fix(git): lowercase the git-username branch prefix

src/main/ipc/worktree-logic.test.ts

@@ -285,6 +285,15 @@ describe('computeBranchName', () => {
       'jdoe/feature'
     )
   })
+
+  it('omits a git username whose lowercase form git rejects', () => {
+    expect(computeBranchName('feature', { branchPrefix: 'git-username' }, 'Alice.LOCK')).toBe(
+      'feature'
+    )
+    expect(
+      computeValidatedBranchName('feature', { branchPrefix: 'git-username' }, 'Alice.LOCK')
+    ).toBe('feature')
+  })
 })
 
 describe('getConfiguredBranchPrefix', () => {

src/renderer/src/components/settings/BranchPrefixFeedback.tsx

@@ -1,12 +1,20 @@
 import type { ReactNode } from 'react'
-import { getBranchPrefixIssue, normalizeBranchPrefix } from '../../../../shared/branch-prefix'
+import {
+  getBranchPrefixIssue,
+  normalizeBranchPrefix,
+  type GitUsernamePrefixOmission
+} from '../../../../shared/branch-prefix'
 import { translate } from '@/i18n/i18n'
 
 type BranchPrefixFeedbackProps = {
   rawPrefix: string
+  omission?: GitUsernamePrefixOmission | null
 }
 
-export function BranchPrefixFeedback({ rawPrefix }: BranchPrefixFeedbackProps): ReactNode {
+export function BranchPrefixFeedback({
+  rawPrefix,
+  omission = null
+}: BranchPrefixFeedbackProps): ReactNode {
   const issue = getBranchPrefixIssue(rawPrefix)
   const normalized = normalizeBranchPrefix(rawPrefix)
 
@@ -30,6 +38,15 @@ export function BranchPrefixFeedback({ rawPrefix }: BranchPrefixFeedbackProps):
         )}
       </span>
     )
+  } else if (omission === 'lowercase-lock') {
+    message = (
+      <span className="text-muted-foreground">
+        {translate(
+          'auto.components.settings.BranchPrefixFeedback.c478cf4ec7',
+          'No prefix will be applied because lowercasing this username ends in .lock, which Git rejects.'
+        )}
+      </span>
+    )
   } else if (rawPrefix.trim()) {
     message = (
       <span className="text-muted-foreground">

src/renderer/src/components/settings/GitPane.test.tsx

@@ -65,10 +65,26 @@ describe('GitPane branch prefix feedback', () => {
   it('warns in git-username mode when the displayed username is invalid', () => {
     const html = renderGitPane(gitUsernamePrefixSettings(), 'team x')
     expect(html).toContain('Prefix cannot contain spaces')
+    expect(html).not.toContain('which Git rejects')
   })
 
   it('previews in git-username mode when the displayed username is valid', () => {
     const html = renderGitPane(gitUsernamePrefixSettings(), 'jdoe/')
     expect(html).toContain('jdoe/feature')
   })
+
+  it('previews the lowercased git username that new branches use', () => {
+    const html = renderGitPane(gitUsernamePrefixSettings(), 'EurFelux')
+    expect(html).toContain('eurfelux/feature')
+    expect(html).not.toContain('EurFelux')
+  })
+
+  it('does not preview a git username whose lowercase form is not a valid ref', () => {
+    const html = renderGitPane(gitUsernamePrefixSettings(), 'Alice.LOCK')
+    expect(html).toContain(
+      'No prefix will be applied because lowercasing this username ends in .lock, which Git rejects.'
+    )
+    expect(html).not.toContain('Alice.LOCK')
+    expect(html).not.toContain('alice.lock')
+  })
 })

src/renderer/src/components/settings/GitPane.tsx

@@ -9,6 +9,10 @@ import { Switch } from '../ui/switch'
 import { useAppStore } from '../../store'
 import { getGitPaneSearchEntries } from './git-search'
 import { SearchableSetting } from './SearchableSetting'
+import {
+  gitUsernamePrefixOmission,
+  selectBranchPrefixInput
+} from '../../../../shared/branch-prefix'
 import { BranchPrefixFeedback } from './BranchPrefixFeedback'
 import { matchesSettingsSearch } from './settings-search'
 import { AutoRenameBranchFromWorkSetting } from './AutoRenameBranchFromWorkSetting'
@@ -164,7 +168,9 @@ export function GitPane({
     }
   }, [settings.branchPrefixCustom])
   const branchPrefixInputValue =
-    settings.branchPrefix === 'git-username' ? displayedGitUsername : customPrefixDraft
+    settings.branchPrefix === 'git-username'
+      ? (selectBranchPrefixInput(settings, displayedGitUsername || null) ?? '')
+      : customPrefixDraft
 
   const visibleSections = [
     matchesSettingsSearch(searchQuery, {
@@ -228,17 +234,33 @@ export function GitPane({
             }}
             placeholder={
               settings.branchPrefix === 'git-username'
-                ? translate(
-                    'auto.components.settings.GitPane.aefa1ecb59',
-                    'No git username configured'
-                  )
+                ? displayedGitUsername.trim()
+                  ? translate(
+                      'auto.components.settings.BranchPrefixFeedback.808f9a726e',
+                      'No prefix will be applied'
+                    )
+                  : translate(
+                      'auto.components.settings.GitPane.aefa1ecb59',
+                      'No git username configured'
+                    )
                 : translate('auto.components.settings.GitPane.b559bf9899', 'e.g. feature')
             }
             className="max-w-xs"
             readOnly={settings.branchPrefix === 'git-username'}
           />
         )}
-        {isBranchPrefixInputMode && <BranchPrefixFeedback rawPrefix={branchPrefixInputValue} />}
+        {isBranchPrefixInputMode && (
+          <BranchPrefixFeedback
+            rawPrefix={branchPrefixInputValue}
+            omission={
+              settings.branchPrefix === 'git-username'
+                ? gitUsernamePrefixOmission(
+                    displayedGitUsername.trim() ? displayedGitUsername : null
+                  )
+                : null
+            }
+          />
+        )}
       </SearchableSetting>
     ) : null,
     matchesSettingsSearch(searchQuery, {

src/renderer/src/i18n/locales/en.json

@@ -7484,7 +7484,8 @@
         "BranchPrefixFeedback": {
           "6c40c0908f": "Prefix cannot contain spaces or special characters like ~ ^ : ? * [ \\",
           "64d70b156a": "Branches will be named {{example}}",
-          "808f9a726e": "No prefix will be applied"
+          "808f9a726e": "No prefix will be applied",
+          "c478cf4ec7": "No prefix will be applied because lowercasing this username ends in .lock, which Git rejects."
         },
         "GitPane": {
           "895d3f70b8": "gh",

src/renderer/src/i18n/locales/es.json

@@ -6247,7 +6247,8 @@
         "BranchPrefixFeedback": {
           "6c40c0908f": "El prefijo no puede contener espacios ni caracteres especiales como ~ ^ : ? * [ \\",
           "64d70b156a": "Las ramas se llamarán {{example}}",
-          "808f9a726e": "No se aplicará ningún prefijo"
+          "808f9a726e": "No se aplicará ningún prefijo",
+          "c478cf4ec7": "No se aplicará ningún prefijo porque el nombre de usuario en minúsculas termina en .lock y Git lo rechaza."
         },
         "GitPane": {
           "895d3f70b8": "gh",

src/renderer/src/i18n/locales/fr.json

@@ -7417,7 +7417,8 @@
         "BranchPrefixFeedback": {
           "6c40c0908f": "Le préfixe ne peut pas contenir d'espaces ni de caractères spéciaux comme ~ ^ : ? * [ \\",
           "64d70b156a": "Les branches seront nommées {{example}}",
-          "808f9a726e": "Aucun préfixe ne sera appliqué"
+          "808f9a726e": "Aucun préfixe ne sera appliqué",
+          "c478cf4ec7": "Aucun préfixe ne sera appliqué, car le nom d'utilisateur en minuscules se termine par .lock, ce que Git refuse."
         },
         "GitPane": {
           "895d3f70b8": "gh",

src/renderer/src/i18n/locales/ja.json

@@ -7299,7 +7299,8 @@
         "BranchPrefixFeedback": {
           "6c40c0908f": "プレフィックスにスペースや ~ ^ : ? * [ \\ などの特殊文字は使用できません",
           "64d70b156a": "ブランチ名は {{example}} になります",
-          "808f9a726e": "プレフィックスは適用されません"
+          "808f9a726e": "プレフィックスは適用されません",
+          "c478cf4ec7": "このユーザー名を小文字にすると末尾が .lock になり、Git が拒否するため接頭辞は付きません。"
         },
         "GitPane": {
           "895d3f70b8": "gh",

src/renderer/src/i18n/locales/ko.json

@@ -7262,7 +7262,8 @@
         "BranchPrefixFeedback": {
           "6c40c0908f": "접두사에는 공백이나 ~ ^ : ? * [ \\ 같은 특수 문자를 사용할 수 없습니다",
           "64d70b156a": "브랜치 이름은 {{example}}(으)로 지정됩니다",
-          "808f9a726e": "접두사가 적용되지 않습니다"
+          "808f9a726e": "접두사가 적용되지 않습니다",
+          "c478cf4ec7": "이 사용자 이름을 소문자로 바꾸면 .lock으로 끝나 Git이 거절하므로 접두사를 적용하지 않습니다."
         },
         "GitPane": {
           "895d3f70b8": "gh",

src/renderer/src/i18n/locales/zh.json

@@ -7262,7 +7262,8 @@
         "BranchPrefixFeedback": {
           "6c40c0908f": "前缀不能包含空格或 ~ ^ : ? * [ \\ 等特殊字符",
           "64d70b156a": "分支将命名为 {{example}}",
-          "808f9a726e": "不会应用前缀"
+          "808f9a726e": "不会应用前缀",
+          "c478cf4ec7": "将此用户名转为小写后会以 .lock 结尾，Git 会拒绝，因此不会应用前缀。"
         },
         "GitPane": {
           "895d3f70b8": "gh",

src/shared/branch-prefix.test.ts

@@ -2,6 +2,7 @@ import { describe, expect, it } from 'vitest'
 import {
   assertBranchPrefixValid,
   getBranchPrefixIssue,
+  gitUsernamePrefixOmission,
   normalizeBranchPrefix,
   selectBranchPrefixInput
 } from './branch-prefix'
@@ -113,6 +114,33 @@ describe('selectBranchPrefixInput', () => {
     expect(selectBranchPrefixInput({ branchPrefix: 'git-username' }, 'jdoe')).toBe('jdoe')
   })
 
+  it('lowercases a git-username prefix so it cannot collide with an existing ref directory', () => {
+    expect(selectBranchPrefixInput({ branchPrefix: 'git-username' }, 'EurFelux')).toBe('eurfelux')
+  })
+
+  it('drops a mixed-case login whose lowercase form git rejects', () => {
+    expect(selectBranchPrefixInput({ branchPrefix: 'git-username' }, 'Alice.LOCK')).toBeNull()
+    expect(gitUsernamePrefixOmission('Alice.LOCK')).toBe('lowercase-lock')
+    expect(gitUsernamePrefixOmission('alice.lock')).toBeNull()
+    expect(gitUsernamePrefixOmission('team x')).toBeNull()
+    expect(gitUsernamePrefixOmission('EurFelux')).toBeNull()
+    expect(gitUsernamePrefixOmission(null)).toBeNull()
+  })
+
+  it('returns an already-lowercase invalid login so settings can warn', () => {
+    expect(selectBranchPrefixInput({ branchPrefix: 'git-username' }, 'alice.lock')).toBe('alice.lock')
+    expect(selectBranchPrefixInput({ branchPrefix: 'git-username' }, 'team x')).toBe('team x')
+  })
+
+  it('leaves a custom prefix in the case the user typed', () => {
+    expect(
+      selectBranchPrefixInput(
+        { branchPrefix: 'custom', branchPrefixCustom: 'EurFelux' },
+        'eurfelux'
+      )
+    ).toBe('EurFelux')
+  })
+
   it('returns null for git-username when no username is available', () => {
     expect(selectBranchPrefixInput({ branchPrefix: 'git-username' }, null)).toBeNull()
   })

src/shared/branch-prefix.ts

@@ -6,18 +6,64 @@ export type BranchPrefixSettings = {
   branchPrefixCustom?: string
 }
 
+/** A configured login was not used because its lowercase form is a rejected ref. */
+export type GitUsernamePrefixOmission = 'lowercase-lock'
+
 /**
- * Pick the raw, un-normalized value the configured strategy contributes, or
- * null when no prefix applies. Shared so the main-process branch builder and
- * the renderer's live settings feedback agree on which field each strategy uses.
+ * Why Settings omits a git username. Only a mixed-case login whose lowercase
+ * form git rejects (`.LOCK` → `.lock`) is omitted. An already-lowercase invalid
+ * login stays visible so the existing character warning still explains it.
+ */
+export function gitUsernamePrefixOmission(
+  gitUsername: string | null
+): GitUsernamePrefixOmission | null {
+  if (gitUsername === null) {
+    return null
+  }
+  const lower = gitUsername.toLowerCase()
+  if (lower === gitUsername || getBranchPrefixIssue(lower) === null) {
+    return null
+  }
+  if (getBranchPrefixIssue(gitUsername) !== null) {
+    return null
+  }
+  return 'lowercase-lock'
+}
+
+/**
+ * Pick the value the configured strategy contributes, or null when no prefix
+ * applies. Shared so the main-process branch builder and the renderer's live
+ * settings feedback agree on which field each strategy uses.
+ *
+ * A git username is lowercased so a mixed-case login cannot collide with an
+ * existing lowercase ref directory on a case-insensitive filesystem. When that
+ * lowercase form is a ref git rejects (`Alice.LOCK` becomes `alice.lock`), drop
+ * the prefix. Keeping the original login creates `refs/heads/Alice.LOCK/`, which
+ * occupies the `alice.lock` lockfile path on a case-insensitive filesystem.
  */
 export function selectBranchPrefixInput(
   settings: BranchPrefixSettings,
   gitUsername: string | null
 ): string | null {
   switch (settings.branchPrefix) {
-    case 'git-username':
-      return gitUsername
+    case 'git-username': {
+      if (gitUsername === null) {
+        return null
+      }
+      const lower = gitUsername.toLowerCase()
+      if (getBranchPrefixIssue(lower) === null) {
+        return lower
+      }
+      // The original can pass git's case-sensitive check while its lowercase
+      // form is `*.lock`. Keeping that original still collides on a
+      // case-insensitive filesystem, so the prefix is omitted. An
+      // already-lowercase invalid login is returned unchanged so settings can
+      // show the rejection instead of pretending no username was configured.
+      if (gitUsernamePrefixOmission(gitUsername) === 'lowercase-lock') {
+        return null
+      }
+      return lower
+    }
     case 'custom':
       return settings.branchPrefixCustom ?? null
     case 'none':