search existing tags for default

src/app/manage/tags/mappings/[id]/page.tsx

@@ -1,6 +1,6 @@
 'use client'
 
-import { useEffect, useState, useRef, useCallback } from 'react'
+import { useEffect, useMemo, useState, useRef, useCallback } from 'react'
 import { useParams } from 'next/navigation'
 import type { Tag, TagCategory, ImportedTag, TagMapping, Library } from '@/types'
 
@@ -335,6 +335,19 @@ function ImportedTagRow({
   onMapped: () => void
   onIgnore: () => void
 }) {
+  // Auto-match: if prefix mapping exists, find a tag in that category matching the stripped name
+  const autoMatchedTagId = useMemo(() => {
+    const colonIdx = importedTag.name.indexOf(': ')
+    if (colonIdx <= 0) return ''
+    const prefix = importedTag.name.slice(0, colonIdx).trim().toLowerCase()
+    const mappedCategoryId = prefixMappings[prefix]
+    if (!mappedCategoryId) return ''
+    const strippedName = importedTag.name.slice(colonIdx + 2).trim().toLowerCase()
+    const group = tagsByCategory.find((g) => g.category.id === mappedCategoryId)
+    const match = group?.tags.find((t) => t.name.toLowerCase() === strippedName)
+    return match?.id ?? ''
+  }, [importedTag.name, prefixMappings, tagsByCategory])
+
   const [selectedTagId, setSelectedTagId] = useState('')
   const [saving, setSaving] = useState(false)
   const [error, setError] = useState<string | null>(null)
@@ -343,6 +356,11 @@ function ImportedTagRow({
   const [newTagCategoryId, setNewTagCategoryId] = useState('')
   const [creatingTag, setCreatingTag] = useState(false)
 
+  // Apply auto-match when it changes (e.g. prefix mappings updated)
+  useEffect(() => {
+    if (autoMatchedTagId) setSelectedTagId(autoMatchedTagId)
+  }, [autoMatchedTagId])
+
   const startCreating = () => {
     // Apply prefix mapping defaults if the imported tag has a colon prefix
     const colonIdx = importedTag.name.indexOf(': ')