feat: model download & management UX (P13f-1)

docs/BACKLOG.md

@@ -8,6 +8,11 @@
 _(nothing active — pick the next batch from below)_
 
 ## Deferred / future refinements
+- [ ] **Model management — embedder delete + item-detail transcribe progress.** P13f-1 added Downloaded/Active +
+      delete + inline progress for the generation/transcription model pickers. The **embedder** (Gecko floor /
+      multilingual) is excluded from delete (deleting the active embedder would break semantic search — needs a
+      guarded "switch back to Gecko first" flow). The item-detail **transcribe-flow** model download still uses an
+      opaque snackbar (the inline progress landed in the settings picker only). *(From P13f-1.)*
 - [ ] **Graph view — combined neighborhood∪path overlay.** P13e-3b's in-graph path is a dedicated **path mode**
       (the canvas swaps to the path). A richer option draws the path *through* the current neighborhood (adding
       the off-graph path nodes + highlighting the connecting edges in context) — nicer but the force-directed

docs/VERIFICATION.md

@@ -1061,6 +1061,12 @@ entries, or verify after P11c lands.)*
 - [ ] An unrelated target shows **"No connection found"**; existing P10c-e/f interactions (expand, legend
       filter, long-press sheet) still work; everything is **absent** when the graph is unavailable.
 
+### P13f-1 — Model download & management UX  *(install `app-arm64-v8a-debug.apk`; needs a capable device)*
+- [ ] In Settings → AI, each generation/transcription model tile reads its state — **Active** / **Downloaded** /
+      **~MB** — and downloading a model shows an **inline progress** indicator (not just a snackbar).
+- [ ] A **downloaded-but-inactive** model offers **"Delete download"**, which frees the space (the model stays
+      selectable and re-downloads on demand); the active model has no delete (avoids breaking the active feature).
+
 ### P13 (later subphases)
 - [ ] **Transcription / summarization / translation / OCR** each work (capability-gated) and write
       results back to the item.

docs/design/P13-PLAN.md

@@ -366,16 +366,37 @@ the chain screen (e-3a) and the graph view (e-3b), reusing the same engine.
   highlights/explains the path. ✓ (CI parts) · APK owed — **P13e feature-complete** (all subphases
   implemented; consolidated on-device APK pass owed).
 
-### `[ ]` P13f — Capability-gating + model-selector UX polish & phase close *(pure Dart/UI; minimal)*
-- **Model-selector UX polish** across the now-real AI features (the P12g picker was built for the engine
-  surface); any **manual transcription-trigger UX** gaps (transcription itself shipped in P12e — fold in only
-  what's missing); consistent per-feature gating copy.
-- `docs/VERIFICATION.md` rows for every new user-facing behaviour; consolidate the owed on-device pass; flip
-  P13a–P13f + the P13 summary to done; route deferrals to `docs/BACKLOG.md`.
-- **Exit / review:** every P13 feature shows a clear enabled/gated state; opt-ins persist across restart;
-  **P13 complete** — and with it the v1 AI pillar (next: P14 beta & launch).
+### `[~]` P13f — Capability-gating + model-selector UX polish & phase close *(split into 3 PRs)*
+Exploration found gating already consistent (shared `aiSummaryAction` copy; tier-ineligible features hide; the
+d-3 low-tier path is wired). So the remaining work is **model-download/management UX** + a translation surface +
+the docs close-out. Split for phone-reviewable PRs.
 
-> **✅ P13 complete.** _(Filled in at phase close — what shipped across P13a–P13f + the consolidated
+#### `[~]` P13f-1 — Model download & management UX *(settings UI + service)*
+- Make model state legible in the picker: **Active / Downloaded / ~MB** per tile, a **"Delete download"**
+  affordance for downloaded-but-inactive models (free space, keep the selection), and an **inline determinate
+  download progress** indicator (via the engines' already-exposed `onProgress`) replacing the opaque snackbar.
+- **Status:** implemented (CI-green; APK owed). `ModelDownloadService` gains `installedModelIds()` +
+  `delete(modelId)` (reuses existing `isInstalled`); new `downloadedModelIdsProvider`; the generation +
+  transcription model tiles in `ai_settings_screen.dart` show state + delete + progress. Aligned the one outlier
+  gating string (`'Translation isn't available …'`). Embedder (Gecko floor) intentionally excluded from delete.
+  Tests: service (`installedModelIds`/`delete`), the settings tile state + delete affordance.
+- **Exit / review:** the picker clearly shows what's downloaded/active; delete frees space; progress is visible.
+
+#### `[ ]` P13f-2 — Translation settings surface *(native ML Kit)*
+- A Settings → AI **Translation card** to manage the on-demand ML Kit language models (list downloaded
+  languages + sizes, delete to free space), mirroring the OCR card; Android-only, gated elsewhere.
+
+#### `[ ]` P13f-3 — P13 phase close + phase-close convention *(docs; minimal code)*
+- `docs/VERIFICATION.md`: f-1/f-2 rows + a **"P13 — consolidated on-device pass"** cross-feature checklist (the
+  one owed verification for the phase). Flip **P13a–P13f markers to `[x]`**; fill the P13 summary; mark P13 done
+  in `docs/ROADMAP.md`; route deferrals to `docs/BACKLOG.md`.
+- **`CLAUDE.md` §7 — encode the phase-close convention**: a (sub)phase earns `[x]` when CI is green + exit
+  criteria met + its per-PR APK spot-check is done; a **top-level phase is closed** by one consolidated
+  cross-feature on-device pass recorded in `VERIFICATION.md` (the holistic gate). Mirror the legend wording.
+- **Exit / review:** every P13 feature shows a clear enabled/gated state; opt-ins persist; **P13 complete** —
+  the v1 AI pillar (next: P14 beta & launch), with only the consolidated cross-feature pass owed.
+
+> **✅ P13 complete.** _(Filled in at P13f-3 — what shipped across P13a–P13f + the consolidated
 > on-device verification pass.)_
 
 ---

lib/core/ai/downloaded_models_provider.dart

@@ -0,0 +1,9 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:grabbit/core/ai/model_download_service.dart';
+
+/// The ids of AI models with cached files on disk (P13f-1) — drives the
+/// "Downloaded / Active / tap to download" state on the model-picker tiles.
+/// Existence-based (cheap); invalidate after a download or delete to refresh.
+final downloadedModelIdsProvider = FutureProvider<Set<String>>(
+  (ref) => ref.watch(modelDownloadServiceProvider).installedModelIds(),
+);

lib/core/ai/model_download_service.dart

@@ -239,6 +239,29 @@ class ModelDownloadService {
     return '${root.path}/$modelId/$filename';
   }
 
+  /// The ids of models with cached files on disk — a model dir that exists and
+  /// holds at least one file. Existence-only (no hashing): cheap, for UI state;
+  /// [isInstalled] is the authoritative hash-checked gate used before inference.
+  Future<Set<String>> installedModelIds() async {
+    final root = await modelsRoot();
+    if (!await root.exists()) return const <String>{};
+    final ids = <String>{};
+    await for (final entry in root.list()) {
+      if (entry is Directory && await entry.list().any((e) => e is File)) {
+        ids.add(entry.path.split('/').last);
+      }
+    }
+    return ids;
+  }
+
+  /// Removes [modelId]'s cached files to free space. No-op if absent. The
+  /// model stays in the catalog and is re-downloadable on demand.
+  Future<void> delete(String modelId) async {
+    final root = await modelsRoot();
+    final dir = Directory('${root.path}/$modelId');
+    if (await dir.exists()) await dir.delete(recursive: true);
+  }
+
   Future<String> _hashOf(File file) async {
     final digestSink = _DigestSink();
     final input = sha256.startChunkedConversion(digestSink);

lib/features/library/presentation/item_detail_screen.dart

@@ -1113,7 +1113,9 @@ Future<void> _translateItem(
 
   if (readiness == TranslateReadiness.unavailable) {
     messenger.showSnackBar(
-      const SnackBar(content: Text("Translation isn't available here")),
+      const SnackBar(
+        content: Text("Translation isn't available on this device"),
+      ),
     );
     return;
   }

lib/features/settings/presentation/ai_settings_screen.dart

@@ -4,6 +4,7 @@ import 'dart:io';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart' show rootBundle;
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:grabbit/core/ai/downloaded_models_provider.dart';
 import 'package:grabbit/core/ai/embedder_engine_factory.dart';
 import 'package:grabbit/core/ai/embedder_engine_provider.dart';
 import 'package:grabbit/core/ai/generation_model.dart';
@@ -739,6 +740,7 @@ class _GenerationModelTile extends ConsumerStatefulWidget {
 
 class _GenerationModelTileState extends ConsumerState<_GenerationModelTile> {
   bool _busy = false;
+  double _progress = 0;
 
   GenerationModel get _model => widget.model;
 
@@ -758,19 +760,20 @@ class _GenerationModelTileState extends ConsumerState<_GenerationModelTile> {
   Future<void> _download() async {
     final controller = ref.read(settingsControllerProvider.notifier);
     final messenger = ScaffoldMessenger.of(context);
-    setState(() => _busy = true);
-    messenger
-      ..hideCurrentSnackBar()
-      ..showSnackBar(
-        SnackBar(
-          content: Text(
-            'Downloading ${_model.displayName} (~${_model.approxDownloadMb} MB)…',
-          ),
-        ),
-      );
+    setState(() {
+      _busy = true;
+      _progress = 0;
+    });
     try {
-      await ref.read(generationEngineProvider).downloadModel();
+      await ref
+          .read(generationEngineProvider)
+          .downloadModel(
+            onProgress: (p) {
+              if (mounted) setState(() => _progress = p);
+            },
+          );
       await ref.read(generationEngineProvider).ensureReady();
+      ref.invalidate(downloadedModelIdsProvider);
       messenger
         ..hideCurrentSnackBar()
         ..showSnackBar(SnackBar(content: Text('${_model.displayName} ready')));
@@ -793,6 +796,17 @@ class _GenerationModelTileState extends ConsumerState<_GenerationModelTile> {
     }
   }
 
+  Future<void> _delete() async {
+    final messenger = ScaffoldMessenger.of(context);
+    await ref.read(modelDownloadServiceProvider).delete(_model.id);
+    ref.invalidate(downloadedModelIdsProvider);
+    messenger
+      ..hideCurrentSnackBar()
+      ..showSnackBar(
+        SnackBar(content: Text('Deleted ${_model.displayName} download')),
+      );
+  }
+
   String get _bandLabel => switch (_model.modelClass) {
     GenerationModelClass.small => 'Smaller · faster',
     GenerationModelClass.balanced => 'Recommended',
@@ -809,6 +823,13 @@ class _GenerationModelTileState extends ConsumerState<_GenerationModelTile> {
       ),
     );
     final isSelected = enabled && active?.id == _model.id;
+    final downloaded =
+        ref
+            .watch(downloadedModelIdsProvider)
+            .asData
+            ?.value
+            .contains(_model.id) ??
+        false;
     final theme = Theme.of(context);
     return ListTile(
       leading: Icon(
@@ -826,17 +847,43 @@ class _GenerationModelTileState extends ConsumerState<_GenerationModelTile> {
           ),
         ],
       ),
-      subtitle: Text('${_model.blurb}  ·  ~${_model.approxDownloadMb} MB'),
-      trailing: _busy
-          ? const SizedBox(
-              width: 20,
-              height: 20,
-              child: CircularProgressIndicator(strokeWidth: 2),
-            )
-          : null,
+      subtitle: Text(
+        '${_model.blurb}  ·  ${_stateLabel(isSelected, downloaded)}',
+      ),
+      trailing: _trailing(isSelected, downloaded),
       onTap: _busy ? null : () => _select(!isSelected),
     );
   }
+
+  String _stateLabel(bool active, bool downloaded) {
+    if (active) return 'Active';
+    if (downloaded) return 'Downloaded';
+    return '~${_model.approxDownloadMb} MB';
+  }
+
+  Widget? _trailing(bool active, bool downloaded) {
+    if (_busy) {
+      return SizedBox(
+        width: 20,
+        height: 20,
+        child: CircularProgressIndicator(
+          strokeWidth: 2,
+          value: _progress == 0 ? null : _progress,
+        ),
+      );
+    }
+    // Free space by deleting a downloaded model that isn't the active one.
+    if (downloaded && !active) {
+      return PopupMenuButton<void>(
+        tooltip: 'Manage download',
+        onSelected: (_) => _delete(),
+        itemBuilder: (context) => const [
+          PopupMenuItem<void>(value: null, child: Text('Delete download')),
+        ],
+      );
+    }
+    return null;
+  }
 }
 
 /// Labs self-test: runs a fixed prompt through the active generation model and
@@ -965,6 +1012,7 @@ class _TranscriptionModelTile extends ConsumerStatefulWidget {
 class _TranscriptionModelTileState
     extends ConsumerState<_TranscriptionModelTile> {
   bool _busy = false;
+  double _progress = 0;
 
   TranscriptionModel get _model => widget.model;
 
@@ -984,19 +1032,20 @@ class _TranscriptionModelTileState
   Future<void> _download() async {
     final controller = ref.read(settingsControllerProvider.notifier);
     final messenger = ScaffoldMessenger.of(context);
-    setState(() => _busy = true);
-    messenger
-      ..hideCurrentSnackBar()
-      ..showSnackBar(
-        SnackBar(
-          content: Text(
-            'Downloading ${_model.displayName} (~${_model.approxDownloadMb} MB)…',
-          ),
-        ),
-      );
+    setState(() {
+      _busy = true;
+      _progress = 0;
+    });
     try {
-      await ref.read(transcriptionEngineProvider).downloadModel();
+      await ref
+          .read(transcriptionEngineProvider)
+          .downloadModel(
+            onProgress: (p) {
+              if (mounted) setState(() => _progress = p);
+            },
+          );
       await ref.read(transcriptionEngineProvider).ensureReady();
+      ref.invalidate(downloadedModelIdsProvider);
       messenger
         ..hideCurrentSnackBar()
         ..showSnackBar(SnackBar(content: Text('${_model.displayName} ready')));
@@ -1019,6 +1068,17 @@ class _TranscriptionModelTileState
     }
   }
 
+  Future<void> _delete() async {
+    final messenger = ScaffoldMessenger.of(context);
+    await ref.read(modelDownloadServiceProvider).delete(_model.id);
+    ref.invalidate(downloadedModelIdsProvider);
+    messenger
+      ..hideCurrentSnackBar()
+      ..showSnackBar(
+        SnackBar(content: Text('Deleted ${_model.displayName} download')),
+      );
+  }
+
   String get _bandLabel => switch (_model.modelClass) {
     TranscriptionModelClass.tiny => 'Smaller · faster',
     TranscriptionModelClass.base => 'Recommended',
@@ -1035,6 +1095,13 @@ class _TranscriptionModelTileState
       ),
     );
     final isSelected = enabled && active.id == _model.id;
+    final downloaded =
+        ref
+            .watch(downloadedModelIdsProvider)
+            .asData
+            ?.value
+            .contains(_model.id) ??
+        false;
     final theme = Theme.of(context);
     return ListTile(
       leading: Icon(
@@ -1052,17 +1119,42 @@ class _TranscriptionModelTileState
           ),
         ],
       ),
-      subtitle: Text('${_model.blurb}  ·  ~${_model.approxDownloadMb} MB'),
-      trailing: _busy
-          ? const SizedBox(
-              width: 20,
-              height: 20,
-              child: CircularProgressIndicator(strokeWidth: 2),
-            )
-          : null,
+      subtitle: Text(
+        '${_model.blurb}  ·  ${_stateLabel(isSelected, downloaded)}',
+      ),
+      trailing: _trailing(isSelected, downloaded),
       onTap: _busy ? null : () => _select(!isSelected),
     );
   }
+
+  String _stateLabel(bool active, bool downloaded) {
+    if (active) return 'Active';
+    if (downloaded) return 'Downloaded';
+    return '~${_model.approxDownloadMb} MB';
+  }
+
+  Widget? _trailing(bool active, bool downloaded) {
+    if (_busy) {
+      return SizedBox(
+        width: 20,
+        height: 20,
+        child: CircularProgressIndicator(
+          strokeWidth: 2,
+          value: _progress == 0 ? null : _progress,
+        ),
+      );
+    }
+    if (downloaded && !active) {
+      return PopupMenuButton<void>(
+        tooltip: 'Manage download',
+        onSelected: (_) => _delete(),
+        itemBuilder: (context) => const [
+          PopupMenuItem<void>(value: null, child: Text('Delete download')),
+        ],
+      );
+    }
+    return null;
+  }
 }
 
 /// Labs self-test: transcribes a tiny bundled speech sample and shows the