CmdPal: Use Shell API to determine the default browser in WebSearch

[jiripolasek]

Summary of the Pull Request

This PR introduces a new method for determining the default browser using the Windows Shell API. The new provider selects the browser associated with the HTTPS protocol (falling back to HTTP if necessary). The original implementation is retained as a fallback for now, and the codebase is prepared for future extensions (e.g., manual default-browser selection).

As a flyby, it also fixes an issue where commands continued showing the previous browser name if the user changed their default browser while the Command Palette was running.

One-liner for change log

Fixed default browser selection in the Web Search built-in extension.

PR Checklist

• Closes: Command Palette Web Search and Open URL do not respect default browser, use Microsoft Edge instead #42343
• Communication: I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected
• Tests: Added/updated and all pass
• Localization: All end-user-facing strings can be localized
• Dev docs: Added/updated
• New binaries: Added on the required places
  • JSON for signing for new binaries
  • WXS for installer for new binaries and localization folder
  • YML for CI pipeline for new test projects
  • YML for signed pipeline
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[github-actions]

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❌ Errors, Warnings, and Notices	Count
ℹ️ candidate-pattern	1
❌ forbidden-pattern	1
⚠️ ignored-expect-variant	4

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[Copilot]

Pull Request Overview

This PR refactors the default browser detection mechanism in the Command Palette's Web Search extension to use the Windows Shell API (AssocQueryStringW) as the primary method, with fallbacks to legacy registry access and Microsoft Edge. It introduces a service-based architecture with IBrowserInfoService and multiple provider implementations. The PR also fixes an issue where the browser name in the UI would not update when users changed their default browser while Command Palette was running.

Key Changes

• Introduced IBrowserInfoService interface and DefaultBrowserInfoService implementation with provider chain pattern
• Added ShellAssociationProvider using Windows Shell API for protocol associations (https/http)
• Retained legacy registry-based detection as LegacyRegistryAssociationProvider for fallback compatibility
• Updated all command items and pages to use the new browser info service for dynamic browser name retrieval

Reviewed Changes

Copilot reviewed 24 out of 25 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
Helpers/Browser/DefaultBrowserInfoService.cs	Core service orchestrating browser detection with caching and provider fallback chain
Helpers/Browser/Providers/ShellAssociationProvider.cs	Primary provider using AssocQueryStringW to query https/http protocol associations
Helpers/Browser/Providers/LegacyRegistryAssociationProvider.cs	Fallback provider using registry access for older browser detection method
Helpers/Browser/Providers/AssociationProviderBase.cs	Base class providing shared command parsing and indirect string resolution logic
Helpers/Browser/Providers/FallbackMsEdgeBrowserProvider.cs	Final fallback returning hardcoded Microsoft Edge path
Helpers/NativeMethods.cs	P/Invoke declarations for AssocQueryStringW shell API
Helpers/Browser/BrowserInfo.cs	Record type containing browser path, name, and arguments pattern
Helpers/Browser/IBrowserInfoService.cs	Service interface for retrieving default browser information
Helpers/Browser/BrowserInfoServiceExtensions.cs	Extension method for opening URLs in the default browser
Commands/SearchWebCommand.cs	Updated to use IBrowserInfoService instead of static DefaultBrowserInfo
Commands/OpenURLCommand.cs	Updated to use IBrowserInfoService for opening URLs
Pages/WebSearchListPage.cs	Updated to dynamically retrieve browser name via service
FallbackExecuteSearchItem.cs	Updated to get browser name dynamically on each query update
FallbackOpenURLItem.cs	Updated to get browser name dynamically and changed IsValidUrl to private
WebSearchTopLevelCommandItem.cs	Constructor now accepts IBrowserInfoService parameter
WebSearchCommandsProvider.cs	Creates shared DefaultBrowserInfoService instance and passes to all commands
Properties/Resources.resx	Added "default browser" localization resource as fallback display text
Tests/.../MockBrowserInfoService.cs	Mock implementation returning fixed browser info for unit tests
Tests/.../SettingsManagerTests.cs	Updated test to pass mock browser service
Tests/.../QueryTests.cs	Updated tests to pass mock browser service

Files not reviewed (1)

• src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WebSearch/Properties/Resources.Designer.cs: Language not supported

[Copilot]

Incomplete XML documentation: The <returns> element is empty and should describe what the method returns.

Should be:

/// <returns>A <see cref="BrowserInfo"/> object containing information about the default browser, or null if the browser information cannot be determined.</returns>

Suggested change

	/// <returns></returns>
	/// <returns>A <see cref="BrowserInfo"/> object containing information about the default browser, or null if the browser information cannot be determined.</returns>

[Copilot]

Missing XML documentation for public type: The BrowserInfo record is public but lacks XML documentation. All public types, properties, and members should be documented with XML comments explaining their purpose.

Add documentation like:

/// <summary>
/// Contains information about a web browser installation.
/// </summary>
public record BrowserInfo
{
    /// <summary>
    /// Gets the file path to the browser executable or a packaged application URI.
    /// </summary>
    public required string Path { get; init; }

    /// <summary>
    /// Gets the user-friendly name of the browser.
    /// </summary>
    public required string Name { get; init; }

    /// <summary>
    /// Gets the command line arguments pattern for launching URLs, or null if not applicable.
    /// </summary>
    public string? ArgumentsPattern { get; init; }
}

Suggested change

	public record BrowserInfo
	{
	public required string Path { get; init; }
	public required string Name { get; init; }
	/// <summary>
	/// Contains information about a web browser installation.
	/// </summary>
	public record BrowserInfo
	{
	/// <summary>
	/// Gets the file path to the browser executable or a packaged application URI.
	/// </summary>
	public required string Path { get; init; }
	/// <summary>
	/// Gets the user-friendly name of the browser.
	/// </summary>
	public required string Name { get; init; }
	/// <summary>
	/// Gets the command line arguments pattern for launching URLs, or null if not applicable.
	/// </summary>

[Copilot]

Potential null reference exception: On lines 23-24, progId could be null if both registry lookups fail (lines 17-22), but it's used in string interpolation without null checking. This will cause GetRegistryValue to be called with paths containing "null" as a string literal.

Add a null check:

var progId = GetRegistryValue(/*...*/)
             ?? GetRegistryValue(/*...*/);

if (string.IsNullOrEmpty(progId))
{
    return null;
}

var appName = GetRegistryValue($@"HKEY_CLASSES_ROOT\{progId}\Application", "ApplicationName")
              ?? GetRegistryValue($@"HKEY_CLASSES_ROOT\{progId}", "FriendlyTypeName");

Suggested change

	"ProgId");
	"ProgId");
	if (string.IsNullOrEmpty(progId))
	{
	return null;
	}

[Copilot]

Potential buffer overflow risk with stackalloc: On line 44, when cch > 512, a heap-allocated array is created, but when cch <= 512, stackalloc is used. However, the second call to AssocQueryStringW on line 48 might update cch to a larger value than initially reported, potentially overflowing the stack-allocated buffer.

The safer approach is to check cch hasn't changed after the second call:

var originalCch = cch;
var span = cch <= 512 ? stackalloc char[(int)cch] : new char[(int)cch];

fixed (char* p = span)
{
    var hr = NativeMethods.AssocQueryStringW(NativeMethods.AssocF.IsProtocol, what, protocol, null, p, ref cch);
    if (hr != 0 || cch == 0 || cch > originalCch)
    {
        return null;
    }
    // ...
}

Suggested change

	var span = cch <= 512 ? stackalloc char[(int)cch] : new char[(int)cch];
	fixed (char* p = span)
	{
	var hr = NativeMethods.AssocQueryStringW(NativeMethods.AssocF.IsProtocol, what, protocol, null, p, ref cch);
	if (hr != 0 || cch == 0)
	var originalCch = cch;
	var span = cch <= 512 ? stackalloc char[(int)cch] : new char[(int)cch];
	fixed (char* p = span)
	{
	var hr = NativeMethods.AssocQueryStringW(NativeMethods.AssocF.IsProtocol, what, protocol, null, p, ref cch);
	if (hr != 0 || cch == 0 || cch > originalCch)

[Copilot]

Default initialization removed for Arguments property: The Arguments property no longer has a default value of string.Empty. This could lead to a null reference exception if the property is accessed before being set, even though the constructor does set it.

Consider adding the default initializer back for defensive programming:

public string Arguments { get; internal set; } = string.Empty;

Suggested change

	public string Arguments { get; internal set; }
	public string Arguments { get; internal set; } = string.Empty;

[Copilot]

Race condition in UpdateIfTimePassed: There's a potential race condition where multiple threads could pass the timeout check (line 55) simultaneously before any of them updates _lastUpdateTickCount (line 60). This means multiple threads could enter the lock and call UpdateCore() unnecessarily.

Consider moving the timestamp update inside the lock:

public void UpdateIfTimePassed()
{
    var curTickCount = Environment.TickCount64;
    if (curTickCount - _lastUpdateTickCount < UpdateTimeout && _defaultBrowser != null)
    {
        return;
    }

    lock (_updateLock)
    {
        // Double-check after acquiring lock
        if (curTickCount - _lastUpdateTickCount < UpdateTimeout && _defaultBrowser != null)
        {
            return;
        }
        _lastUpdateTickCount = curTickCount;
        _defaultBrowser = UpdateCore();
    }
}
```suggestion
        lock (_updateLock)
        {
            // Double-check after acquiring lock
            if (curTickCount - _lastUpdateTickCount < UpdateTimeout && _defaultBrowser != null)
            {
                return;
            }
            _lastUpdateTickCount = curTickCount;