[TartanLeGrand]

Draft, stacked on #2 (its first commit is #2's commit). Opened mostly to share what was learned about App Store Connect and Assets.car; it does not fix the problem it was written for, see below.

The problem

A production Tauri app built on Linux (xtool, AssetKit for the asset catalog) uploads to App Store Connect without error: the build upload reaches COMPLETE and the signature is accepted. The build is then never created: it stays in PROCESSING with no error, no warning and no e-mail. Bisected with IPAs that differ in one thing only (same harness, same signing, same upload path):

IPA	Result
Xcode 26.5 export, re-signed	VALID in about 2 min
Xcode export, DT keys and SDK changed to the Linux build's	VALID in about 2 min
Xcode export with the Linux-built executables	VALID in about 2 min
Linux build	stuck (more than 40 min)
Linux build, launch storyboard from Xcode	stuck
Linux build, actool Assets.car, PNGs and icon keys	VALID in about 7 min
Linux build, only Assets.car replaced by actool's	VALID in about 2 min

So the Assets.car is the cause. Both catalogs hold the same set of icon renditions, 1024 store icon included. A plausible explanation is that App Store processing extracts the store icon from the catalog and silently stalls on a catalog it cannot read, instead of rejecting it.

What this PR does

Brings the output closer to actool 26.5, one switchable group at a time (OutputOptions):

• dimension1Key: ten-attribute KEYFORMAT with Dimension1, a slot in every rendition key, and the matching BITMAPKEYS descriptor size.
• multisizeIcons: the part=218 icon size index records, the iPhone 60pt@3x copy at subtype 1792, and the BITMAPKEYS idiom / icon index masks.
• actoolIdentifiers: the NameIdentifier actool gives to AppIcon (6849; the hash behind it is unknown, other names keep CRC32 & 0xFFFF).
• actoolVersionStrings: CoreUI 975 and Xcode 26.5 strings in CARHEADER and EXTENDED_METADATA. Opt-in only, since it claims a tool that did not write the file; it was only there to test whether Apple's processing looks at it. I would drop it before merging.

The default becomes actoolStructure (the first three); .legacy reproduces the previous output. Tests add a small CAR reader and check the shape against what was dumped from an Xcode-built catalog. CARHEADER, KEYFORMAT and EXTENDED_METADATA (apart from the tool strings) and the 23 AppIcon rendition keys now match the Xcode file.

Result against App Store Connect

Each candidate replaced only Assets.car in the otherwise identical Linux IPA:

Candidate	Result
previous output (.legacy)	stuck (more than 16 min)
dimension1Key	stuck (more than 19 min)
+ actoolVersionStrings + multisizeIcons	stuck (more than 26 min)
+ actoolIdentifiers (same rendition keys as actool)	stuck (more than 16 min)

None of them is enough. What still differs from actool: actool stores the small icons in ZZZZPackedAsset atlas renditions (element 9, part 181) and writes layout 0x3eb link records pointing into them, where AssetKit writes plain bitmaps; the LZFSE output differs; and so does the BOM block numbering. The next step I would try is the other direction: start from actool's Assets.car (which passes) and swap one family of renditions at a time for AssetKit's (the store icon alone, then the packed small icons, then the compression), which needs a .car rewriting tool. Until then, a workaround is to ship an Assets.car compiled once by actool.

How was it tested?

• swift test on Linux x86_64 (Podman, Swift 6.4): Test run with 48 tests in 14 suites passed.
• Real uploads as above.

Developed with AI assistance; validated against App Store Connect as described above.

[coderabbitai]

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