Metadata

[Polkas]

Add metadata argument to export_to() with JSON sidecar support

Introduces an opt-in metadata argument to export_to() that records set_cell() text values alongside exported files.

What's new

• export_to() gains a metadata argument ("none" / "sidecar"). Passing "sidecar" writes a <file>.json sidecar next to the output — a flat JSON object for single-page exports, or a JSON array (one entry per page) for multi-page PDFs.
• A gridify.export.metadata global option allows project-wide defaults (e.g. in .Rprofile).
• Internal helpers extracted to gridify-utils.R: gridify_metadata(), gridify_to_json(), write_metadata_sidecar(), resolve_export_metadata().
• jsonlite added as Suggests (not Imports) — only required when metadata = "sidecar" is used; a clear requireNamespace guard provides an install prompt otherwise.

Tests & docs

• New test files: test_export_to.R, test_gridify_to_json.R.
• New man pages for all internal helpers.
• Vignettes (simple_examples, multi_page_examples) and NEWS.md updated.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.38710% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.47%. Comparing base (45855f1) to head (c90575a).

Files with missing lines	Patch %	Lines
R/gridify-utils.R	97.43%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
- Coverage   99.56%   99.47%   -0.09%     
==========================================
  Files           9        9              
  Lines         919      955      +36     
==========================================
+ Hits          915      950      +35     
- Misses          4        5       +1     

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[Polkas]

#15