Summary
- Preserve `text_elements` through custom prompt argument parsing and
expansion (named and numeric placeholders).
- Translate text element ranges through Shlex parsing using sentinel
substitution, and rehydrate text + element ranges per arg.
- Drop image attachments when their placeholder does not survive prompt
expansion, keeping attachments consistent with rendered elements.
- Mirror changes in TUI2 and expand tests for prompt parsing/expansion
edge cases.
Tests
- placeholders with spaces as single tokens (positional + key=value,
quoted + unquoted),
- prompt expansion with image placeholders,
- large paste + image arg combinations,
- unused image arg dropped after expansion.
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