Record where a linear DNG too large for one texture goes

ARCH §5.3 still described only a tile cache nobody built; it now says
what 0.19.0 tiles and what it does not: a linear DNG past PROXY_EDGE
opens on a reduced copy, a finer render samples a full-resolution
window, and the export is cut into halo-grown tiles. display-and-
extension.md's FR-DSP-2 row said absent, outstanding.md said the halo
had nothing to read it and that such a file fell to the embedded
preview.

rawler now builds from third_party, which ARCH's stack table and §3.2,
the root Cargo.toml's comment ("two upstream crates ... for Android")
and third_party/README.md's bump procedure did not know; the README
also names each vendored crate's licence. panorama.md and the manual
say a composite this wide develops and exports.

docs/dev/panorama.md

@@ -606,3 +606,13 @@ the preview (`grey_if_blown` in `dr_ui::merge`) now write a blown sample,
 before the gain, as the camera value the composite's balance maps to grey —
 the develop pipeline's neutral, fading in from `CLIP_ONSET` exactly as the
 develop's does.
+
+**A composite this wide is past two limits, both lifted the same day.**
+They were found on a 22 927 × 8966 panorama from Lightroom, and the fixture's
+own composite (22 993 × 5 980, §11) is past both. rawler's allocation guard,
+sized in samples but worded in pixels, refuses a three-sample DNG past about
+16 700 pixels wide; the copy in `third_party/` carries it raised
+([README](../../third_party/README.md)). And no texture holds such a frame:
+a linear DNG past 8192 pixels now opens on a box-reduced copy, a render finer
+than the copy samples a window of the full resolution, and the export is drawn
+in tiles (FR-DSP-2's note in requirements.md, ARCH §5.3).