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midi-harbor/specs/016-app-store-submission/research.md
James Coleman 9eede3b366 fix(appstore): drop winit's private blur call that App Review refused 
- App Review's automated check rejected the first submission for importing the private `CGSSetWindowBackgroundBlurRadius`. winit's macOS backend calls it for window blur, and the import stays in the binary although no window here asks for blur.
- Every winit crate is now patched to grmrgecko/winit, which is libcosmic's pinned revision with the private calls removed and blur doing nothing on macOS. The fork has to move whenever the libcosmic revision does.
- The App Store bundle is no longer signed when either executable imports a private window server symbol, so a dependency update cannot bring one back unnoticed.
- The `com.apple.security.network.server` entitlement, which the same check questioned, stays: network ports bind UDP and take incoming sessions. R-110 records the answer given to App Review.
2026-10-03 09:39:12 -05:00

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Research: App Store Submission

The investigation behind this spec, under its number in the project-wide research log.

R-103: What App Store Connect needs beyond the sandboxed app

Status: VERIFIED (2026-09-28) locally; not yet uploaded. Built as T245.

The App ID needs no capabilities. Every entitlement the build uses (the sandbox, network client and server, Bluetooth, USB, and the helper's inherit) is a sandbox entitlement that signing grants. The login item uses SMAppService, and the helper shares the app's container by inheriting its sandbox, so App Groups are not needed either. The profile Apple generated for the bare App ID carries com.apple.application-identifier, com.apple.developer.team-identifier and keychain-access-groups (<team>.*). The first two must be in the app's signed entitlements to match the profile; keychain access groups are not used, so they are left out.

The certificates came untrusted. Xcode created the Apple Distribution and Mac Installer Distribution certificates, but security find-identity called both CSSMERR_TP_NOT_TRUSTED: they are issued by Apple's WWDR G3 intermediate, which this Mac lacked. The Developer ID certificate, issued by another intermediate, was unaffected. Installing AppleWWDRCAG3.cer made both valid. The keychain names the installer certificate "3rd Party Mac Developer Installer", its older name, which is what the build looks for.

The helper keeps only the sandbox and inherit. A helper signed to inherit its parent's sandbox must carry exactly those two entitlements, so the profile's identifiers go on the app alone.

The build number is the build's time. App Store Connect refuses a build number it has seen for the app, so CFBundleVersion is the time in UTC, %Y%m%d%H%M, twelve digits. The version shown, CFBundleShortVersionString, stays VERSION. A count of commits was rejected, since the owner rewrites history before publishing and the count would fall.

Encryption. The macOS build links no TLS; cargo tree finds only sha2 and chacha20, used for hashing and random numbers, which are exempt. ITSAppUsesNonExemptEncryption is false, so App Store Connect does not ask at every upload.

Extended attributes are stripped before signing. The first upload was refused with error 91109: Contents/embedded.provisionprofile carried com.apple.quarantine, which the browser set on the downloaded profile and cp kept. xattr -cr on the app before signing removes it and anything else a copied file brings. com.apple.provenance stays on every file, since macOS sets it on whatever an app writes and it cannot be cleared; App Store Connect's check names only quarantine.

Evidence, make appstore on the development Mac:

  • lipo -archs: x86_64 arm64 for both executables, once x86_64-apple-darwin was installed.
  • codesign -dvv: both signed by "Apple Distribution: James Coleman (8XMLMKNPUT)" with the hardened runtime. The app's entitlements are the sandbox list plus 8XMLMKNPUT.com.mrgeckosmedia.MidiHarbor and 8XMLMKNPUT. The helper's are the sandbox and inherit.
  • Contents/embedded.provisionprofile present; codesign --verify --deep --strict passes.
  • pkgutil --check-signature: signed by "3rd Party Mac Developer Installer: James Coleman (8XMLMKNPUT)", which it reports as a development certificate, as it does every App Store installer certificate.

Not checked: an upload after the quarantine fix; the expanded package carries no attribute but com.apple.provenance.

R-110: What App Review's automated check refused

Status: VERIFIED (2026-10-03) locally; resubmitted the same day, verdict pending. Built as T255.

The first submission came back with two automated messages before any person reviewed it.

The private API was winit's. The check named _CGSSetWindowBackgroundBlurRadius. Nothing in this project calls it: winit's macOS backend does, in set_blur, with CGSMainConnectionID beside it, and libcosmic's iced pins pop-os/winit at 9567503. No window here asks for blur, but the linker keeps the import whether or not the call is reached, and the check reads imports. winit 0.30.13 and the fork's other revisions in the cargo cache carry the same call, so no update removes it.

Decision: grmrgecko/winit, branch no-private-blur, is 9567503 with the two declarations removed and set_blur doing nothing on macOS. The root Cargo.toml patches every winit crate to it, since patching winit-appkit alone would leave two copies of winit-core. It moves with the libcosmic revision. The direct-download build takes the same patch, having no use for blur either. bundle.sh now refuses to sign an App Store bundle whose executables import any _CGS followed by a capital, the prefix of the window server's private calls; the public CGShieldingWindowLevel does not match.

The server entitlement stays. The second message said com.apple.security.network.server had no matching functionality. It has: each network port binds UDP ports and takes session invitations from other machines (R-097). The helper does the listening and carries only the sandbox and inherit, which is the likely reason the check saw none, though Apple does not say. The answer is a reply and a note in App Review Information describing RTP-MIDI and how to see a port from Audio MIDI Setup on another Mac, not a change to the build.

Evidence, make appstore on the development Mac:

  • Before, nm -u on the full binary listed _CGSMainConnectionID and _CGSSetWindowBackgroundBlurRadius for both architectures; the headless binary listed neither.
  • After, nm -u -arch arm64 and -arch x86_64 list no _CGS private symbol in either executable, and strings finds no CGSSetWindowBackgroundBlurRadius in the app.
  • codesign --verify --deep --strict passes on the bundle.

Not checked: App Review's verdict on the rebuilt package, and its answer to the reply.