LRC-LIB-CATALOG-IMPORT: an ARW6 is described from the whole file, not a partial read

header_plan skipped an ARW6's strip but its first 64 KB and then said Ready, while the ARW6
header probe (Mode::Header) validates every tile: its picture header, stream tables and the
first lines of its residual stream, which lie in the skipped bytes. The probe of the partly
read buffer then failed ("ARW6 first-half row count outside 2..=7") where the whole file
succeeds: sparse_corpus failed on arw6-sony-ilce7rm6-apsc-land-c.arw, the first ARW6 file it
reads (it stops at the first failure). Like NEF, ORF and PEF, whose header probes read
samples, an ARW6 now gets HeaderPlan::Whole from the header plan. The preview plan is
unchanged: the embedded preview reads no tile, and the 13 ARW previews in the corpus are
still read from 21 % of their bytes.

Only the test reads the header plan today (the app's partial reads use preview_plan), so no
import changes. New test: a synthetic two-tile ARW6 whose second tile lies past a first one
of bulk size (Ready before, Whole now). sparse_corpus passes on the 8 ILCE-7RM6 ARW6 files.

cargo test --workspace: 3205 passed, 1 failed, visualize::tests::
all_masks_overlay_shows_every_visible_mask_at_once, which fails on main b3d392b4 too
(PR #1456 addresses it); fmt, clippy, parity, layers, assets and wasm pass.

Sources: own design.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/raw/src/sparse.rs

@@ -13,9 +13,9 @@
 //! tracks (keeping the raw track's coding headers and quantization maps, and the timed-metadata
 //! track where Canon puts the as-shot white balance), a RAF's CFA strip (keeping its compression
 //! header) and a Panasonic RW2's raw data. Formats whose header probe reads samples (NEF: masked
-//! columns; ORF: bit depth and CFA phase; PEF: dark borders) and anything else get
-//! [`HeaderPlan::Whole`], as does a structure that is incomplete, inconsistent or keeps metadata
-//! inside its sample data: the plan never guesses.
+//! columns; ORF: bit depth and CFA phase; PEF: dark borders; ARW6, for its header plan only: the
+//! start of every tile) and anything else get [`HeaderPlan::Whole`], as does a structure that is
+//! incomplete, inconsistent or keeps metadata inside its sample data: the plan never guesses.
 
 use std::collections::HashSet;
 
@@ -236,6 +236,8 @@ fn tiff_plan(bytes: &[u8], loaded: &Ranges, preview: bool) -> HeaderPlan {
         let chunks: Vec<(u64, u64)> = match ifd.image() {
             // a preview's strips are read when the preview is wanted: only the raw image is skipped
             Ok(info) if preview && !matches!(info.photometric, t::photometric::CFA | t::photometric::LINEAR_RAW) => continue,
+            // (Sony Compressed RAW 2: the header probe decodes the start of every tile; a preview reads none)
+            Ok(info) if !preview && info.compression == 32766 => return HeaderPlan::Whole("an ARW6 header probe reads its tiles"),
             Ok(info) => info.chunks(len).iter().map(|c| (c.offset, c.len)).collect(),
             // a raw IFD without the tags a TIFF image needs (an older CR2's) still lists its strips
             Err(_) => match (ifd.u64s(t::STRIP_OFFSETS), ifd.u64s(t::STRIP_BYTE_COUNTS)) {
@@ -550,4 +552,17 @@ mod tests {
         raf[104..108].copy_from_slice(&1000u32.to_be_bytes());
         assert_eq!(run(&raf, 160, 0).0, HeaderPlan::Whole("RAF raw container"));
     }
+
+    /// An ARW6 header probe reads every tile's headers and the first lines of its data, which lie in the strip a
+    /// plan would skip: here the second tile, past a first one of bulk size.
+    #[test]
+    fn arw6_is_described_from_the_whole_file() {
+        use crate::vendor::arw6_testenc::{Qis, arw6_file, one_tile_quantised};
+        let (tile, _) = one_tile_quantised(64, 48, 0, Qis::REAL);
+        let mut first = tile.clone();
+        first.resize(BULK as usize, 0);
+        let file = arw6_file(&[(0, 0, 64, 48, first), (64, 0, 64, 48, tile)], 128, 48);
+        assert!(crate::probe_info(&file).is_ok());
+        assert_eq!(run(&file, 16, 0).0, HeaderPlan::Whole("an ARW6 header probe reads its tiles"));
+    }
 }