`render --out p1.png` wrote a netpbm PAM stream (P7) whatever the name,
so a `.png` could not be opened by any PNG reader. The CLI already links
the engine, whose export module encodes PNG, JPEG and TIFF, so the output
format now follows the extension: `.png`, `.jpg`/`.jpeg` (quality 90),
`.tif`/`.tiff`, and `.pam` for the raw stream as before. Any other name
is refused up front, before the page is rendered, with the accepted list.
`export::encode_image` wraps the three encoders behind `ImageFormat` so
the CLI and `Exporter::image` share one match.
Tests (apps/pdfcraft-cli/tests/render.rs): a `.png` gets the PNG
signature and an IHDR with the rendered size; `.JPG` and `.tif` get
JPEG/TIFF magic; `.pam` still gets the P7 header and the right number of
bytes; `.bmp` fails with the message and writes nothing.
Co-authored-by: wstock <1394687+wstock@users.noreply.github.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>
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