fix(ios): import picker media per-item so one failure doesn't drop the rest

[jkmassel]

Fixes a bug where importing a multi-photo selection in the native block inserter dropped every item after the first one that failed to import — and, when a failure landed alongside a success, surfaced no error at all.

Summary

• The block inserter's photo picker imported a selection in a single do/catch loop, so the first item that failed to import aborted the whole selection — every item after it was skipped.
• The error notice was gated on results.isEmpty, so a failure alongside a success was dropped silently.
• Now each item imports independently: the ones that succeed are inserted, and any failure is surfaced — including a partial failure, which now names how many items were skipped.

Root Cause

BlockInserterViewModel.processSelectedPhotosPickerItems wrapped the entire for loop in one do/catch. A throw from MediaFileManager.import — e.g. a photo not fully downloaded from iCloud, or one too large to materialize into memory — jumped straight to the catch, so items after the failure were never attempted. The if results.isEmpty gate then meant a partial failure showed nothing.

Fix

• BlockInserterViewModel.swift: import each item in its own do/catch, counting failures. After the loop, resolve the alert through a new testable importError(failureCount:successCount:) — the existing "nothing could be loaded" copy when everything failed, or a new count-aware message on a partial failure.
• BlockInserterView.swift: on any failure, insert whatever succeeded and keep the inserter open so its alert is visible. Acknowledging the alert closes the inserter only on a partial success; a total failure leaves it open to retry — unchanged from today.
• EditorLocalization.swift: add someSelectedMediaFailedToLoad(Int) with singular/plural defaults.

Testability

PhotosPickerItem can't be constructed in a test, so the import loop had no direct coverage. A new ImportableMediaItem protocol captures the slice of PhotosPickerItem that MediaFileManager.import uses (supportedContentTypes, loadTransferable); PhotosPickerItem conforms via an empty extension, and import / processSelectedPhotosPickerItems now take some ImportableMediaItem. The view model's MediaFileManager is injectable, so tests drive the real loop with a mock item and a temp-directory file manager. No production behavior change.

Test Plan

• make lint-swift clean on the changed files.
• Swift package builds for the iOS Simulator; unit tests pass. BlockInserterViewModelTests drives the real import loop — partial failure (successes kept, error surfaced), total failure, and full success — plus EditorLocalizationTests.defaultsPluralizeSkippedMediaCounts.
• Device: pick several photos where one isn't fully downloaded from iCloud → the others insert and an alert names the skipped count.
• Device: pick a single unloadable photo → alert shown, inserter stays open to retry.

Notes

• iOS only. Android's native block picker routes picked media through inert callbacks today (editor hand-off is a documented follow-up), so there's no equivalent import loop to change.
• Separate from the WordPress-iOS ItemProviderMediaExporter upload hang: that's the host's Media Library picker, reached via openMediaLibrary → the host delegate — a different code path from this inserter import.

🤖 Generated with Claude Code

[wpmobilebot]

XCFramework Build

This PR's XCFramework is available for testing. Add the following to your Package.swift:

.package(url: "https://github.com/wordpress-mobile/GutenbergKit", branch: "pr-build/623")

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