fix(dive-computer): log download failures to the file log

[ericgriffin]

Summary

• DownloadNotifier handled DownloadErrorEvent and caught startDownload exceptions by updating UI state only, never calling the logger. A user reporting "Download failed" on a Shearwater Teric over Windows 11 BLE had no [LDC] or [ERROR] entries in submersion.log, making remote diagnosis impossible.
• Both error paths now emit _log.error(...) under LogCategory.libdc. The Dart catch block also forwards the exception and stack trace; the native DownloadErrorEvent handler logs the error code and message from libdivecomputer.

Why

Without a logged error, a libdc-reported BLE comms failure, a permission error on startDownload, and a "download completed with 0 dives" outcome are all indistinguishable in a user-submitted log. This blocks support triage on exactly the flows most likely to break (BLE dive computers on Windows).

Test plan

• flutter test test/features/dive_computer/presentation/providers/download_notifier_fingerprint_test.dart — 5/5 pass (2 new)
• New tests subscribe to LoggerService.logStream, assert exactly one LogLevel.error entry per failure path with the expected category and message substrings
• Tests verified RED first (assertion hasLength(1) vs []), then GREEN after the fix
• dart format — clean
• flutter analyze — "No issues found"
• Full pre-push suite — 7098 tests passing

[Copilot]

Pull request overview

This PR improves diagnosability of dive-computer download failures by ensuring DownloadNotifier emits LogLevel.error entries under LogCategory.libdc for both plugin error events and Dart-side startDownload exceptions, and adds tests to verify those logs are produced.

Changes:

• Add libdc error logging when startDownload throws (including exception + stack trace).
• Add libdc error logging when a DownloadErrorEvent is received (including error code/message).
• Add tests that subscribe to LoggerService.logStream and assert exactly one error log entry per failure path.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
lib/features/dive_computer/presentation/providers/download_providers.dart	Add _log.error(...) calls for startDownload exceptions and DownloadErrorEvent handling.
test/features/dive_computer/presentation/providers/download_notifier_fingerprint_test.dart	Add tests validating error logs are emitted for both failure paths.

Comments suppressed due to low confidence (1)

lib/features/dive_computer/presentation/providers/download_providers.dart:177

• In the startDownload exception path, the download events subscription has already been created (_service.downloadEvents.listen(...)) but is not cancelled when startDownload throws. This can leave a dangling listener that may continue to receive events and mutate state after an immediate start failure. Cancel and null out _downloadSubscription in the catch block (and consider also calling _service.cancelDownload() if appropriate) to keep state consistent and avoid leaks.

    } catch (e, stackTrace) {
      _log.error(
        'Download failed',
        category: LogCategory.libdc,
        error: e,
        stackTrace: stackTrace,
      );
      state = state.copyWith(
        phase: DownloadPhase.error,
        errorMessage: 'Download failed: $e',
      );
    }

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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