Friendly loading-error messages + rotating debug log

[Adron]

What

Loading failures were showing raw technical text from APIError (e.g. "Decoding ListRowDTO failed: keyNotFound…"). This makes the UI friendly and moves the technical detail into a retrievable debug-log file.

User-facing messages (fix at the error type)

• APIError.errorDescription (→ localizedDescription, which every error banner already reads) now returns a new userFacingMessage — friendly copy for the client-only cases (decoding / transport / bare status codes). Server-written 4xx messages (e.g. "Email not verified") are preserved verbatim.
• The technical string stays in .description (used only for logs). Net effect: every existing banner improves with no view-file edits.

Debug log in the app's folder

• New AppLog (facade over os.Logger) + rotating FileLog → ~/Library/Containers/com.interlinedlist.macos/Data/Library/Logs/InterlinedList/interlinedlist.log (5 MB rotation, one .1 backup).
• APIClient logs the full technical cause — request path + complete DecodingError coding path — at every decode / transport / non-2xx failure. The user only ever sees the friendly banner.

Example log line produced end-to-end:

… [ERROR] APIClient: Decode failed [/api/x] type=Greeting: DecodingError.dataCorrupted … Unexpected character 'n' around line 1, column 3 …

Testing

• 282 InterlinedKit tests pass (7 new: user-facing/technical split, FileLog write + rotation + no-op).
• A test-isolation guard sniffs the loaded XCTestCase runtime (SwiftPM omits XCTestConfigurationFilePath) so unit runs never write to the real ~/Library.
• App builds (** BUILD SUCCEEDED **).

Notes

• Retrieval is file-on-disk for now; a Help-menu "Reveal/Export Logs…" affordance can follow.
• Covers everything through APIClient (all network/decoding errors); domain errors were already friendly.

🤖 Generated with Claude Code