How the Agent Reach Doctor Command Detects and Reports Active Backend Status

The doctor command executes per-channel health probes via the check() method, captures the active_backend attribute from each channel instance, and renders a Rich-formatted report showing which backend is currently active for each supported platform.

Agent Reach is an open-source automation framework that abstracts multiple platform APIs behind a unified channel interface. The doctor command serves as the built-in health checker, verifying that upstream tools are installed, configured, and executable. Understanding how it detects and reports the active backend status is essential for debugging connectivity issues and validating your local environment.

How the Doctor Command Orchestrates Backend Detection

Channel discovery starts in agent_reach/channels/__init__.py, which maintains an ALL_CHANNELS list containing instantiated channel classes. The get_all_channels() function returns this registry, providing the doctor with a complete inventory of platforms to validate.

When agent_reach/doctor.py runs, it iterates over this registry and invokes the health-check protocol defined in the abstract base class.

Channel Registry and Discovery

The agent_reach/channels/__init__.py file automatically registers every available channel implementation. It exposes get_all_channels(), which the doctor command calls to obtain the list of channel objects that require health validation.

Per-Channel Health Probing

Each concrete channel inherits from agent_reach/channels/base.py. The abstract Channel class defines an active_backend attribute and a check() method that subclasses must override.

During the probe, a channel executes a lightweight command—typically via agent_reach.probe.probe_command—to verify that a candidate backend binary exists and responds correctly. When successful, the channel assigns the working backend name to self.active_backend.

Aggregating the Active Backend Status

Inside agent_reach/doctor.py, the orchestration logic captures the results:

status, message = ch.check(config)            # channel does its own probing

active = getattr(ch, "active_backend", None) # whatever the channel set

The resulting dictionary stores status, message, and active_backend for each channel. The format_report() function then constructs a human-readable summary using Rich styling.

Reading the Active Backend from Source Code

The detection mechanism relies on the check() method setting the active_backend instance variable. In doctor.py, the code explicitly retrieves this attribute using getattr with a fallback to None when no backend is detected.

The format_report() function uses the _name_msg helper to append the active backend information to the status line. When a channel supports multiple backends and one is active, the report displays "（当前后端： ）" next to the channel name.

Running the Doctor Command

Execute the health check from your terminal to see active backend detection in action:

python -m agent_reach.cli doctor

Typical output shows the backend name in dim text:

[bold cyan]Agent Reach 状态[/bold cyan]
...
✅ 装好即用：
  ✅  YouTube — YouTube 视频和字幕 [dim]（当前后端：yt-dlp）[/dim]
...
状态：[green]9/12[/green] 个渠道可用

In this example, the YouTube channel reports yt-dlp as the active backend because its check() method successfully probed that executable.

Programmatically Accessing Backend Status

You can invoke the health check programmatically without using the CLI:

from agent_reach.doctor import check_all
from agent_reach.config import Config

cfg = Config()
health = check_all(cfg)

# Access the active backend for a specific channel

print(health["youtube"]["active_backend"])   # Output: "yt-dlp"

This returns a dictionary mapping channel names to their health status, including the detected active_backend.

Summary

• Channel Registry: agent_reach/channels/__init__.py provides get_all_channels() to enumerate all platforms.
• Health Probing: Each channel's check() method in agent_reach/channels/base.py sets active_backend after verifying the backend executable.
• Orchestration: agent_reach/doctor.py loops through channels, captures the active_backend attribute, and aggregates results.
• Reporting: The format_report() function renders active backend information using Rich text formatting.

Frequently Asked Questions

What happens if no backend is detected for a channel?

If the check() method fails to find a working backend, the active_backend attribute remains unset. The doctor report displays the channel status as unavailable or degraded, and the formatted output omits the backend name annotation.

How does a channel determine which backend is active?

Concrete channel implementations in agent_reach/channels/<platform>.py override the check() method to test candidate backends sequentially. They typically call agent_reach.probe.probe_command to verify binary existence and basic functionality, then assign the first successful candidate to self.active_backend.

Can I use the doctor command in CI/CD pipelines?

Yes. Run python -m agent_reach.cli doctor as a validation step. The command returns a non-zero exit code if critical channels are unhealthy, and the JSON-compatible output from check_all() can be parsed to verify specific backend availability before deployment.

Where is the active backend information stored after detection?

The active_backend string is stored as an instance attribute on the channel object during the check() execution. agent_reach/doctor.py extracts this value via getattr(ch, "active_backend", None) and persists it in the results dictionary passed to the formatting functions.

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    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
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}