S15.1: rawler reads back a linear DNG, so that is the container

A hand-rolled 64×48 LinearRaw DNG — one IFD, 16-bit RGB, DNGVersion,
ColorMatrix1, AsShotNeutral — comes back through rawler 0.7 with cpp 3,
the samples in the order written and the matrix parsed into the camera
definition; CameraProfile::extract builds a profile from it. ImageMagick
reads the same bytes.

dr_decode::decode currently accepts the file as CFA and passes three
times the samples on, so the cpp == 3 branch is the decode work FR-MRG-3
needs, and the only decode work. panorama.md §8 records the result.

docs/panorama.md

@@ -167,7 +167,7 @@ the way S9 calibrates R1.
 FR-MRG-3. Scene-linear, ≥ 16 bits, wide gamut, the first source's capture
 metadata, named from the first source with a `-pano` suffix, beside it.
 
-Two containers are candidates and S15.1 decides:
+Two containers were candidates and S15.1 decided, on 2026-09-19:
 
 - **Linear DNG.** `PhotometricInterpretation = LinearRaw`, three samples per
   pixel, `ColorMatrix1` carried from the first source. Re-enters through
@@ -178,9 +178,21 @@ Two containers are candidates and S15.1 decides:
   the existing encoder with a different sample type, and nothing about it is
   uncertain.
 
-Either way the composite enters the pipeline as a non-CFA, *linear* source —
-`from_rgba8`'s sibling with `non_linear = false` and the base curve resolved
-from the carried matrix — and is developed as any RAW is.
+**Linear DNG.** [`examples/linear_dng.rs`](../core/dr-decode/examples/linear_dng.rs)
+hand-rolls a 64 × 48 `LinearRaw` DNG — one IFD, uncompressed 16-bit RGB,
+`DNGVersion`, `ColorMatrix1`, `AsShotNeutral`, `CalibrationIlluminant1` — and
+rawler 0.7 reads it back: `cpp 3`, the samples interleaved as written, the
+matrix parsed into the camera definition, and `CameraProfile::extract` builds
+the same profile it would for a camera file. ImageMagick's libraw reads the
+same bytes. What does *not* yet work is `dr_decode::decode`, which accepts the
+file as CFA and hands the pipeline three times the samples it expects: the
+`cpp == 3` branch is the work, and it is the only decode work.
+
+The composite therefore enters the pipeline as a non-CFA, *linear* source —
+`from_rgba8`'s sibling with `non_linear = false` and the colour matrix carried
+from the DNG — and is developed as any RAW is. The writer is the example's
+IFD, grown up: tiled rather than one strip (FR-MRG-11 encodes per chunk), and
+carrying the first source's EXIF in a sub-IFD as `dr-export` already does.
 
 ## 9. Interaction
 

docs/traceability.md

@@ -9,18 +9,18 @@ Denominators are parsed from [`requirements.md`](requirements.md) at run time, n
 
 | Metric | Value |
 |---|---|
-| Source files scanned | 354 |
-| TRACES tags found | 1502 |
+| Source files scanned | 355 |
+| TRACES tags found | 1503 |
 | Requirements defined | 184 |
 | Requirements deferred (post-v1) | 24 |
-| Requirements covered | 142 |
-| **Coverage** | **77.2%** (142/184) |
+| Requirements covered | 143 |
+| **Coverage** | **77.7%** (143/184) |
 
 ### By type
 
 | Type | Covered | Defined |
 |---|---|---|
-| FR | 104 | 127 |
+| FR | 105 | 127 |
 | NFR | 34 | 50 |
 | R | 4 | 7 |
 
@@ -98,6 +98,7 @@ _None._
 | FR-EXP-7 | [`ui/dr-ui/src/activity.rs:83`](../ui/dr-ui/src/activity.rs#L83), [`ui/dr-ui/src/export.rs:1`](../ui/dr-ui/src/export.rs#L1), [`ui/dr-ui/src/export.rs:992`](../ui/dr-ui/src/export.rs#L992), [`ui/dr-ui/src/lib.rs:262`](../ui/dr-ui/src/lib.rs#L262), [`ui/dr-ui/src/lib.rs:2752`](../ui/dr-ui/src/lib.rs#L2752), [`ui/dr-ui/src/lib.rs:601`](../ui/dr-ui/src/lib.rs#L601), [`ui/dr-ui/src/lib.rs:647`](../ui/dr-ui/src/lib.rs#L647), [`ui/dr-ui/src/lib.rs:674`](../ui/dr-ui/src/lib.rs#L674), [`ui/dr-ui/src/library_ui.rs:4275`](../ui/dr-ui/src/library_ui.rs#L4275), [`ui/dr-ui/src/library_ui.rs:719`](../ui/dr-ui/src/library_ui.rs#L719), [`ui/dr-ui/src/library_ui.rs:8026`](../ui/dr-ui/src/library_ui.rs#L8026), [`ui/dr-ui/src/library_ui.rs:8103`](../ui/dr-ui/src/library_ui.rs#L8103), [`ui/dr-ui/src/library_ui.rs:8115`](../ui/dr-ui/src/library_ui.rs#L8115), [`ui/dr-ui/src/library_ui.rs:819`](../ui/dr-ui/src/library_ui.rs#L819), [`ui/dr-ui/src/library_ui.rs:876`](../ui/dr-ui/src/library_ui.rs#L876), [`ui/dr-ui/ui/app.slint:1091`](../ui/dr-ui/ui/app.slint#L1091), [`ui/dr-ui/ui/app.slint:1630`](../ui/dr-ui/ui/app.slint#L1630), [`ui/dr-ui/ui/library.slint:1583`](../ui/dr-ui/ui/library.slint#L1583), [`ui/dr-ui/ui/library.slint:4278`](../ui/dr-ui/ui/library.slint#L4278) |
 | FR-EXP-8 | [`core/dr-decode/src/lib.rs:330`](../core/dr-decode/src/lib.rs#L330), [`core/dr-decode/src/lib.rs:354`](../core/dr-decode/src/lib.rs#L354), [`core/dr-decode/src/lib.rs:368`](../core/dr-decode/src/lib.rs#L368), [`core/dr-decode/src/lib.rs:71`](../core/dr-decode/src/lib.rs#L71), [`core/dr-decode/src/lib.rs:79`](../core/dr-decode/src/lib.rs#L79), [`core/dr-decode/src/lib.rs:82`](../core/dr-decode/src/lib.rs#L82), [`core/dr-decode/src/locate.rs:1164`](../core/dr-decode/src/locate.rs#L1164), [`core/dr-decode/src/locate.rs:1223`](../core/dr-decode/src/locate.rs#L1223), [`core/dr-decode/src/locate.rs:316`](../core/dr-decode/src/locate.rs#L316), [`core/dr-decode/src/locate.rs:487`](../core/dr-decode/src/locate.rs#L487), [`core/dr-decode/src/locate.rs:571`](../core/dr-decode/src/locate.rs#L571), [`core/dr-decode/src/locate.rs:584`](../core/dr-decode/src/locate.rs#L584), [`core/dr-decode/src/locate.rs:667`](../core/dr-decode/src/locate.rs#L667), [`core/dr-export/examples/export.rs:99`](../core/dr-export/examples/export.rs#L99), [`core/dr-export/src/encode.rs:117`](../core/dr-export/src/encode.rs#L117), [`core/dr-export/src/encode.rs:161`](../core/dr-export/src/encode.rs#L161), [`core/dr-export/src/encode.rs:1`](../core/dr-export/src/encode.rs#L1), [`core/dr-export/src/encode.rs:206`](../core/dr-export/src/encode.rs#L206), [`core/dr-export/src/encode.rs:235`](../core/dr-export/src/encode.rs#L235), [`core/dr-export/src/encode.rs:311`](../core/dr-export/src/encode.rs#L311), [`core/dr-export/src/encode.rs:325`](../core/dr-export/src/encode.rs#L325), [`core/dr-export/src/encode.rs:408`](../core/dr-export/src/encode.rs#L408), [`core/dr-export/src/encode.rs:456`](../core/dr-export/src/encode.rs#L456), [`core/dr-export/src/encode.rs:70`](../core/dr-export/src/encode.rs#L70), [`core/dr-export/src/encode.rs:795`](../core/dr-export/src/encode.rs#L795), [`core/dr-export/src/encode.rs:809`](../core/dr-export/src/encode.rs#L809), [`core/dr-export/src/encode.rs:850`](../core/dr-export/src/encode.rs#L850), [`core/dr-export/src/encode.rs:898`](../core/dr-export/src/encode.rs#L898), [`core/dr-export/src/exif.rs:1`](../core/dr-export/src/exif.rs#L1), [`core/dr-export/src/lib.rs:136`](../core/dr-export/src/lib.rs#L136), [`core/dr-export/src/metadata.rs:1`](../core/dr-export/src/metadata.rs#L1), [`core/dr-export/src/metadata.rs:41`](../core/dr-export/src/metadata.rs#L41), [`core/dr-export/src/metadata.rs:74`](../core/dr-export/src/metadata.rs#L74), [`core/dr-types/src/lib.rs:655`](../core/dr-types/src/lib.rs#L655), [`core/dr-types/src/settings.rs:647`](../core/dr-types/src/settings.rs#L647), [`ui/dr-ui/src/develop.rs:4539`](../ui/dr-ui/src/develop.rs#L4539), [`ui/dr-ui/src/develop.rs:4651`](../ui/dr-ui/src/develop.rs#L4651), [`ui/dr-ui/src/develop.rs:729`](../ui/dr-ui/src/develop.rs#L729), [`ui/dr-ui/src/export.rs:467`](../ui/dr-ui/src/export.rs#L467), [`ui/dr-ui/src/export.rs:634`](../ui/dr-ui/src/export.rs#L634), [`ui/dr-ui/src/export.rs:680`](../ui/dr-ui/src/export.rs#L680), [`ui/dr-ui/src/export.rs:702`](../ui/dr-ui/src/export.rs#L702), [`ui/dr-ui/src/export.rs:826`](../ui/dr-ui/src/export.rs#L826), [`ui/dr-ui/src/export.rs:844`](../ui/dr-ui/src/export.rs#L844), [`ui/dr-ui/src/lib.rs:262`](../ui/dr-ui/src/lib.rs#L262), [`ui/dr-ui/src/lib.rs:285`](../ui/dr-ui/src/lib.rs#L285), [`ui/dr-ui/src/lib.rs:633`](../ui/dr-ui/src/lib.rs#L633), [`ui/dr-ui/src/settings_ui.rs:1`](../ui/dr-ui/src/settings_ui.rs#L1) |
 | FR-EXP-9 | [`core/dr-decode/src/lib.rs:510`](../core/dr-decode/src/lib.rs#L510), [`core/dr-export/src/lib.rs:128`](../core/dr-export/src/lib.rs#L128), [`core/dr-export/src/lib.rs:1`](../core/dr-export/src/lib.rs#L1), [`core/dr-gpu/src/adjust.rs:1106`](../core/dr-gpu/src/adjust.rs#L1106), [`ui/dr-ui/examples/face_native.rs:1`](../ui/dr-ui/examples/face_native.rs#L1), [`ui/dr-ui/src/develop.rs:4672`](../ui/dr-ui/src/develop.rs#L4672), [`ui/dr-ui/src/develop.rs:4710`](../ui/dr-ui/src/develop.rs#L4710), [`ui/dr-ui/src/develop.rs:6878`](../ui/dr-ui/src/develop.rs#L6878), [`ui/dr-ui/src/lib.rs:601`](../ui/dr-ui/src/lib.rs#L601), [`ui/dr-ui/src/library.rs:4052`](../ui/dr-ui/src/library.rs#L4052), [`ui/dr-ui/src/library.rs:4522`](../ui/dr-ui/src/library.rs#L4522), [`ui/dr-ui/src/library.rs:4558`](../ui/dr-ui/src/library.rs#L4558), [`ui/dr-ui/tests/export_ignores_the_viewport.rs:1`](../ui/dr-ui/tests/export_ignores_the_viewport.rs#L1) |
+| FR-MRG-3 | [`core/dr-decode/examples/linear_dng.rs:1`](../core/dr-decode/examples/linear_dng.rs#L1) |
 | FR-NC-1 | [`core/dr-sync-nextcloud/src/auth.rs:132`](../core/dr-sync-nextcloud/src/auth.rs#L132), [`core/dr-sync-nextcloud/src/auth.rs:44`](../core/dr-sync-nextcloud/src/auth.rs#L44), [`core/dr-sync-nextcloud/src/provider.rs:1`](../core/dr-sync-nextcloud/src/provider.rs#L1), [`core/dr-sync/src/account.rs:361`](../core/dr-sync/src/account.rs#L361), [`ui/dr-ui/src/launch.rs:277`](../ui/dr-ui/src/launch.rs#L277), [`ui/dr-ui/src/launch.rs:61`](../ui/dr-ui/src/launch.rs#L61), [`ui/dr-ui/src/launch_ui.rs:417`](../ui/dr-ui/src/launch_ui.rs#L417) |
 | FR-NC-10 | [`core/dr-sync/src/account.rs:226`](../core/dr-sync/src/account.rs#L226), [`ui/dr-ui/src/export.rs:1`](../ui/dr-ui/src/export.rs#L1), [`ui/dr-ui/src/lib.rs:674`](../ui/dr-ui/src/lib.rs#L674), [`ui/dr-ui/src/library.rs:1170`](../ui/dr-ui/src/library.rs#L1170), [`ui/dr-ui/src/library.rs:2463`](../ui/dr-ui/src/library.rs#L2463), [`ui/dr-ui/src/library.rs:589`](../ui/dr-ui/src/library.rs#L589), [`ui/dr-ui/src/library.rs:916`](../ui/dr-ui/src/library.rs#L916), [`ui/dr-ui/src/library_ui.rs:2062`](../ui/dr-ui/src/library_ui.rs#L2062), [`ui/dr-ui/src/library_ui.rs:4275`](../ui/dr-ui/src/library_ui.rs#L4275), [`ui/dr-ui/src/library_ui.rs:660`](../ui/dr-ui/src/library_ui.rs#L660), [`ui/dr-ui/src/sidecar_cache.rs:1`](../ui/dr-ui/src/sidecar_cache.rs#L1) |
 | FR-NC-12 | [`core/dr-sync-folder/src/lib.rs:1`](../core/dr-sync-folder/src/lib.rs#L1), [`core/dr-sync-nextcloud/src/lib.rs:1022`](../core/dr-sync-nextcloud/src/lib.rs#L1022), [`core/dr-sync-nextcloud/src/lib.rs:40`](../core/dr-sync-nextcloud/src/lib.rs#L40), [`core/dr-sync-nextcloud/src/provider.rs:1`](../core/dr-sync-nextcloud/src/provider.rs#L1), [`core/dr-sync/src/account.rs:1`](../core/dr-sync/src/account.rs#L1), [`core/dr-sync/src/account.rs:87`](../core/dr-sync/src/account.rs#L87), [`core/dr-sync/src/lib.rs:218`](../core/dr-sync/src/lib.rs#L218), [`core/dr-sync/src/lib.rs:51`](../core/dr-sync/src/lib.rs#L51), [`core/dr-sync/src/provider.rs:106`](../core/dr-sync/src/provider.rs#L106), [`core/dr-sync/src/provider.rs:1`](../core/dr-sync/src/provider.rs#L1), [`core/dr-sync/src/provider.rs:53`](../core/dr-sync/src/provider.rs#L53), [`core/dr-sync/src/reachability.rs:1`](../core/dr-sync/src/reachability.rs#L1), [`ui/dr-ui/src/remote.rs:1`](../ui/dr-ui/src/remote.rs#L1) |
@@ -208,7 +209,7 @@ Defined in `requirements.md` and marked `(post-v1)` on the defining line. Not in
 
 ## Not yet tagged
 
-42 of 184 requirements have no implementation tag. Expected while the codebase is young; each should gain one as it is built.
+41 of 184 requirements have no implementation tag. Expected while the codebase is young; each should gain one as it is built.
 
 <details><summary>Show untagged requirements</summary>
 
@@ -224,7 +225,6 @@ Defined in `requirements.md` and marked `(post-v1)` on the defining line. Not in
 - FR-MRG-10
 - FR-MRG-11
 - FR-MRG-2
-- FR-MRG-3
 - FR-MRG-4
 - FR-MRG-5
 - FR-MRG-6