Rename: Skip extension confirm on case-only changes

- Add `extensionsDifferIgnoringCase` helper in `filename-validation.ts`; both `validateExtensionChange` and the rename save flow's "ask" gate now route through it.
- `photo.JPG` → `photo.jpg` no longer triggers the ExtensionChangeDialog or the red border (when policy is `no`).
- Two unit tests pin the behavior, including a regression guard that real ext changes still error under `no`.

Author: vdavid

apps/desktop/src/lib/file-explorer/rename/CLAUDE.md

@@ -29,9 +29,10 @@ Operates on cursor item only; selection is preserved and irrelevant.
 
 Implemented in `rename-operations.ts::executeRenameSave()`:
 
-1. **Extension check**: If `extensionPolicy === 'ask'` and `getExtension(originalName) !== getExtension(newName)`,
-   return `{ type: 'extension-ask' }`. Caller shows ExtensionChangeDialog. If user clicks "Keep", retry with
-   `skipExtensionCheck=true`.
+1. **Extension check**: If `extensionPolicy === 'ask'` and the extensions differ in more than letter case
+   (`extensionsDifferIgnoringCase()` from `filename-validation.ts`), return `{ type: 'extension-ask' }`. Caller shows
+   ExtensionChangeDialog. If user clicks "Keep", retry with `skipExtensionCheck=true`. Case-only changes like
+   `photo.JPG` → `photo.jpg` skip the dialog entirely.
 
 2. **Backend validity check**: Call `checkRenameValidity(parentPath, originalName, trimmedName)`. Returns:
    - `{ valid: false, error }` → return `{ type: 'error' }`
@@ -115,7 +116,8 @@ trimmed value.
 - **Cancel triggers**: Escape, click elsewhere, Tab, drag start, scroll >200px cumulative, sort/hidden toggle all
   discard rename. File watcher events during editing don't cancel (backend will catch issues on save).
 - **Extension validation gotcha**: If setting is "no", changing extension shows red border during editing. If setting is
-  "ask", no red border (waits for save to show dialog). If setting is "yes", never validates extension.
+  "ask", no red border (waits for save to show dialog). If setting is "yes", never validates extension. Case-only
+  extension changes (e.g. `.JPG` → `.jpg`) are treated as no change in all modes.
 - **Same-name edge case**: If `trimmedName === originalName`, treat as cancel (no-op). Don't emit file watcher event or
   refresh pane. Avoids spurious refresh on whitespace-only edits.
 - **Click-to-rename interference**: Double-click on name area must open file/folder (normal behavior), not activate

apps/desktop/src/lib/file-explorer/rename/rename-operations.ts

@@ -4,7 +4,7 @@
  * except for the actual backend calls which are awaited.
  */
 
-import { getExtension } from '$lib/utils/filename-validation'
+import { extensionsDifferIgnoringCase, getExtension } from '$lib/utils/filename-validation'
 
 export interface ConflictFileInfo {
   name: string
@@ -49,16 +49,16 @@ export async function executeRenameSave(
     return { type: 'noop' }
   }
 
-  // Check extension change
-  if (!skipExtensionCheck) {
-    const oldExt = getExtension(target.originalName)
-    const newExt = getExtension(trimmedName)
-    if (oldExt !== newExt && extensionPolicy === 'ask') {
-      return {
-        type: 'extension-ask',
-        oldExtension: oldExt.replace(/^\./, ''),
-        newExtension: newExt.replace(/^\./, ''),
-      }
+  // Check extension change (case-only changes are silently allowed)
+  if (
+    !skipExtensionCheck &&
+    extensionPolicy === 'ask' &&
+    extensionsDifferIgnoringCase(target.originalName, trimmedName)
+  ) {
+    return {
+      type: 'extension-ask',
+      oldExtension: getExtension(target.originalName).replace(/^\./, ''),
+      newExtension: getExtension(trimmedName).replace(/^\./, ''),
     }
   }
 

apps/desktop/src/lib/utils/CLAUDE.md

@@ -62,6 +62,9 @@ interface ValidationResult {
   (e.g. `.gitignore` → `''`). Implemented as `lastIndexOf('.') <= 0`.
 - Extension change behavior is controlled by the `allowExtensionChanges` user setting (`yes`/`no`/`ask`). `'ask'`
   returns `ok` at validation time — the save dialog handles it separately.
+- `extensionsDifferIgnoringCase(oldName, newName)` is the shared helper that decides whether an extension change is
+  meaningful. Case-only changes (e.g. `.JPG` → `.jpg`) are treated as no change so users aren't pestered to confirm a
+  metadata tweak. Used by both `validateExtensionChange` and the rename save flow's "ask" gate.
 
 ## confirm-dialog.ts
 

apps/desktop/src/lib/utils/filename-validation.test.ts

@@ -197,6 +197,14 @@ describe('validateExtensionChange', () => {
   it('allows when setting is ask (dialog handles it)', () => {
     expect(validateExtensionChange('file.txt', 'file.md', 'ask').severity).toBe('ok')
   })
+
+  it('allows case-only extension change when setting is no', () => {
+    expect(validateExtensionChange('photo.JPG', 'photo.jpg', 'no').severity).toBe('ok')
+  })
+
+  it('still errors on real extension change when setting is no', () => {
+    expect(validateExtensionChange('file.txt', 'file.md', 'no').severity).toBe('error')
+  })
 })
 
 describe('validateConflict', () => {

apps/desktop/src/lib/utils/filename-validation.ts

@@ -76,6 +76,15 @@ export function getExtension(filename: string): string {
   return filename.substring(lastDot)
 }
 
+/**
+ * True if the extensions differ in more than just letter case.
+ * Case-only extension changes (e.g. `photo.JPG` → `photo.jpg`) are treated as no change,
+ * so users aren't pestered to confirm something that's effectively a metadata tweak.
+ */
+export function extensionsDifferIgnoringCase(oldName: string, newName: string): boolean {
+  return getExtension(oldName).toLowerCase() !== getExtension(newName.trim()).toLowerCase()
+}
+
 /** Validates extension change against the user's preference. */
 export function validateExtensionChange(
   oldName: string,
@@ -84,12 +93,10 @@ export function validateExtensionChange(
 ): ValidationResult {
   if (allowExtensionChanges === 'yes') return OK_RESULT
 
-  const oldExt = getExtension(oldName)
-  const newExt = getExtension(newName.trim())
-
-  if (oldExt === newExt) return OK_RESULT
+  if (!extensionsDifferIgnoringCase(oldName, newName)) return OK_RESULT
 
   if (allowExtensionChanges === 'no') {
+    const oldExt = getExtension(oldName)
     return { severity: 'error', message: `Changing the file extension isn't allowed (was "${oldExt}")` }
   }
   // 'ask' — no error, the dialog will handle it on save