Print proxy URL when starting Dev Proxy in detach mode

[Copilot]

devproxy --port 0 --detach didn't show the assigned proxy port, making the proxy unusable since the caller can't know where to connect.

• ProxyEngine: After StartAsync(), update _config.Port from the actual endpoint port (resolves OS-assigned port for --port 0). Re-save state file when running as daemon so the parent process picks up the resolved value.
• Program.cs: Add Proxy URL line between PID and API URL in detach output. Wait for state.Port > 0 instead of just state existence to avoid reading stale port 0 before the engine updates it.

Dev Proxy started in background.

  PID:       6456
  Proxy URL: http://127.0.0.1:34251
  API URL:   http://127.0.0.1:8897
  Log file:  /Users/user/.config/dev-proxy/logs/devproxy-6456-2026-03-05.log

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• aka.ms
  • Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --as-system-proxy false --port 0 --api-port 0 --_internal-daemon (dns block)
  • Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy stop (dns block)
  • Triggering command: /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy /home/REDACTED/work/dev-proxy/dev-proxy/DevProxy/bin/Debug/net10.0/devproxy --as-system-proxy false --port 8000 --api-port 0 --_internal-daemon (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Print port number when starting Dev Proxy in detach mode</issue_title>
<issue_description>When you start Dev Proxy using devproxy --port 0 --output json --detach it shows the following output:

Dev Proxy started in background.

  PID:       6456
  API URL:   http://127.0.0.1:8897
  Log file:  C:\Users\scope\AppData\Local\dev-proxy\logs\devproxy-6456-2026-03-05-14-22-42.log

Use 'devproxy status' to check status.
Use 'devproxy logs' to view logs.
Use 'devproxy stop' to stop.

--port 0 means that a random port should be assigned to Dev Proxy. The output however doesn't show which port was assigned making it impossible to use Dev Proxy.

Between PID and API URL print the actual proxy URL and assigned port (even when explicitly specified through args)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Print port number when starting Dev Proxy in detach mode #1590

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[Copilot]

Pull request overview

Improves detached-mode startup output so callers can discover the actual proxy address when using OS-assigned ports (--port 0), by persisting the resolved proxy port and printing a Proxy URL in the parent process.

Changes:

• Update ProxyEngine to set the runtime port after the proxy endpoint is started, and (when running as the internal daemon) re-save the detached state file with the resolved port.
• Update detached-mode startup polling to wait for state.Port > 0 and print a new Proxy URL: line in the console output.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
DevProxy/Proxy/ProxyEngine.cs	After starting the proxy endpoint, updates the effective port and re-saves detached state with the resolved port for --port 0.
DevProxy/Program.cs	In detached startup output, waits for a non-zero port and prints the resolved Proxy URL alongside PID/API URL/log file.

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