Improve chat app model and mmproj cache UX

[leehack]

Summary

Improves the chat app model/mmproj cache UX for issue #132:

• tracks model and mmproj cache state independently
• surfaces partial cache state in Manage Models and model cards
• downloads/caches only missing assets when a profile is partially cached
• refreshes all cache states after download/delete so shared assets do not leave stale cards
• persists web cache markers per asset as each prefetch succeeds
• warns before saving signed/tokenized custom model URLs

Fixes #132.

Validation

• flutter analyze --no-pub passed in example/chat_app
• flutter test --no-pub test/model_card_test.dart test/model_service_test.dart test/manage_models_screen_download_test.dart test/model_download_controller_adapter_test.dart test/unit_test.dart passed
• additional focused tests after review fixes passed:
  • flutter test test/model_service_test.dart test/model_card_test.dart test/model_download_controller_adapter_test.dart test/model_asset_source_test.dart test/manage_models_screen_download_test.dart
• git diff --check passed
• Real chat-app E2E passed on macOS:
  • dart run tool/testing/run_local_e2e.dart --scenario chat-app-model-cache --device macos
  • built the macOS app, downloaded real LFM2-VL model + mmproj, loaded through ChatService, and asserted engine ready plus supportsVision == true

Notes

The macOS E2E emitted a non-fatal Failed to foreground app; open returned 1 warning after all tests had already passed.

[github-actions]

Chat app preview removed for leehack/llamadart-chat-pr-266.

[Copilot]

Pull request overview

This PR improves the runnable chat app’s model + multimodal projector (“mmproj”) caching UX by tracking cache state per asset (model vs projector), enabling partial-cache recovery (download/cache only missing assets), refreshing cache state across all profiles after download/delete, and warning users before persisting signed/tokenized custom Hugging Face URLs.

Changes:

• Introduces per-asset cache state (ModelProfileCacheState) and cache-key markers (ModelAssetCacheMarkers) to represent partial availability.
• Updates IO + Web model services to skip already-cached assets and to persist cache markers per asset as each stage succeeds.
• Enhances Manage Models + ModelCard UI to display model/mmproj cache chips, partial-cache messaging, capability mismatch warnings, and credentialed-URL confirmation.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
CHANGELOG.md	Adds an Unreleased entry describing the chat app cache UX improvements and credentialed-URL confirmation.
website/docs/changelog/recent-releases.md	Mirrors the Unreleased entry for website “Recent Releases”.
example/chat_app/lib/services/model_service_base.dart	Adds getModelCacheState API plus new cache state/marker types for per-asset availability.
example/chat_app/lib/services/model_service_io.dart	Computes per-asset cache state and skips downloading already-present model/mmproj assets.
example/chat_app/lib/services/model_service_web.dart	Migrates cache markers in getDownloadedModels, adds per-asset cache state, and caches only missing web assets while persisting markers per stage.
example/chat_app/lib/screens/manage_models_screen.dart	Refreshes cache state independently of “downloaded” state, warns on runtime capability mismatches, and confirms saving credential-like custom URLs.
example/chat_app/lib/widgets/model_card.dart	Displays asset-level cache chips + partial-cache messaging and adjusts download/delete labels accordingly.
example/chat_app/test/model_service_test.dart	Adds coverage for skipping cached model downloads when only mmproj is missing.
example/chat_app/test/model_card_test.dart	Adds widget coverage for partial multimodal cache UI/UX behavior.
example/chat_app/test/manage_models_screen_download_test.dart	Adds widget coverage for capability mismatch warnings, shared-asset refresh on delete, and credentialed-URL confirmation flow.
example/chat_app/test/model_download_controller_adapter_test.dart	Updates test fake to satisfy the new getModelCacheState API.
example/chat_app/test/model_asset_source_test.dart	Adds unit coverage for cache markers correctly reflecting partial-cache state.
example/chat_app/test/unit_test.dart	Updates recording service stub to implement getModelCacheState.

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