts. ### Test Results All 9 tests passing: - 7 core tests (mcp_server, cli, end-to-end) - 2 new web app debugging tests 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com> * feat: Add .envrc for automatic virtual environment activation * chore: Bump version to 0.2.0 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com> --------- Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com> Co-authored-by: Claude <noreply@anthropic.com>
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‎.envrc‎

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#!/bin/bash
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# Automatically activate the virtual environment when entering this directory
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# Requires direnv: https://direnv.net/
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# Check if .venv exists
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if [ -d ".venv" ]; then
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source .venv/bin/activate
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echo "✓ Activated virtual environment (.venv)"
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else
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echo "⚠ Virtual environment not found. Run: python -m venv .venv"
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fi

‎.pre-commit-config.yaml‎

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rev: v1.4.1
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hooks:
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- id: mypy
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args: ["--ignore-missing-imports"]
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args: ["--ignore-missing-imports", "--explicit-package-bases"]
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exclude: ^examples/
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additional_dependencies: [types-aiofiles>=25.0.0]

‎agent_instructions.md‎

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- `run_tests_json(pytest_args?: string[]) -> PytestJson`: runs pytest and returns the JSON report body.
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- `run_tests_focus(keyword: string) -> PytestJson`: focused run, equivalent to `pytest -k <keyword>`.
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- `dap_launch(program: string, cwd?: string, breakpoints?: number[], console?: string, wait_for_breakpoint?: boolean, breakpoint_timeout?: number)` -> orchestrated launch via `debugpy.adapter` (returns initialize/configuration/launch responses and optional stopped event).
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- `dap_launch(program: string, cwd?: string, breakpoints?: number[], breakpoints_by_source?: Dict[str, List[int]], stop_on_entry?: boolean, console?: string, wait_for_breakpoint?: boolean, breakpoint_timeout?: number)` -> orchestrated launch via `debugpy.adapter` (returns initialize/configuration/launch responses and optional stopped event). Use `breakpoints_by_source` to set breakpoints in imported modules or additional source files. **Use this for ALL debugging scenarios including web servers, long-running processes, and scripts.**
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- `dap_set_breakpoints(source_path: string, lines: number[])` -> resilient setBreakpoints (waits for late `initialized` when needed).
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- `dap_list_breakpoints()` -> returns the cached breakpoint map so you can confirm what has been registered.
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Note: The server retries breakpoint registration after the debug adapter sends `initialized`. This retry applies both to main-program breakpoints and entries provided via `breakpoints_by_source`. A further retry pass occurs after the first `stopped` event to catch imported-module timing races.
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- `dap_continue(thread_id?: number)` -> continues execution (auto-selects first thread if omitted).
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- `dap_step_over(thread_id?: number)` / `dap_step_in(thread_id?: number)` / `dap_step_out(thread_id?: number)` -> step controls that reuse the last stopped thread by default.
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- `dap_locals()` -> threads, stackTrace, scopes and variables for the current top frame.
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**Key workflow reminder:** Start new debugging sessions with a single `dap_launch` call that includes your breakpoint list. The launch helper performs `initialize`, registers breakpoints, issues `configurationDone`, and starts the target. You do **not** need to call `dap_set_breakpoints` beforehand unless you are adjusting breakpoints mid-session.
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### Example workflow (pseudo JSON-RPC calls)
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**Breakpoints in imported modules:** Use the `breakpoints_by_source` parameter to set breakpoints in any source file, not just the main program. This is essential for debugging multi-file applications and imported modules. Relative paths are resolved from `PROJECT_ROOT` first, then from `cwd` if provided. The tool implements a three-phase retry strategy to ensure breakpoints are registered even if modules aren't loaded yet when the adapter starts.
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## Debugging Web Applications (Flask, Django, FastAPI)
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**Use `dap_launch` for web applications!** The debugger controls the application lifecycle and allows you to set breakpoints that trigger on HTTP requests.
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### Steps
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1. **Launch the web app under debugger control:**
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```json
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{
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"name": "dap_launch",
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"input": {
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"program": "run_flask.py",
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"cwd": ".",
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"breakpoints_by_source": {
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"examples/web_flask/inventory.py": [18]
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},
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"wait_for_breakpoint": false
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}
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}
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```
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2. **Trigger breakpoints via HTTP requests:**
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```bash
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curl http://127.0.0.1:5001/total
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```
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3. **Wait for stopped event:**
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```json
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{ "name": "dap_wait_for_event", "input": { "name": "stopped", "timeout": 10 } }
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```
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4. **Inspect variables and debug:**
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```json
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{ "name": "dap_locals" }
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{ "name": "dap_step_over" }
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{ "name": "dap_continue" }
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```
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5. **Clean up:**
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```json
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{ "name": "dap_shutdown" }
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```
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**Important:** Create a launcher script (like `run_flask.py`) that imports your web app as a module to avoid relative import issues. Example:
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```python
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from examples.web_flask import app
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if __name__ == "__main__":
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app.main()
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```
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**Why not dap_attach?** The `dap_attach` approach was investigated but does not work with debugpy. When you run `python -m debugpy --listen`, debugpy does not respond to DAP attach requests. Use `dap_launch` for all debugging scenarios.
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## Example workflow for scripts
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1. Configure your MCP client (VS Code, Claude Desktop, etc.) so it references `.venv/bin/python src/mcp_server.py`.
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2. Launch the debugger session:
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7. At any point, run tests with `{ "name": "run_tests_json" }` or `{ "name": "run_tests_focus", "input": { "keyword": "..." } }`.
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---
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If you need a fresh demo script, call `{ "name": "ensure_demo_program", "input": { "directory": "/tmp/debug_demo" } }` (or omit `directory` to use the default location) before launching the debugger. The response includes `launchInput` you can pass straight to `dap_launch`. Use `{ "name": "read_text_file", "input": { "path": "/tmp/debug_demo/demo_program.py" } }` if you want to review the script first.
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*Note:* The stdio client prints incoming events as `[dap:event] ...` for debugging. Feel free to keep or remove these prints in `src/dap_stdio_client.py` depending on your logging needs.

‎docs/DEBUGGING_WEB_APPS.md‎

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# Debugging Web Applications with dap_launch
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This document explains the **correct and only** way to debug web applications (Flask, Django, FastAPI, etc.) using this MCP debugging server.
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## TL;DR
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**Use `dap_launch` for ALL debugging, including web apps.** The `dap_attach` approach does not work with debugpy.
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## How to Debug Web Apps
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### 1. Create a Launcher Script
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Create a script like `run_flask.py` that imports your web app as a module:
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```python
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from examples.web_flask import app
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if __name__ == "__main__":
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app.main()
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```
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This avoids relative import issues when the debugger launches your app.
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### 2. Launch with dap_launch
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Use the MCP `dap_launch` tool to start your web app under debugger control:
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```json
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{
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"name": "dap_launch",
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"input": {
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"program": "run_flask.py",
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"cwd": ".",
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"breakpoints_by_source": {
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"examples/web_flask/inventory.py": [18]
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},
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"wait_for_breakpoint": false
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}
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}
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```
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**Key points:**
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- Use `breakpoints_by_source` to set breakpoints in your business logic files
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- Set `wait_for_breakpoint=false` since you'll trigger breakpoints via HTTP requests
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- The debugger starts and controls the Flask/Django/FastAPI process
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### 3. Trigger Breakpoints via HTTP
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Make HTTP requests to your app to trigger breakpoints:
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```bash
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curl http://127.0.0.1:5001/total
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```
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### 4. Wait for Stopped Event
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```json
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{
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"name": "dap_wait_for_event",
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"input": {
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"name": "stopped",
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"timeout": 10
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}
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}
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```
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### 5. Inspect and Debug
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```json
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{"name": "dap_locals"}
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{"name": "dap_step_over"}
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{"name": "dap_continue"}
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```
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### 6. Clean Up
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```json
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{"name": "dap_shutdown"}
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```
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## Why Not dap_attach?
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The `dap_attach` approach was thoroughly investigated but **does not work with debugpy**.
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### What We Found
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When you run:
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```bash
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python -m debugpy --listen 5678 -m your.app
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```
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And then try to connect to it directly:
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1. ✅ `initialize` request works and gets a response
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2. ❌ `attach` request sent but **debugpy never responds**
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3. ❌ Connection times out
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### Why It Fails
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- **debugpy is not a full DAP server** when started with `--listen`
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- It's designed for IDE integration (VS Code), not pure DAP attach scenarios
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- The adapter (`debugpy.adapter`) doesn't support `--connect-to` flag
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- Direct TCP connection to debugpy doesn't follow standard DAP protocol for attach
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### What We Tried
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1. **DirectDAPClient**: Created a TCP client to connect directly to debugpy
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- Result: debugpy doesn't respond to attach requests
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2. **StdioDAPClient with --connect-to**: Modified to launch adapter with connection flag
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- Result: `debugpy.adapter` doesn't support `--connect-to` flag
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3. **Multiple debugpy command variations**: Tested different flags and modes
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- Result: All failed with the same issue - no response to attach requests
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### Conclusion
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**debugpy fundamentally does not support the DAP attach workflow for already-running processes.** This is not a bug in our implementation - it's how debugpy works.
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## The Solution: dap_launch for Everything
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`dap_launch` works perfectly for all scenarios:
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- ✅ **Regular scripts**: Debugger starts and stops with the script
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- ✅ **Web servers**: Debugger starts Flask/Django/FastAPI and keeps it alive
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- ✅ **Long-running processes**: Debugger controls the entire lifecycle
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- ✅ **Breakpoints on HTTP requests**: Set breakpoints, trigger via curl/browser
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- ✅ **Module imports**: Use `breakpoints_by_source` for any file
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## Example: Complete Flask Debugging Session
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```json
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// 1. Launch Flask under debugger
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{
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"name": "dap_launch",
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"input": {
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"program": "run_flask.py",
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"cwd": ".",
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"breakpoints_by_source": {
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"examples/web_flask/inventory.py": [18]
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},
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"wait_for_breakpoint": false
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}
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}
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// 2. Trigger breakpoint (in bash)
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// curl http://127.0.0.1:5001/total
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// 3. Wait for stopped event
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{
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"name": "dap_wait_for_event",
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"input": {
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"name": "stopped",
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"timeout": 10
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}
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}
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// 4. Inspect variables
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{
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"name": "dap_locals"
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}
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// 5. Continue execution
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{
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"name": "dap_continue"
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}
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// 6. Shutdown
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{
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"name": "dap_shutdown"
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}
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```
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## References
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- [agent_instructions.md](agent_instructions.md) - Complete MCP tool documentation
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- [docs/mcp_usage.md](docs/mcp_usage.md) - Detailed usage guide
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- [examples/web_flask/README.md](examples/web_flask/README.md) - Flask example walkthrough

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