Allow multiple Dev Proxy instances when asSystemProxy is false

[Copilot]

The detached mode single-instance check unconditionally blocks new instances regardless of asSystemProxy. When asSystemProxy is false, instances don't conflict over system proxy registration and should be allowed to coexist.

Changes

• ProxyInstanceState — Track asSystemProxy in the state file (defaults to true for backward compat with existing state files)
• DevProxyConfigOptions — Register --as-system-proxy for early CLI arg parsing before full config load
• StateManager — Switch from a single shared state.json to per-instance state files (state-{pid}.json) to avoid cross-instance interference. Each instance writes/deletes only its own file. LoadStateAsync() prefers the system-proxy instance, then falls back to the most recently started one. FindSystemProxyInstanceAsync() scans all state files to reliably detect a running system-proxy instance. Legacy state.json is still read for backward compatibility.
• Program.cs — Use FindSystemProxyInstanceAsync() for the system-proxy conflict check; use LoadStateByPidAsync(process.Id) in the detached startup wait loop to find the specific child process; resolve asSystemProxy from CLI args → config file fallback and persist to state
• StopCommand — Pass the specific state.Pid to DeleteStateAsync to avoid accidentally removing another instance's state file

// Before: single state.json, blocks unconditionally
if (await StateManager.IsInstanceRunningAsync()) { ... }

// After: per-instance state-{pid}.json, blocks only when a system-proxy instance exists
var systemProxyInstance = await StateManager.FindSystemProxyInstanceAsync();
if (systemProxyInstance is not null) { ... }

Original prompt

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This section details on the original issue you should resolve

<issue_title>When asSystemProxy is false allow running multiple instances</issue_title>
<issue_description>When asSystemProxy is false allow running multiple instances of Dev Proxy. Right now, you get the following error:

Dev Proxy is already running (PID: 1234).
Use 'devproxy stop' to stop it first.

This error stands but only if Dev Proxy was started with asSystemProxy: true. If it's false, then it should be possible to start multiple instances of Dev Proxy.</issue_description>

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

• Fixes When asSystemProxy is false allow running multiple instances #1586

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[Copilot]

Pull request overview

Updates detached-mode instance detection so Dev Proxy only blocks starting a new detached instance when an existing detached instance owns the system proxy, enabling coexistence when asSystemProxy is false.

Changes:

• Add asSystemProxy to the detached instance state file (defaulting to true for backward compatibility).
• Parse --as-system-proxy early via DevProxyConfigOptions so it can be persisted into detached state.
• Change detached startup logic to gate the “already running” check on existingState.AsSystemProxy.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
DevProxy/State/ProxyInstanceState.cs	Adds AsSystemProxy to persisted detached state (back-compat default true).
DevProxy/Program.cs	Gates detached single-instance check on existingState.AsSystemProxy and persists asSystemProxy into state.
DevProxy/Commands/DevProxyConfigOptions.cs	Adds early parsing access for --as-system-proxy before full config load.

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[waldekmastykarz]

@copilot apply changes based on the comments in this thread

[Copilot]

@copilot apply changes based on the comments in this thread

Applied the review feedback in 0170b3d. StateManager now uses per-instance state files (state-{pid}.json) instead of a single shared state.json:

• Each instance writes/deletes only its own state-{pid}.json — no cross-instance interference
• LoadStateAsync() scans all state files and prefers the system-proxy instance
• FindSystemProxyInstanceAsync() is used for the startup conflict check
• LoadStateByPidAsync(pid) is used in the detached startup wait loop to find the specific child process
• StopCommand passes state.Pid to DeleteStateAsync so it only removes the targeted instance's file
• Legacy state.json is still read for backward compatibility with pre-upgrade instances