send higher resolution images to AI vision endpoints

Add getAiImagePath() to thumbnails.ts (1920px wide, quality 90, no
upscaling) cached separately from display thumbnails via an _ai suffix.
Swap all four image-to-AI code paths in ai-tagger.ts (extract text,
describe, batch tagging x2) to use the new high-res image instead of
the 400px display thumbnail, improving OCR accuracy on dense text.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/ai-tagger.ts

@@ -4,7 +4,7 @@ import type { Library, Tag, TagCategory } from '@/types'
 import { getDb } from './db'
 import { getAiConfig, getEffectiveAiConfig, getPreferredLanguage } from './app-settings'
 import { getTags, getCategories, addTagToItem, getActiveCategoryIdsForLibrary, getResolvedTagsForItem } from './tags'
-import { getThumbnailPath, getVideoFramePaths } from './thumbnails'
+import { getAiImagePath, getVideoFramePaths } from './thumbnails'
 import { findFile } from './media-utils'
 import { getLibrary, resolveLibraryRoot } from './libraries'
 
@@ -279,7 +279,7 @@ export async function runAiTagging(library: Library, libraryRoot: string): Promi
         const framePaths = await getVideoFramePaths(resolvedMedia.path, library.id, VIDEO_FRAME_PERCENTAGES)
         base64Images = framePaths.map((p) => fs.readFileSync(p, 'base64'))
       } else {
-        const thumbnailPath = await getThumbnailPath(resolvedMedia.path, library.id, 'image')
+        const thumbnailPath = await getAiImagePath(resolvedMedia.path, library.id)
         base64Images = [fs.readFileSync(thumbnailPath, 'base64')]
       }
 
@@ -367,7 +367,7 @@ export async function tagSingleItem(itemKey: string): Promise<string[]> {
     const framePaths = await getVideoFramePaths(imagePath.path, libraryId, VIDEO_FRAME_PERCENTAGES)
     base64Images = framePaths.map((p) => fs.readFileSync(p, 'base64'))
   } else {
-    const thumbnailPath = await getThumbnailPath(imagePath.path, libraryId, 'image')
+    const thumbnailPath = await getAiImagePath(imagePath.path, libraryId)
     base64Images = [fs.readFileSync(thumbnailPath, 'base64')]
   }
 
@@ -529,7 +529,7 @@ export async function generateItemDescription(itemKey: string): Promise<string>
     const framePaths = await getVideoFramePaths(resolvedMedia.path, libraryId, VIDEO_FRAME_PERCENTAGES)
     base64Images = framePaths.map((p) => fs.readFileSync(p, 'base64'))
   } else {
-    const thumbnailPath = await getThumbnailPath(resolvedMedia.path, libraryId, 'image')
+    const thumbnailPath = await getAiImagePath(resolvedMedia.path, libraryId)
     base64Images = [fs.readFileSync(thumbnailPath, 'base64')]
   }
 
@@ -587,7 +587,7 @@ export async function extractItemText(itemKey: string): Promise<{ extractedText:
     throw Object.assign(new Error('Text extraction is only available for images'), { code: 'NO_IMAGE' })
   }
 
-  const thumbnailPath = await getThumbnailPath(resolvedMedia.path, libraryId, 'image')
+  const thumbnailPath = await getAiImagePath(resolvedMedia.path, libraryId)
   const base64Images = [fs.readFileSync(thumbnailPath, 'base64')]
 
   const systemPrompt = `You are an OCR assistant. Extract ALL text visible in the image exactly as it appears. Preserve line breaks and formatting.${config.promptExtract ? ' ' + config.promptExtract : ''} If there is no text in the image, respond with exactly: [NO TEXT]`

src/lib/thumbnails.ts

@@ -7,6 +7,8 @@ import sharp from 'sharp'
 const CACHE_DIR = path.resolve(process.cwd(), '.thumbnails')
 const THUMBNAIL_WIDTH = 400
 const JPEG_QUALITY = 75
+const AI_IMAGE_WIDTH = 1920
+const AI_JPEG_QUALITY = 90
 
 /** Ensure the cache directory exists. */
 function ensureCacheDir(): void {
@@ -47,6 +49,17 @@ async function generateImageThumbnail(src: string, dest: string): Promise<void>
   fs.renameSync(tmp, dest)
 }
 
+/** Generate a high-resolution JPEG for AI vision use. Images smaller than
+ *  AI_IMAGE_WIDTH are not upscaled — they are converted at their native size. */
+async function generateAiImage(src: string, dest: string): Promise<void> {
+  const tmp = dest + '.tmp'
+  await sharp(src)
+    .resize(AI_IMAGE_WIDTH, undefined, { withoutEnlargement: true })
+    .jpeg({ quality: AI_JPEG_QUALITY })
+    .toFile(tmp)
+  fs.renameSync(tmp, dest)
+}
+
 /** Run a child process and collect stderr. Resolves on exit code 0, rejects otherwise. */
 function run(bin: string, args: string[]): Promise<void> {
   return new Promise((resolve, reject) => {
@@ -158,6 +171,25 @@ export async function getVideoFramePaths(
   return framePaths
 }
 
+/**
+ * Returns the absolute path to a high-resolution JPEG suitable for AI vision
+ * APIs (1920px wide max, quality 90). Cached alongside display thumbnails with
+ * an `_ai` suffix so display performance is unaffected.
+ * Generates on first call or when the source file has been modified.
+ */
+export async function getAiImagePath(
+  absoluteFilePath: string,
+  libraryId: string
+): Promise<string> {
+  ensureCacheDir()
+  const key = cacheKey(libraryId, absoluteFilePath)
+  const cacheFile = path.join(CACHE_DIR, key + '_ai.jpg')
+  const cached = getCachedPath(cacheFile, absoluteFilePath)
+  if (cached) return cached
+  await generateAiImage(absoluteFilePath, cacheFile)
+  return cacheFile
+}
+
 /**
  * Returns the absolute path to a cached thumbnail JPEG for the given file.
  * Generates it on first call (or when the source has been modified).