Copy Post: fix backslash characters being stripped when duplicating a post

[Gilmoursa]

Fixes #46020

Proposed changes

wp_update_post() calls wp_unslash() internally because it expects WordPress-style slashed data (as received from $_POST). The Copy Post module passed raw database content from get_post() directly — content that is already unslashed — so backslash sequences like \t, \n, \\, and \f were silently stripped from post_content, post_title, and post_excerpt when duplicating a post.

Fix: wrap the data array with wp_slash() before calling wp_update_post() in update_content(), which is the standard WordPress pattern for passing programmatically-constructed post data.

One-line change:

// Before
return wp_update_post( $data );

// After
return wp_update_post( wp_slash( $data ) );

Also adds a regression test using ReflectionMethod to invoke the protected update_content() method and assert that backslashes in all three fields are preserved after the copy.

Does this pull request change what data or activity we track or use?

No. This is a bug fix for data fidelity during post duplication. No tracking or privacy-relevant behaviour is changed.

Testing instructions

1. Enable the Copy Post module in Jetpack → Settings → Writing.
2. Create a post containing backslash characters, e.g. add a Code block with the text \t is a tab and a paragraph with \\escaped\\.
3. Save and publish the post.
4. Go to Posts → All Posts, find the post, and click Duplicate.
5. Open the duplicated post — the content should be identical to the original, with all backslashes intact.
   • Before this fix: \t is a tab becomes t is a tab; \\escaped\\ becomes \escaped\
   • After this fix: content is preserved exactly

🤖 Generated with Claude Code

[github-actions]

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