File Provider extension cannot access App Group container despite identical entitlement

I have a Tauri/Rust application with a native Swift File Provider extension. Both are configured to use the same App Group, but the extension cannot access the shared continer at all - it can't even list contents or create files. Getting "Operation not permitted" despite all configurations appearing correct. The Rust side manages the database (used on Windows/Linux/macOS), while the File Provider extension needs read access to display files in Finder.

Architecture:

• Main app: Tauri/Rust creates SQLite database
• Extension: Swift File Provider needs read access
• Communication: App Groups shared container
• Rust -> Swift via @_cdecl FFI to get container path

Current Configuration:

• Same Team ID (UF927XXXXX) for both
• Same App Group (group.com.domain.files)
• Both sandboxed with identical entitlements
• File permissions: -rw-rw-rw- (no ACL)
• Code signing valid
• Paths identical: /Users/user/Library/Group Containers/group.com.domain.files/files.sqlite

The Problem:

Extension loads but cannot access container - fails on all operations with "Operation not permitted". The extension can't even list the container contents.

What I've Verified:

• ✅ Entitlements match
• ✅ Team IDs match
• ✅ App Groups identical
• ✅ Sandbox enabled for both
• ✅ Code signing valid
• ✅ File exists with correct permissions

Both Entitlements have this content:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>com.apple.security.app-sandbox</key>
    <true/>
    <key>com.apple.security.application-groups</key>
    <array>
        <string>group.com.domain.files</string>
    </array>
    <key>com.apple.security.files.user-selected.read-write</key>
    <true/>
</dict>
</plist>

Swift Plugin - Get Container Path (called from Rust):

@_cdecl("swift_get_app_group_path")
public func getAppGroupPath() -> UnsafePointer<CChar>? {
    guard let containerURL = FileManager.default.containerURL(
        forSecurityApplicationGroupIdentifier: "group.com.domain.files"
    ) else {
        return nil
    }
    return UnsafePointer(strdup(containerURL.path))
}

Swift Extension - Debug Access (showing failures):

func testContainerAccess() {
    guard let container = FileManager.default.containerURL(
        forSecurityApplicationGroupIdentifier: "group.com.domain.files"
    ) else {
        print("❌ Cannot get container URL")
        return
    }
    
    print("📍 Container path: \(container.path)")
    
    // Test 1: List contents
    do {
        let contents = try FileManager.default.contentsOfDirectory(atPath: container.path)
        print("✅ Can list container: \(contents)")
    } catch {
        print("❌ Cannot list container: \(error)")
    }
    
    // Test 2: Check if DB file exists
    let dbURL = container.appendingPathComponent("files.sqlite")
    if FileManager.default.fileExists(atPath: dbURL.path) {
        print("✅ DB file exists")
    } else {
        print("❌ DB file missing")
    }
    
    // Test 3: Try to read DB file
    do {
        let data = try Data(contentsOf: dbURL)
        print("✅ Can read DB file, size: \(data.count)")
    } catch {
        print("❌ Cannot read DB file: \(error)")
    }
    
    // Test 4: Try SQLite open
    var db: OpaquePointer?
    if sqlite3_open_v2(dbURL.path, &db, SQLITE_OPEN_READONLY, nil) == SQLITE_OK {
        print("✅ SQLite can open database")
        sqlite3_close(db)
    } else {
        let error = String(cString: sqlite3_errmsg(db))
        print("❌ SQLite open failed: \(error)")
        sqlite3_close(db)
    }
}

Swift Extension - Info.plist (File Provider config):

<key>NSExtension</key>
<dict>
    <key>NSExtensionFileProviderDocumentGroup</key>
    <string>group.com.domain.files</string>
    <key>NSExtensionPointIdentifier</key>
    <string>com.apple.fileprovider-nonui</string>
    <key>NSExtensionPrincipalClass</key>
    <string>$(PRODUCT_MODULE_NAME).FileProviderExtension</string>
</dict>

Environment:

• macOS Tahoe (26.0)
• Local signing (no Apple Developer account)
• Xcode