BUG - MDX Preview Breaks with Multi-word Placeholders

Requested by: @Aibono1225 via YakShaver.ai cc: @Marxoz, @jakebayliss, @Aibono1225, @amankumarrr, @adamcogan, @kulesy, @JackDevAU

Hi Team!

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Pain

Any placeholder in braces breaks a rich text field that uses the mdx parser. Word count is not the variable: a single-word placeholder fails just as hard as a multi-word one, and either way the whole field collapses to invalid markdown.

It is also destructive. Content authored with escaped braces parses fine, but Tina writes it back with the braces raw on save, so a file that worked stops parsing next time it is opened. That is what happened to the SSW rule in https://github.com/SSWConsulting/SSW.Rules.Content/pull/11601.

Approach

Re-encode braces when stringifying. Same root cause as https://github.com/tinacms/tinacms/issues/6324 (angle brackets), so fix them together.

Acceptance Criteria

1. A placeholder such as {{ REASON }} or {{ SOLUTION AND EXPLANATION }} renders in an mdx field without collapsing it, one word or many.
2. Escaped braces survive a save and reopen, so a document that parses today still parses after being edited in Tina.
3. Fields using the markdown parser keep working as they do now.

Screenshot

Figure: Adding a second word in markdown breaks the MDX preview rendering