Fixes an issue where PowerShell 7 installation suggestion text was not displayed when service-level hooks failed due to missing PowerShell, while the same suggestion worked correctly for command-level hooks and direct hook execution.

Problem

When PowerShell 7 is not installed and a service uses PowerShell hooks, the expected suggestion text was missing:

Expected behavior: All scenarios should show:

PowerShell 7 is not installed or not in the path. To install PowerShell 7, visit https://learn.microsoft.com/powershell/scripting/install/installing-powershell

Root Cause

The issue occurred in the EventDispatcher.RaiseEvent() method, which handles service lifecycle events. When a PowerShell hook failed:

1. PowerShell script returns ErrorWithSuggestion with installation guidance
2. Hook runner wraps the error (preserving the error chain)
3. EventDispatcher flattens ALL handler errors into a plain string using errors.New(strings.Join(...))
4. UX middleware can't detect ErrorWithSuggestion because it was converted to a generic error
5. Suggestion text is lost

Command hooks work correctly because they bypass the event dispatcher and go directly through the middleware chain.

Solution

Modified EventDispatcher.RaiseEvent() to preserve error types when there's only one handler error:

// Before: Always flattened errors
if len(handlerErrors) > 0 {
    lines := make([]string, len(handlerErrors))
    for i, err := range handlerErrors {
        lines[i] = err.Error()
    }
    return errors.New(strings.Join(lines, ","))
}

// After: Preserve single errors, join multiple errors
if len(handlerErrors) > 0 {
    // If there's only one error, return it directly to preserve error types like ErrorWithSuggestion
    if len(handlerErrors) == 1 {
        return handlerErrors[0]
    }
    
    // For multiple errors, join them as before
    lines := make([]string, len(handlerErrors))
    for i, err := range handlerErrors {
        lines[i] = err.Error()
    }
    return errors.New(strings.Join(lines, ","))
}

Testing

• Added comprehensive tests to verify ErrorWithSuggestion preservation through event dispatcher
• Verified existing multi-error aggregation behavior is unchanged
• Manually tested both scenarios now show suggestion text correctly
• All existing tests pass

Impact

This is a minimal, targeted fix that:

• ✅ Fixes service-level hook suggestion display
• ✅ Preserves all existing error handling behavior
• ✅ No breaking changes to any APIs
• ✅ Works for any ErrorWithSuggestion, not just PowerShell

Fixes #5453.

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