feat: request persistent storage to prevent browser eviction of cached AI models

Author: ijbo

changelogs/CHANGELOG-persistent-storage.md

@@ -0,0 +1,24 @@
+# Persistent Storage for Cached AI Models
+
+## Summary
+
+Added `navigator.storage.persist()` request when downloading local AI models, preventing the browser from silently evicting cached model files under storage pressure.
+
+## Changes
+
+### Modified: `js/ai-assistant.js`
+- Made consent download handler `async`
+- Added `navigator.storage.persist()` call before `initAiWorker()`
+- Wrapped in try/catch — non-critical, download proceeds regardless
+- Logs result to console (`💾 Persistent storage granted` / `⚠️ ... not granted`)
+
+## Impact
+
+- **Chrome**: Auto-grants persistent storage for frequently-visited sites and installed PWAs
+- **Firefox**: May show a one-time user prompt
+- **Safari**: Supports the API; behavior varies
+- Prevents browsers from garbage-collecting cached models (80 MB – 2.7 GB) when disk space is low
+
+| File | Changes |
+|------|---------|
+| `js/ai-assistant.js` | +11 −1 |

js/ai-assistant.js

@@ -587,13 +587,23 @@
     });
   }
 
-  aiConsentDownload.addEventListener('click', () => {
+  aiConsentDownload.addEventListener('click', async () => {
     const targetModel = _consentTargetModel || currentAiModel;
     aiConsentDownload.disabled = true;
     aiConsentDownload.innerHTML = '<span class="ai-status-spinner"></span> Loading...';
     aiProgressSection.style.display = 'block';
     localStorage.setItem(M.KEYS.AI_CONSENTED_PREFIX + targetModel, 'true');
     if (targetModel === 'qwen-local') localStorage.setItem(M.KEYS.AI_CONSENTED, 'true');
+
+    // Request persistent storage so the browser won't auto-evict cached models
+    // under storage pressure. Chrome auto-grants for frequent sites; Firefox prompts.
+    try {
+      if (navigator.storage && navigator.storage.persist) {
+        const granted = await navigator.storage.persist();
+        console.log(granted ? '💾 Persistent storage granted — cached models are safe' : '⚠️ Persistent storage not granted — models may be evicted');
+      }
+    } catch (e) { /* non-critical */ }
+
     initAiWorker(targetModel);
   });