fix(desktop): clarify branch convert actions

Open checked-out branches, switch the primary checkout for the default branch, and create linked worktrees only for non-trunk free branches.

apps/desktop/electron/git-worktree-ops.cjs

@@ -111,6 +111,41 @@ function slugify(name) {
   return slug || 'work'
 }
 
+const TRUNK_BRANCHES = ['main', 'master']
+
+async function gitLine(gitBin, args, cwd) {
+  try {
+    return (await runGit(gitBin, args, cwd)).trim()
+  } catch {
+    return ''
+  }
+}
+
+async function defaultBranch(gitBin, cwd) {
+  const remote = (await gitLine(gitBin, ['symbolic-ref', '--quiet', '--short', 'refs/remotes/origin/HEAD'], cwd)).replace(
+    /^origin\//,
+    ''
+  )
+
+  if (remote) {
+    return remote
+  }
+
+  const configured = await gitLine(gitBin, ['config', '--get', 'init.defaultBranch'], cwd)
+
+  if (configured) {
+    return configured
+  }
+
+  for (const branch of TRUNK_BRANCHES) {
+    if (await gitLine(gitBin, ['show-ref', '--verify', `refs/heads/${branch}`], cwd)) {
+      return branch
+    }
+  }
+
+  return ''
+}
+
 // A brand-new project folder isn't a git repo — and a freshly-init'd one has no
 // commit to branch from — so `git worktree add` would fail. Make the dir a repo
 // with a root commit on the user's behalf so worktrees "just work". No-op for a
@@ -169,6 +204,25 @@ function uniqueDir(base) {
   return dir
 }
 
+async function addExistingBranchWorktree(gitBin, root, name) {
+  const branch = sanitizeBranch(name)
+
+  if (!branch) {
+    throw new Error('Branch name is required.')
+  }
+
+  if (branch === (await defaultBranch(gitBin, root))) {
+    await runGit(gitBin, ['switch', branch], root)
+
+    return { path: root, branch, repoRoot: root }
+  }
+
+  const dir = uniqueDir(path.join(root, '.worktrees', slugify(branch)))
+  await runGit(gitBin, ['worktree', 'add', dir, branch], root)
+
+  return { path: dir, branch, repoRoot: root }
+}
+
 async function addWorktree(repoPath, options, gitBin) {
   const resolved = resolveRequestedPathForIpc(repoPath, { purpose: 'Worktree add' })
   // A new project's folder may not be a git repo yet — init it (with a root
@@ -177,20 +231,8 @@ async function addWorktree(repoPath, options, gitBin) {
   const root = await mainRoot(gitBin, resolved)
   const opts = options || {}
 
-  // "Convert an existing branch into a worktree": check the branch out into a
-  // fresh worktree dir as-is (no `-b`, no new branch). Dir is named off the
-  // branch slug so it reads like the branch it carries.
   if (opts.existingBranch) {
-    const existing = sanitizeBranch(opts.existingBranch)
-
-    if (!existing) {
-      throw new Error('Branch name is required.')
-    }
-
-    const dir = uniqueDir(path.join(root, '.worktrees', slugify(existing)))
-    await runGit(gitBin, ['worktree', 'add', dir, existing], root)
-
-    return { path: dir, branch: existing, repoRoot: root }
+    return addExistingBranchWorktree(gitBin, root, opts.existingBranch)
   }
 
   const slug = slugify(opts.name || `work-${Date.now().toString(36)}`)
@@ -255,12 +297,18 @@ async function listBranches(repoPath, gitBin) {
     )
     const trees = await listWorktrees(resolved, gitBin)
     const pathByBranch = new Map(trees.filter(tree => tree.branch).map(tree => [tree.branch, tree.path]))
+    const trunk = await defaultBranch(gitBin, resolved)
 
     return out
       .split('\n')
       .map(line => line.trim())
       .filter(Boolean)
-      .map(name => ({ name, checkedOut: pathByBranch.has(name), worktreePath: pathByBranch.get(name) || null }))
+      .map(name => ({
+        name,
+        checkedOut: pathByBranch.has(name),
+        isDefault: Boolean(trunk && name === trunk),
+        worktreePath: pathByBranch.get(name) || null
+      }))
   } catch {
     return []
   }

apps/desktop/electron/git-worktree-ops.test.cjs

@@ -108,14 +108,36 @@ test('listBranches: lists locals and flags the checked-out branch', async () =>
     assert.deepEqual(names, [current, 'feature'].sort())
     // The repo's own checkout is flagged; the unused branch is convertible.
     assert.equal(branches.find(b => b.name === current).checkedOut, true)
+    assert.equal(branches.find(b => b.name === current).isDefault, true)
     assert.equal(fs.realpathSync(branches.find(b => b.name === current).worktreePath), fs.realpathSync(dir))
     assert.equal(branches.find(b => b.name === 'feature').checkedOut, false)
+    assert.equal(branches.find(b => b.name === 'feature').isDefault, false)
     assert.equal(branches.find(b => b.name === 'feature').worktreePath, null)
   } finally {
     fs.rmSync(dir, { recursive: true, force: true })
   }
 })
 
+test('listBranches: flags a free default branch as default, not checked out', async () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-branches-default-'))
+  const git = (...args) => execFileSync('git', args, { cwd: dir }).toString().trim()
+
+  try {
+    await ensureGitRepo('git', dir)
+    const trunk = git('branch', '--show-current')
+    execFileSync('git', ['switch', '-c', 'rawr'], { cwd: dir })
+
+    const branches = await listBranches(dir, 'git')
+    const defaultBranch = branches.find(b => b.name === trunk)
+
+    assert.equal(defaultBranch.checkedOut, false)
+    assert.equal(defaultBranch.isDefault, true)
+    assert.equal(defaultBranch.worktreePath, null)
+  } finally {
+    fs.rmSync(dir, { recursive: true, force: true })
+  }
+})
+
 test('listBranches: a branch claimed by a worktree is flagged checked out', async () => {
   const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-branches-wt-'))
 
@@ -170,3 +192,23 @@ test('addWorktree: existingBranch checks the branch out without a new branch', a
     fs.rmSync(dir, { recursive: true, force: true })
   }
 })
+
+test('addWorktree: existing default branch switches the main checkout, not .worktrees/main', async () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-convert-default-'))
+  const git = (...args) => execFileSync('git', args, { cwd: dir }).toString().trim()
+
+  try {
+    await ensureGitRepo('git', dir)
+    const trunk = git('branch', '--show-current')
+    execFileSync('git', ['switch', '-c', 'rawr'], { cwd: dir })
+
+    const result = await addWorktree(dir, { existingBranch: trunk }, 'git')
+
+    assert.equal(result.branch, trunk)
+    assert.equal(fs.realpathSync(result.path), fs.realpathSync(dir))
+    assert.equal(git('branch', '--show-current'), trunk)
+    assert.equal(fs.existsSync(path.join(dir, '.worktrees', trunk)), false)
+  } finally {
+    fs.rmSync(dir, { recursive: true, force: true })
+  }
+})

apps/desktop/src/app/chat/composer/index.tsx

@@ -1387,7 +1387,7 @@ export function ChatBar({
   // Mirrors handleBranchOff's hand-off: create the worktree, then open a session
   // anchored there carrying the draft.
   const handleConvertBranch = useCallback(
-    async (branch: string, path?: null | string) => {
+    async (branch: string, path?: null | string, isDefault?: boolean) => {
       if (path?.trim()) {
         openInWorktree(path)
 
@@ -1395,6 +1395,14 @@ export function ChatBar({
       }
 
       const repoPath = cwd?.trim()
+
+      if (repoPath && isDefault) {
+        await switchBranchInRepo(repoPath, branch)
+        openInWorktree(repoPath)
+
+        return
+      }
+
       const result = repoPath && (await startWorkInRepo(repoPath, { existingBranch: branch }))
 
       if (result) {

apps/desktop/src/app/chat/composer/status-stack/coding-row.tsx

@@ -40,6 +40,20 @@ import { $newWorktreeRequest } from '@/store/projects'
 // Tiny uppercase section header, matching the composer "+" menu's labels.
 const MENU_SECTION = 'text-[0.625rem] font-semibold uppercase tracking-wider text-(--ui-text-tertiary)'
 
+interface BranchActionCopy {
+  branchCreateWorktree: string
+  branchOpenExisting: string
+  branchSwitchHome: string
+}
+
+const branchActionLabel = (branch: HermesGitBranch, copy: BranchActionCopy) => {
+  if (branch.checkedOut) {
+    return copy.branchOpenExisting
+  }
+
+  return branch.isDefault ? copy.branchSwitchHome : copy.branchCreateWorktree
+}
+
 interface CodingStatusRowProps {
   /** Branch the current draft off into a fresh worktree + session, based on
    *  `base` (a branch name; omitted = current HEAD). The composer owns the
@@ -48,7 +62,7 @@ interface CodingStatusRowProps {
   onBranchOff?: (branch: string, base?: string) => Promise<void>
   /** Check an existing branch out into a fresh worktree + session (no new
    *  branch). Drives the dialog's "convert a branch" picker. */
-  onConvertBranch?: (branch: string, path?: null | string) => Promise<void>
+  onConvertBranch?: (branch: string, path?: null | string, isDefault?: boolean) => Promise<void>
   /** List the repo's local branches for the "convert a branch" picker. */
   onListBranches?: () => Promise<HermesGitBranch[]>
   /** Open the review pane (changed files + diffs). */
@@ -84,15 +98,10 @@ export const CodingStatusRow = memo(function CodingStatusRow({
   const [branchName, setBranchName] = useState('')
   const [branchBase, setBranchBase] = useState<string | undefined>(undefined)
   const [branchPending, setBranchPending] = useState(false)
-  // "Convert an existing branch into a worktree" sub-mode of the dialog: the body
-  // swaps the new-branch name input for a filterable list of the repo's branches.
   const [convertMode, setConvertMode] = useState(false)
   const [branches, setBranches] = useState<HermesGitBranch[]>([])
   const [branchesLoading, setBranchesLoading] = useState(false)
 
-  // Pull the repo's branches the first time the convert picker is shown for an
-  // open dialog. Cheap + bounded; refreshed each time the picker is entered so a
-  // branch created mid-session shows up.
   const loadBranches = useCallback(async () => {
     if (!onListBranches) {
       return
@@ -119,7 +128,6 @@ export const CodingStatusRow = memo(function CodingStatusRow({
     setTimeout(() => setBranchOpen(true), 0)
   }
 
-  // Open the dialog straight into the convert-a-branch picker.
   const startConvert = () => {
     setBranchBase(undefined)
     setBranchName('')
@@ -128,7 +136,6 @@ export const CodingStatusRow = memo(function CodingStatusRow({
     setTimeout(() => setBranchOpen(true), 0)
   }
 
-  // Flip an already-open dialog into the picker (the in-dialog link).
   const enterConvert = () => {
     setConvertMode(true)
     void loadBranches()
@@ -142,7 +149,7 @@ export const CodingStatusRow = memo(function CodingStatusRow({
     setBranchPending(true)
 
     try {
-      await onConvertBranch(branch.name, branch.worktreePath)
+      await onConvertBranch(branch.name, branch.worktreePath, branch.isDefault)
       setBranchOpen(false)
     } catch (err) {
       notifyError(err, p.startWorkFailed)
@@ -393,11 +400,9 @@ export const CodingStatusRow = memo(function CodingStatusRow({
                     >
                       <Codicon className="shrink-0 text-(--ui-text-tertiary)" name="git-branch" size="0.8rem" />
                       <span className="truncate">{branch.name}</span>
-                      {branch.checkedOut && (
-                        <span className="ml-auto shrink-0 text-[0.625rem] text-(--ui-text-tertiary)">
-                          {p.branchCheckedOut}
-                        </span>
-                      )}
+                      <span className="ml-auto shrink-0 text-[0.625rem] text-(--ui-text-tertiary)">
+                        {branchActionLabel(branch, p)}
+                      </span>
                     </CommandItem>
                   ))}
                 </CommandGroup>
@@ -423,8 +428,6 @@ export const CodingStatusRow = memo(function CodingStatusRow({
           )}
 
           {convertMode ? (
-            // The picker is a sub-screen: a single "Cancel" link steps back to
-            // the new-branch screen (the dialog's own ✕ / Esc still closes it).
             <DialogFooter className="sm:justify-start">
               <Button
                 className="px-0 text-(--ui-text-secondary) hover:text-foreground"
@@ -438,7 +441,6 @@ export const CodingStatusRow = memo(function CodingStatusRow({
             </DialogFooter>
           ) : (
             <DialogFooter className="sm:justify-between">
-              {/* Switch into the convert-an-existing-branch picker. */}
               {onConvertBranch ? (
                 <Button
                   className="px-0 text-(--ui-text-secondary) hover:text-foreground"

apps/desktop/src/app/chat/right-rail/preview-file.tsx

@@ -6,7 +6,7 @@ import type {
   MouseEvent as ReactMouseEvent,
   ReactNode
 } from 'react'
-import { useEffect, useMemo, useState } from 'react'
+import { Fragment, useEffect, useMemo, useState } from 'react'
 import ShikiHighlighter from 'react-shiki'
 import { Streamdown } from 'streamdown'
 
@@ -14,15 +14,21 @@ import { requestComposerFocus, requestComposerInsertRefs } from '@/app/chat/comp
 import { droppedFileInlineRef } from '@/app/chat/composer/inline-refs'
 import { HERMES_PATHS_MIME } from '@/app/chat/hooks/use-composer-actions'
 import { isAddSelectionShortcut } from '@/app/right-sidebar/terminal/selection'
+import { FileDiffPanel } from '@/components/chat/diff-lines'
+import { chunkTextLines, useFixedRowWindow } from '@/components/chat/fixed-row-window'
 import { PageLoader } from '@/components/page-loader'
 import { translateNow, useI18n } from '@/i18n'
-import { readDesktopFileDataUrl, readDesktopFileText } from '@/lib/desktop-fs'
+import { desktopFileDiff, desktopGitRoot, readDesktopFileDataUrl, readDesktopFileText } from '@/lib/desktop-fs'
+import { shikiLanguageForFilename } from '@/lib/markdown-code'
 import { cn } from '@/lib/utils'
 import type { PreviewTarget } from '@/store/preview'
 import { $currentCwd } from '@/store/session'
 
 const SHIKI_THEME = { dark: 'github-dark-default', light: 'github-light-default' } as const
 const TEXT_PREVIEW_MAX_BYTES = 512 * 1024
+const SOURCE_CHUNK_LINES = 200
+const SOURCE_LINE_PX = 20
+const SOURCE_OVERSCAN_LINES = 400
 
 type EmptyStateTone = 'neutral' | 'warning'
 
@@ -126,6 +132,8 @@ interface LocalPreviewState {
   binary?: boolean
   byteSize?: number
   dataUrl?: string
+  /** Working-tree-vs-HEAD unified diff, when the file has uncommitted changes. */
+  diff?: string
   error?: string
   language?: string
   loading: boolean
@@ -299,28 +307,44 @@ function MarkdownPreview({ text }: { text: string }) {
   )
 }
 
-function PreviewToggle({ asSource, onToggle }: { asSource: boolean; onToggle: () => void }) {
+function PreviewModeSwitcher({
+  active,
+  modes,
+  onSelect
+}: {
+  active: PreviewViewMode
+  modes: PreviewViewMode[]
+  onSelect: (mode: PreviewViewMode) => void
+}) {
   const { t } = useI18n()
 
+  const label: Record<PreviewViewMode, string> = {
+    diff: t.preview.diff,
+    rendered: t.preview.renderedPreview,
+    source: t.preview.source
+  }
+
   return (
-    <div className="sticky top-0 z-10 flex justify-end border-b border-border/40 bg-transparent px-3 py-1 backdrop-blur">
-      <button
-        className="text-[0.625rem] font-bold text-muted-foreground underline decoration-current/20 underline-offset-4 transition-colors hover:text-foreground"
-        onClick={onToggle}
-        type="button"
-      >
-        {asSource ? t.preview.renderedPreview : t.preview.source}
-      </button>
+    <div className="flex shrink-0 justify-end gap-3 border-b border-border/40 px-3 py-1">
+      {modes.map(mode => (
+        <button
+          className={cn(
+            'text-[0.625rem] font-bold underline-offset-4 transition-colors',
+            mode === active
+              ? 'text-foreground underline decoration-current/30'
+              : 'text-muted-foreground hover:text-foreground'
+          )}
+          key={mode}
+          onClick={() => onSelect(mode)}
+          type="button"
+        >
+          {label[mode]}
+        </button>
+      ))}
     </div>
   )
 }
 
-// Gutter and Shiki output share `font-mono text-xs leading-relaxed py-3` so
-// each line aligns vertically. The selection overlay relies on the same
-// `text-xs * leading-relaxed = 1.21875rem` line-height to position itself.
-const SOURCE_LINE_HEIGHT_REM = 1.21875
-const SOURCE_PAD_Y_REM = 0.75
-
 interface LineSelection {
   end: number
   start: number
@@ -337,7 +361,18 @@ function startLineDrag(event: ReactDragEvent<HTMLElement>, filePath: string, { e
 
 function SourceView({ filePath, language, text }: { filePath: string; language: string; text: string }) {
   const { t } = useI18n()
-  const lineCount = useMemo(() => Math.max(1, text.split('\n').length), [text])
+  const chunks = useMemo(() => chunkTextLines(text, SOURCE_CHUNK_LINES), [text])
+  const lastChunk = chunks.at(-1)
+  const totalLines = lastChunk ? lastChunk.start + lastChunk.lines.length : 0
+
+  const { afterRows, beforeRows, endChunk, onScroll, scrollerRef, startChunk } = useFixedRowWindow({
+    overscanRows: SOURCE_OVERSCAN_LINES,
+    rowPx: SOURCE_LINE_PX,
+    rowsPerChunk: SOURCE_CHUNK_LINES,
+    totalRows: totalLines
+  })
+
+  const visibleChunks = chunks.slice(startChunk, endChunk + 1)
   const [selection, setSelection] = useState<LineSelection | null>(null)
   const inSelection = (line: number) => selection != null && line >= selection.start && line <= selection.end
 
@@ -394,69 +429,76 @@ function SourceView({ filePath, language, text }: { filePath: string; language:
   }, [filePath, selection])
 
   return (
-    <div className="grid min-w-max grid-cols-[auto_minmax(0,1fr)] font-mono text-xs leading-relaxed">
-      <div className="select-none py-3 text-right text-muted-foreground/55">
-        {Array.from({ length: lineCount }, (_, index) => {
-          const line = index + 1
-          const selected = inSelection(line)
-
-          return (
-            <div
-              className={cn(
-                'cursor-pointer px-3 tabular-nums transition-colors',
-                selected
-                  ? 'bg-amber-200/45 text-amber-900 dark:bg-amber-300/20 dark:text-amber-100'
-                  : 'hover:text-foreground'
-              )}
-              draggable
-              key={line}
-              onClick={event => handleLineClick(event, line)}
-              onDragStart={event => handleDragStart(event, line)}
-              title={t.preview.sourceLineTitle}
-            >
-              {line}
-            </div>
-          )
-        })}
-      </div>
-      <div
-        className="relative [&_pre]:m-0 [&_pre]:px-3 [&_pre]:py-3 [&_pre]:bg-transparent!"
-        data-selectable-text="true"
-      >
-        {selection && (
-          <div
-            aria-hidden
-            className="pointer-events-none absolute inset-x-0 bg-amber-200/35 dark:bg-amber-300/10"
-            style={{
-              top: `calc(${SOURCE_PAD_Y_REM}rem + ${selection.start - 1} * ${SOURCE_LINE_HEIGHT_REM}rem)`,
-              height: `calc(${selection.end - selection.start + 1} * ${SOURCE_LINE_HEIGHT_REM}rem)`
-            }}
-          />
+    <div className="h-full overflow-auto" onScroll={onScroll} ref={scrollerRef}>
+      <div className="grid min-w-max grid-cols-[auto_minmax(0,1fr)] font-mono text-[0.7rem] leading-relaxed">
+        {beforeRows > 0 && (
+          <div aria-hidden className="col-span-2" style={{ height: beforeRows * SOURCE_LINE_PX }} />
+        )}
+        {visibleChunks.map(chunk => (
+          <Fragment key={chunk.start}>
+            <div className="select-none text-right text-muted-foreground/55">
+              {chunk.lines.map((_lineText, offset) => {
+                const line = chunk.start + offset + 1
+                const selected = inSelection(line)
+
+                return (
+                  <div
+                    className={cn(
+                      'h-5 w-9 cursor-pointer pr-2 leading-5 tabular-nums transition-colors',
+                      selected
+                        ? 'bg-amber-200/45 text-amber-900 dark:bg-amber-300/20 dark:text-amber-100'
+                        : 'hover:text-foreground'
+                    )}
+                    draggable
+                    key={line}
+                    onClick={event => handleLineClick(event, line)}
+                    onDragStart={event => handleDragStart(event, line)}
+                    title={t.preview.sourceLineTitle}
+                  >
+                    {line}
+                  </div>
+                )
+              })}
+            </div>
+            <div className="preview-source-code min-w-0 [&_pre]:m-0" data-selectable-text="true">
+              <ShikiHighlighter
+                addDefaultStyles={false}
+                as="div"
+                defaultColor="light-dark()"
+                delay={80}
+                language={language || 'text'}
+                showLanguage={false}
+                theme={SHIKI_THEME}
+              >
+                {chunk.text}
+              </ShikiHighlighter>
+            </div>
+          </Fragment>
+        ))}
+        {afterRows > 0 && (
+          <div aria-hidden className="col-span-2" style={{ height: afterRows * SOURCE_LINE_PX }} />
         )}
-        <ShikiHighlighter
-          addDefaultStyles={false}
-          as="div"
-          defaultColor="light-dark()"
-          delay={80}
-          language={language || 'text'}
-          showLanguage={false}
-          theme={SHIKI_THEME}
-        >
-          {text}
-        </ShikiHighlighter>
       </div>
     </div>
   )
 }
 
+type PreviewViewMode = 'diff' | 'rendered' | 'source'
+
 export function LocalFilePreview({ reloadKey, target }: { reloadKey: number; target: PreviewTarget }) {
   const { t } = useI18n()
   const [state, setState] = useState<LocalPreviewState>({ loading: true })
   const [forcePreview, setForcePreview] = useState(false)
-  const [renderMarkdownAsSource, setRenderMarkdownAsSource] = useState(false)
+  // User-picked view; null = auto (diff when changed, else rendered markdown,
+  // else source). Reset when the previewed file changes.
+  const [userMode, setUserMode] = useState<null | PreviewViewMode>(null)
   const filePath = filePathForTarget(target)
   const isImage = target.previewKind === 'image'
 
+  useEffect(() => {
+    setUserMode(null)
+  }, [filePath, reloadKey])
+
   // HTML files are rendered as source code, not in a webview - so they take
   // the same path as plain text files. `previewKind === 'binary'` arrives
   // when the file is forcibly previewed past the binary refusal screen.
@@ -508,6 +550,22 @@ export function LocalFilePreview({ reloadKey, target }: { reloadKey: number; tar
             text: shouldBlock ? undefined : result.text,
             truncated: result.truncated
           })
+
+          // Best-effort: fetch the file's working-tree-vs-HEAD diff so the
+          // preview can offer a DIFF view when there are uncommitted changes.
+          // Empty (clean file / not a repo / remote) just hides the option.
+          if (!shouldBlock) {
+            try {
+              const root = await desktopGitRoot(filePath)
+              const diff = root ? await desktopFileDiff(root, filePath) : ''
+
+              if (active && diff.trim()) {
+                setState(prev => (prev.text === result.text ? { ...prev, diff } : prev))
+              }
+            } catch {
+              // No diff available; the preview just shows source.
+            }
+          }
         }
       } catch (error) {
         if (active) {
@@ -571,21 +629,50 @@ export function LocalFilePreview({ reloadKey, target }: { reloadKey: number; tar
 
   if (isText && state.text !== undefined) {
     const isMarkdown = (state.language || target.language) === 'markdown'
-    const showRendered = isMarkdown && !renderMarkdownAsSource
+    const hasDiff = Boolean(state.diff && state.diff.trim())
+    // Order the toggle reads left→right; default lands on the most useful view.
+    const modes: PreviewViewMode[] = []
+
+    if (isMarkdown) {
+      modes.push('rendered')
+    }
+
+    modes.push('source')
+
+    if (hasDiff) {
+      modes.push('diff')
+    }
+
+    const autoMode: PreviewViewMode = hasDiff ? 'diff' : isMarkdown ? 'rendered' : 'source'
+    const mode = userMode && modes.includes(userMode) ? userMode : autoMode
 
     return (
-      <div className="h-full overflow-auto bg-transparent">
+      <div className="flex h-full flex-col overflow-hidden bg-transparent">
         {state.truncated && (
           <div className="border-b border-border/60 bg-muted/35 px-3 py-1.5 text-[0.68rem] text-muted-foreground">
             {t.preview.truncated}
           </div>
         )}
-        {isMarkdown && <PreviewToggle asSource={!showRendered} onToggle={() => setRenderMarkdownAsSource(s => !s)} />}
-        {showRendered ? (
-          <MarkdownPreview text={state.text} />
-        ) : (
-          <SourceView filePath={filePath} language={state.language || 'text'} text={state.text} />
-        )}
+        {modes.length > 1 && <PreviewModeSwitcher active={mode} modes={modes} onSelect={setUserMode} />}
+        <div className="min-h-0 flex-1 overflow-auto">
+          {mode === 'rendered' ? (
+            <MarkdownPreview text={state.text} />
+          ) : mode === 'diff' ? (
+            <FileDiffPanel
+              className="mx-0 mb-0 h-full max-h-none"
+              diff={state.diff ?? ''}
+              fullText={state.text}
+              path={filePath}
+              showLineNumbers
+            />
+          ) : (
+            <SourceView
+              filePath={filePath}
+              language={shikiLanguageForFilename(filePath) || state.language || 'text'}
+              text={state.text}
+            />
+          )}
+        </div>
       </div>
     )
   }

apps/desktop/src/app/chat/right-rail/preview.tsx

@@ -3,10 +3,19 @@ import { useEffect, useMemo } from 'react'
 
 import type { SetTitlebarToolGroup } from '@/app/shell/titlebar-controls'
 import { Codicon } from '@/components/ui/codicon'
+import {
+  ContextMenu,
+  ContextMenuContent,
+  ContextMenuItem,
+  ContextMenuSeparator,
+  ContextMenuTrigger
+} from '@/components/ui/context-menu'
 import { Tip } from '@/components/ui/tooltip'
 import { translateNow, useI18n } from '@/i18n'
+import { formatCombo } from '@/lib/keybinds/combo'
 import { cn } from '@/lib/utils'
 import {
+  $panesFlipped,
   $rightRailActiveTabId,
   RIGHT_RAIL_PREVIEW_TAB_ID,
   type RightRailTabId,
@@ -16,8 +25,10 @@ import {
   $filePreviewTabs,
   $previewReloadRequest,
   $previewTarget,
+  closeOtherRightRailTabs,
   closeRightRail,
   closeRightRailTab,
+  closeRightRailTabsToRight,
   type PreviewTarget
 } from '@/store/preview'
 
@@ -56,6 +67,7 @@ export function ChatPreviewRail({ onRestartServer, setTitlebarToolGroup }: ChatP
   const { t } = useI18n()
   const previewReloadRequest = useStore($previewReloadRequest)
   const activeTabId = useStore($rightRailActiveTabId)
+  const panesFlipped = useStore($panesFlipped)
   const filePreviewTabs = useStore($filePreviewTabs)
   const previewTarget = useStore($previewTarget)
 
@@ -82,68 +94,92 @@ export function ChatPreviewRail({ onRestartServer, setTitlebarToolGroup }: ChatP
   const isPreview = activeTab.id === RIGHT_RAIL_PREVIEW_TAB_ID
 
   return (
-    <aside className="relative flex h-full w-full min-w-0 flex-col overflow-hidden border-l border-(--ui-stroke-tertiary) bg-(--ui-editor-surface-background) text-(--ui-text-tertiary)">
+    <aside
+      className={cn(
+        'relative flex h-full w-full min-w-0 flex-col overflow-hidden border-(--ui-stroke-tertiary) bg-(--ui-editor-surface-background) text-(--ui-text-tertiary)',
+        panesFlipped ? 'border-r' : 'border-l'
+      )}
+    >
       <div className="group/rail-tabs flex h-(--titlebar-height) shrink-0 border-b border-(--ui-stroke-tertiary) bg-(--ui-sidebar-surface-background)">
         <div
           className="flex min-w-0 flex-1 overflow-x-auto overflow-y-hidden overscroll-x-contain [-ms-overflow-style:none] [scrollbar-width:none] [&::-webkit-scrollbar]:hidden"
           role="tablist"
         >
-          {tabs.map(tab => {
+          {tabs.map((tab, index) => {
             const active = tab.id === activeTab.id
+            const hasOthers = tabs.length > 1
+            const hasTabsToRight = index < tabs.length - 1
 
             return (
-              <div
-                className={cn(
-                  'group/tab relative flex h-full min-w-0 max-w-48 shrink-0 items-center text-[0.6875rem] font-medium [-webkit-app-region:no-drag] last:border-r last:border-(--ui-stroke-quaternary)',
-                  active
-                    ? 'bg-(--ui-editor-surface-background) text-foreground [--tab-bg:var(--ui-editor-surface-background)]'
-                    : 'border-r border-(--ui-stroke-quaternary) text-(--ui-text-tertiary) [--tab-bg:var(--ui-sidebar-surface-background)] hover:bg-(--chrome-action-hover) hover:text-foreground'
-                )}
-                key={tab.id}
-                // Middle-click closes the tab, matching browser/IDE muscle
-                // memory. `onMouseDown` swallows the middle-button press so
-                // Chromium doesn't switch into autoscroll mode.
-                onAuxClick={event => {
-                  if (event.button !== 1) {
-                    return
-                  }
+              <ContextMenu key={tab.id}>
+                <ContextMenuTrigger asChild>
+                  <div
+                    className={cn(
+                      'group/tab relative flex h-full min-w-0 max-w-48 shrink-0 items-center text-[0.6875rem] font-medium [-webkit-app-region:no-drag] last:border-r last:border-(--ui-stroke-quaternary)',
+                      active
+                        ? 'bg-(--ui-editor-surface-background) text-foreground [--tab-bg:var(--ui-editor-surface-background)]'
+                        : 'border-r border-(--ui-stroke-quaternary) text-(--ui-text-tertiary) [--tab-bg:var(--ui-sidebar-surface-background)] hover:bg-(--chrome-action-hover) hover:text-foreground'
+                    )}
+                    // Middle-click closes the tab, matching browser/IDE muscle
+                    // memory. `onMouseDown` swallows the middle-button press so
+                    // Chromium doesn't switch into autoscroll mode.
+                    onAuxClick={event => {
+                      if (event.button !== 1) {
+                        return
+                      }
 
-                  event.preventDefault()
-                  closeRightRailTab(tab.id)
-                }}
-                onMouseDown={event => {
-                  if (event.button === 1) {
-                    event.preventDefault()
-                  }
-                }}
-              >
-                {active && (
-                  <span aria-hidden="true" className="absolute inset-x-0 top-0 h-px bg-(--ui-stroke-primary)" />
-                )}
-                <Tip label={tab.label}>
-                  <button
-                    aria-selected={active}
-                    className="flex h-full min-w-0 max-w-full items-center overflow-hidden pl-3 pr-2 text-left outline-none"
-                    onClick={() => selectRightRailTab(tab.id)}
-                    role="tab"
-                    type="button"
+                      event.preventDefault()
+                      closeRightRailTab(tab.id)
+                    }}
+                    onMouseDown={event => {
+                      if (event.button === 1) {
+                        event.preventDefault()
+                      }
+                    }}
                   >
-                    <span className="block min-w-0 truncate">{tab.label}</span>
-                  </button>
-                </Tip>
-                <span
-                  aria-hidden="true"
-                  className="pointer-events-none absolute inset-y-0 right-0 w-9 bg-[linear-gradient(to_right,transparent,var(--tab-bg)_55%)] opacity-0 transition-opacity group-hover/tab:opacity-100 group-focus-within/tab:opacity-100"
-                />
-                <button
-                  aria-label={t.preview.closeTab(tab.label)}
-                  className="pointer-events-none absolute right-1.5 top-1/2 grid size-4 -translate-y-1/2 place-items-center rounded-sm text-(--ui-text-tertiary) opacity-0 transition-[background-color,color,opacity] hover:bg-(--ui-bg-secondary) hover:text-foreground focus-visible:pointer-events-auto focus-visible:opacity-100 group-hover/tab:pointer-events-auto group-hover/tab:opacity-100 group-focus-within/tab:pointer-events-auto group-focus-within/tab:opacity-100"
-                  onClick={() => closeRightRailTab(tab.id)}
-                  type="button"
-                >
-                  <Codicon name="close" size="0.75rem" />
-                </button>
-              </div>
+                    {active && (
+                      <span aria-hidden="true" className="absolute inset-x-0 top-0 h-px bg-(--ui-stroke-primary)" />
+                    )}
+                    <Tip label={tab.target.path || tab.target.url || tab.label}>
+                      <button
+                        aria-selected={active}
+                        className="flex h-full min-w-0 max-w-full items-center overflow-hidden pl-3 pr-2 text-left outline-none"
+                        onClick={() => selectRightRailTab(tab.id)}
+                        role="tab"
+                        type="button"
+                      >
+                        <span className="block min-w-0 truncate">{tab.label}</span>
+                      </button>
+                    </Tip>
+                    <span
+                      aria-hidden="true"
+                      className="pointer-events-none absolute inset-y-0 right-0 w-9 bg-[linear-gradient(to_right,transparent,var(--tab-bg)_55%)] opacity-0 transition-opacity group-hover/tab:opacity-100 group-focus-within/tab:opacity-100"
+                    />
+                    <button
+                      aria-label={t.preview.closeTab(tab.label)}
+                      className="pointer-events-none absolute right-1.5 top-1/2 grid size-4 -translate-y-1/2 place-items-center rounded-sm text-(--ui-text-tertiary) opacity-0 transition-[background-color,color,opacity] hover:bg-(--ui-bg-secondary) hover:text-foreground focus-visible:pointer-events-auto focus-visible:opacity-100 group-hover/tab:pointer-events-auto group-hover/tab:opacity-100 group-focus-within/tab:pointer-events-auto group-focus-within/tab:opacity-100"
+                      onClick={() => closeRightRailTab(tab.id)}
+                      type="button"
+                    >
+                      <Codicon name="close" size="0.75rem" />
+                    </button>
+                  </div>
+                </ContextMenuTrigger>
+                <ContextMenuContent>
+                  <ContextMenuItem onSelect={() => closeRightRailTab(tab.id)}>
+                    {t.common.close}
+                    <span className="ml-auto pl-4 text-(--ui-text-tertiary)">{formatCombo('mod+w')}</span>
+                  </ContextMenuItem>
+                  <ContextMenuItem disabled={!hasOthers} onSelect={() => closeOtherRightRailTabs(tab.id)}>
+                    {t.preview.closeOthers}
+                  </ContextMenuItem>
+                  <ContextMenuItem disabled={!hasTabsToRight} onSelect={() => closeRightRailTabsToRight(tab.id)}>
+                    {t.preview.closeToRight}
+                  </ContextMenuItem>
+                  <ContextMenuSeparator />
+                  <ContextMenuItem onSelect={closeRightRail}>{t.preview.closeAll}</ContextMenuItem>
+                </ContextMenuContent>
+              </ContextMenu>
             )
           })}
         </div>

apps/desktop/src/app/chat/sidebar/projects/workspace-header.tsx

@@ -19,7 +19,7 @@ import { useI18n } from '@/i18n'
 import { gitRef } from '@/lib/sanitize'
 import { cn } from '@/lib/utils'
 import { notifyError } from '@/store/notifications'
-import { copyPath, listRepoBranches, revealPath, startWorkInRepo } from '@/store/projects'
+import { copyPath, listRepoBranches, revealPath, startWorkInRepo, switchBranchInRepo } from '@/store/projects'
 
 import { SidebarCount, SidebarRowLead } from '../chrome'
 
@@ -41,6 +41,20 @@ function LaneLabel({ label, title }: { label: string; title?: string }) {
   )
 }
 
+interface BranchActionCopy {
+  branchCreateWorktree: string
+  branchOpenExisting: string
+  branchSwitchHome: string
+}
+
+const branchActionLabel = (branch: HermesGitBranch, copy: BranchActionCopy) => {
+  if (branch.checkedOut) {
+    return copy.branchOpenExisting
+  }
+
+  return branch.isDefault ? copy.branchSwitchHome : copy.branchCreateWorktree
+}
+
 // "+" affordance shared by repo and worktree headers — reveals on header hover.
 export function WorkspaceAddButton({ label, onClick }: { label: string; onClick: () => void }) {
   return (
@@ -120,14 +134,10 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
   const [open, setOpen] = useState(false)
   const [name, setName] = useState('')
   const [pending, setPending] = useState(false)
-  // "Convert an existing branch into a worktree" sub-mode: the body swaps the
-  // new-branch name input for a filterable list of the repo's branches.
   const [convertMode, setConvertMode] = useState(false)
   const [branches, setBranches] = useState<HermesGitBranch[]>([])
   const [branchesLoading, setBranchesLoading] = useState(false)
 
-  // Pull the repo's branches each time the picker is entered (cheap + bounded),
-  // so a branch created mid-session shows up.
   const loadBranches = useCallback(async () => {
     if (!repoPath) {
       return
@@ -170,7 +180,6 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
     }
   }
 
-  // Check an EXISTING branch out into a fresh worktree (no new branch).
   const convert = async (branch: HermesGitBranch) => {
     if (pending || !repoPath || !branch) {
       return
@@ -179,9 +188,16 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
     setPending(true)
 
     try {
-      const result = branch.worktreePath
-        ? { branch: branch.name, path: branch.worktreePath }
-        : await startWorkInRepo(repoPath, { existingBranch: branch.name })
+      let result: null | { branch: string; path: string }
+
+      if (branch.worktreePath) {
+        result = { branch: branch.name, path: branch.worktreePath }
+      } else if (branch.isDefault) {
+        await switchBranchInRepo(repoPath, branch.name)
+        result = { branch: branch.name, path: repoPath }
+      } else {
+        result = await startWorkInRepo(repoPath, { existingBranch: branch.name })
+      }
 
       if (result) {
         onStarted(result.path)
@@ -238,11 +254,9 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
                     >
                       <Codicon className="shrink-0 text-(--ui-text-tertiary)" name="git-branch" size="0.8rem" />
                       <span className="truncate">{branch.name}</span>
-                      {branch.checkedOut && (
-                        <span className="ml-auto shrink-0 text-[0.625rem] text-(--ui-text-tertiary)">
-                          {p.branchCheckedOut}
-                        </span>
-                      )}
+                      <span className="ml-auto shrink-0 text-[0.625rem] text-(--ui-text-tertiary)">
+                        {branchActionLabel(branch, p)}
+                      </span>
                     </CommandItem>
                   ))}
                 </CommandGroup>
@@ -268,8 +282,6 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
           )}
 
           {convertMode ? (
-            // The picker is a sub-screen: a single "Cancel" link steps back to
-            // the new-branch screen (the dialog's own ✕ / Esc still closes it).
             <DialogFooter className="sm:justify-start">
               <Button
                 className="px-0 text-(--ui-text-secondary) hover:text-foreground"
@@ -283,7 +295,6 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
             </DialogFooter>
           ) : (
             <DialogFooter className="sm:justify-between">
-              {/* Switch into the convert-an-existing-branch picker. */}
               <Button
                 className="px-0 text-(--ui-text-secondary) hover:text-foreground"
                 disabled={pending}

apps/desktop/src/global.d.ts

@@ -576,10 +576,12 @@ export interface HermesGitWorktree {
 }
 
 // A local branch as offered by the "convert a branch into a worktree" picker.
-// `checkedOut` marks branches git won't let a second worktree claim.
+// `checkedOut` means selecting opens that checkout; `isDefault` means selecting
+// switches the main checkout instead of creating `.worktrees/main`.
 export interface HermesGitBranch {
   name: string
   checkedOut: boolean
+  isDefault: boolean
   worktreePath: null | string
 }
 

apps/desktop/src/i18n/en.ts

@@ -1322,10 +1322,12 @@ export const en: Translations = {
       startWorkFailed: 'Could not create worktree',
       convertBranch: 'Convert a branch…',
       convertBranchTitle: 'Convert a branch',
-      convertBranchDesc: 'Check an existing branch out into a new worktree.',
+      convertBranchDesc: 'Open checked-out branches, or create a worktree for a free branch.',
       convertBranchPlaceholder: 'Search branches…',
       convertBranchInstead: 'Convert an existing branch',
-      branchCheckedOut: 'checked out',
+      branchOpenExisting: 'open',
+      branchSwitchHome: 'switch home',
+      branchCreateWorktree: 'new worktree',
       branchesLoading: 'Loading branches…',
       noBranches: 'No branches found',
       removeWorktree: 'Remove worktree',

apps/desktop/src/i18n/ja.ts

@@ -1446,10 +1446,12 @@ export const ja = defineLocale({
       startWorkFailed: 'ワークツリーを作成できませんでした',
       convertBranch: 'ブランチを変換…',
       convertBranchTitle: 'ブランチを変換',
-      convertBranchDesc: '既存のブランチを新しいワークツリーにチェックアウトします。',
+      convertBranchDesc: 'チェックアウト済みのブランチを開くか、空いているブランチのワークツリーを作成します。',
       convertBranchPlaceholder: 'ブランチを検索…',
       convertBranchInstead: '既存のブランチを変換',
-      branchCheckedOut: 'チェックアウト済み',
+      branchOpenExisting: '開く',
+      branchSwitchHome: 'ホームを切替',
+      branchCreateWorktree: '新しいワークツリー',
       branchesLoading: 'ブランチを読み込み中…',
       noBranches: 'ブランチが見つかりません',
       removeWorktree: 'ワークツリーを削除',

apps/desktop/src/i18n/types.ts

@@ -1076,7 +1076,9 @@ export interface Translations {
       convertBranchDesc: string
       convertBranchPlaceholder: string
       convertBranchInstead: string
-      branchCheckedOut: string
+      branchOpenExisting: string
+      branchSwitchHome: string
+      branchCreateWorktree: string
       branchesLoading: string
       noBranches: string
       removeWorktree: string

apps/desktop/src/i18n/zh-hant.ts

@@ -1399,10 +1399,12 @@ export const zhHant = defineLocale({
       startWorkFailed: '無法建立工作樹',
       convertBranch: '轉換分支…',
       convertBranchTitle: '轉換分支',
-      convertBranchDesc: '將現有分支簽出到新的工作樹。',
+      convertBranchDesc: '開啟已簽出的分支，或為可用分支建立工作樹。',
       convertBranchPlaceholder: '搜尋分支…',
       convertBranchInstead: '轉換現有分支',
-      branchCheckedOut: '已簽出',
+      branchOpenExisting: '開啟',
+      branchSwitchHome: '切回主簽出',
+      branchCreateWorktree: '新增工作樹',
       branchesLoading: '正在載入分支…',
       noBranches: '找不到分支',
       removeWorktree: '移除工作樹',

apps/desktop/src/i18n/zh.ts

@@ -1506,10 +1506,12 @@ export const zh: Translations = {
       startWorkFailed: '无法创建工作树',
       convertBranch: '转换分支…',
       convertBranchTitle: '转换分支',
-      convertBranchDesc: '将现有分支检出到新的工作树。',
+      convertBranchDesc: '打开已检出的分支，或为可用分支创建工作树。',
       convertBranchPlaceholder: '搜索分支…',
       convertBranchInstead: '转换现有分支',
-      branchCheckedOut: '已检出',
+      branchOpenExisting: '打开',
+      branchSwitchHome: '切回主检出',
+      branchCreateWorktree: '新工作树',
       branchesLoading: '正在加载分支…',
       noBranches: '未找到分支',
       removeWorktree: '移除工作树',