Fix PowerShell command substitution argument parsing

[Copilot]

Fix PowerShell argument splitting for space-separated IDs

This PR addresses an issue where WP-CLI commands on Windows PowerShell incorrectly handle space-separated IDs from command substitution.

Problem

• On PowerShell, $(wp post list --post_type='page' --format=ids) returns IDs as a single string (e.g., "1164 1186")
• This causes commands like wp post delete $(...) to only process the first ID when the string is cast to int
• On Linux/Unix, the IDs are correctly separated into individual arguments

Solution

Added Windows-specific argument splitting logic in Runner::back_compat_conversions() to detect and split space-separated numeric IDs.

Implementation Details

The fix:

• Only activates on Windows (using Utils\is_windows())
• Only splits arguments that are entirely space-separated numeric IDs (regex: /^\d+(\s+\d+)+$/)
• Preserves non-numeric strings, single IDs, and strings with leading/trailing spaces as-is
• Uses array_push() with splat operator for better performance with large numbers of IDs
• Maintains backward compatibility with Unix-like behavior
• Includes comprehensive unit tests and Behat scenarios

Changes

• Implement Windows-specific argument splitting
• Add comprehensive unit tests
• Add Behat integration tests
• Pass all code quality checks
• Performance optimization using array_push with splat operator

Original prompt

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This section details on the original issue you should resolve

<issue_title>wp-cli subcommands on Windows Powershell</issue_title>
<issue_description>Looking at the official WP documentation here, the wp post delete command should be able to take a subcommand to list all the IDs to delete.

This works well on a Linux like system, but doesn't on Windows Powershell.

I know that it is more a Windows+Powershell issue, but that would be nice if we could find a workaround solution for this.

Expectations

# Delete all pages
$ wp post delete $(wp post list --post_type='page' --format=ids)
Success: Trashed post 1164.
Success: Trashed post 1186.

Reality

# Delete all pages
$ wp post delete $(wp post list --post_type='page' --format=ids)
Success: Trashed post 1164 1186.

In that case, post id 1186 has not been deleted because the subcommand result is interpreted as a single string parameter given to the delete command.
The \WP_CLI\CommandWithDBObject::_delete function that should receive $args as an array of IDs receive in reality one string param with the value 1164 1186 which evaluates as 1164 when casted to integer.

Function parameters type hint
Moreover, the wp_delete_post() function that is called underneath, should receive an integer value as first parameter.

/**
 * @param int  $postid       Optional. Post ID. Default 0.
 * @param bool $force_delete Optional. Whether to bypass Trash and force deletion.
 *                           Default false.
 * @return WP_Post|false|null Post data on success, false or null on failure.
 */
function wp_delete_post( $postid = 0, $force_delete = false ) {}

/**
 * Filters whether a post deletion should take place.
 *
 * @since 4.4.0
 *
 * @param WP_Post|false|null $delete       Whether to go forward with deletion. @TODO description
 * @param WP_Post            $post         Post object.
 * @param bool               $force_delete Whether to bypass the Trash.
 */
$check = apply_filters( 'pre_delete_post', null, $post, $force_delete );

I don't know if parameters hints will be enforced later, but there might be an issue there too as this function and the hooks triggered are all expecting an integer value.</issue_description>

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

@danielbachhuber Thanks for the report, @timotheemoulin !

I moved this issue to wp-cli/wp-cli because I think it's related to how arguments are passed/parsed on Powershell. Here's some past work on PowerShell compatibility, if it's helpful: https://github.com/ericmann/WP-PowerShell

Can you share wp cli info ?

Also, what happens when you run wp post delete 1164 1186? Do you see the same error as wp post delete $(wp post list --post_type='page' --format=ids) ?

As a point of reference, here's where WP-CLI reads $GLOBALS['argv']:

wp-cli/php/WP_CLI/Runner.php

Line 974 in b179c7a

$argv = array_slice( $GLOBALS['argv'], 1 );

• Fixes wp-cli subcommands on Windows Powershell #5679

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