feat(desktop): base-branch picker for new worktree dialog

The sidebar "New worktree" button branched off whatever HEAD you were
on — now a filterable Popover+Command combobox lets you pick any local
or remote-tracking branch as the base, defaulting to origin/HEAD.

Backend listBaseBranches() queries refs/heads + refs/remotes via
for-each-ref, flags origin/HEAD (falling back to the local default for
no-remote repos). Mirrored on the Python REST API side
(base_branch_list + /api/git/base-branches route).

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

@@ -8,6 +8,7 @@ import test from 'node:test'
 import {
   addWorktree,
   ensureGitRepo,
+  listBaseBranches,
   listBranches,
   parseWorktrees,
   sanitizeBranch,
@@ -210,3 +211,53 @@ test('addWorktree: existing default branch switches the main checkout, not .work
     fs.rmSync(dir, { recursive: true, force: true })
   }
 })
+
+test('listBaseBranches: lists local branches and flags the default', async () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-base-branches-'))
+  const git = (...args) => execFileSync('git', args, { cwd: dir }).toString().trim()
+
+  try {
+    await ensureGitRepo('git', dir)
+    const trunk = git('branch', '--show-current')
+    execFileSync('git', ['branch', 'feature'], { cwd: dir })
+
+    const branches = await listBaseBranches(dir, 'git')
+    const names = branches.map(b => b.name).sort()
+
+    assert.deepEqual(names, [trunk, 'feature'].sort())
+    // No remote → all local.
+    assert.equal(branches.every(b => !b.isRemote), true)
+    // The trunk is flagged as the default.
+    assert.equal(branches.find(b => b.name === trunk).isDefault, true)
+    assert.equal(branches.find(b => b.name === 'feature').isDefault, false)
+  } finally {
+    fs.rmSync(dir, { recursive: true, force: true })
+  }
+})
+
+test('listBaseBranches: empty on a non-repo path', async () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-base-nonrepo-'))
+
+  try {
+    assert.deepEqual(await listBaseBranches(dir, 'git'), [])
+  } finally {
+    fs.rmSync(dir, { recursive: true, force: true })
+  }
+})
+
+test('addWorktree: base param branches off a specified local branch', async () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-base-add-'))
+  const git = (...args) => execFileSync('git', args, { cwd: dir }).toString().trim()
+
+  try {
+    await ensureGitRepo('git', dir)
+    execFileSync('git', ['branch', 'staging'], { cwd: dir })
+
+    const result = await addWorktree(dir, { base: 'staging', branch: 'new-from-staging', name: 'new-from-staging' }, 'git')
+
+    assert.equal(result.branch, 'new-from-staging')
+    assert.equal(git('-C', result.path, 'merge-base', 'HEAD', 'staging').length > 0, true)
+  } finally {
+    fs.rmSync(dir, { recursive: true, force: true })
+  }
+})

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

@@ -337,9 +337,56 @@ async function switchBranch(repoPath, branch, gitBin) {
   return { branch: target }
 }
 
+// Branches the new worktree can be based on: local heads + remote-tracking
+// refs. Listed most-recently-committed first; the remote's default branch
+// (origin/HEAD) is flagged so the UI can preselect it. Empty on a non-repo /
+// remote backend where the probe can't run.
+async function listBaseBranches(repoPath, gitBin) {
+  let resolved
+
+  try {
+    resolved = resolveRequestedPathForIpc(repoPath, { purpose: 'Base branch list' })
+  } catch {
+    return []
+  }
+
+  try {
+    const out = await runGit(
+      gitBin,
+      ['for-each-ref', '--format=%(refname:short)\t%(committerdate:iso)', '--sort=-committerdate', 'refs/heads', 'refs/remotes'],
+      resolved
+    )
+
+    const remoteDefault = await gitLine(gitBin, ['symbolic-ref', '--quiet', '--short', 'refs/remotes/origin/HEAD'], resolved)
+    const localDefault = await defaultBranch(gitBin, resolved)
+
+    return out
+      .split('\n')
+      .map(line => line.trim())
+      .filter(Boolean)
+      .map(line => {
+        const [name] = line.split('\t')
+
+        return {
+          name,
+          isRemote: name.startsWith('origin/'),
+          // origin/HEAD when a remote exists; otherwise the local default
+          // (main/master/init.defaultBranch) so a no-remote repo still flags
+          // its trunk.
+          isDefault: Boolean(
+            (remoteDefault && name === remoteDefault) || (!remoteDefault && localDefault && name === localDefault)
+          )
+        }
+      })
+  } catch {
+    return []
+  }
+}
+
 export {
   addWorktree,
   ensureGitRepo,
+  listBaseBranches,
   listBranches,
   listWorktrees,
   parseWorktrees,

apps/desktop/electron/main.ts

@@ -84,7 +84,7 @@ import {
   reviewUnstage
 } from './git-review-ops'
 import { gitRootForIpc } from './git-root'
-import { addWorktree, listBranches, listWorktrees, removeWorktree, switchBranch } from './git-worktree-ops'
+import { addWorktree, listBaseBranches, listBranches, listWorktrees, removeWorktree, switchBranch } from './git-worktree-ops'
 import {
   DATA_URL_READ_MAX_BYTES,
   DEFAULT_FETCH_TIMEOUT_MS,
@@ -8527,6 +8527,10 @@ ipcMain.handle('hermes:git:branchSwitch', async (_event, repoPath, branch) =>
 
 ipcMain.handle('hermes:git:branchList', async (_event, repoPath) => listBranches(repoPath, resolveGitBinary()))
 
+ipcMain.handle('hermes:git:baseBranchList', async (_event, repoPath) =>
+  listBaseBranches(repoPath, resolveGitBinary())
+)
+
 // Compact repo status (branch, ahead/behind, change counts + files) for the
 // composer coding rail. Returns null on a non-repo / remote backend so the rail
 // hides cleanly rather than erroring.

apps/desktop/electron/preload.ts

@@ -117,6 +117,7 @@ contextBridge.exposeInMainWorld('hermesDesktop', {
       ipcRenderer.invoke('hermes:git:worktreeRemove', repoPath, worktreePath, options),
     branchSwitch: (repoPath, branch) => ipcRenderer.invoke('hermes:git:branchSwitch', repoPath, branch),
     branchList: repoPath => ipcRenderer.invoke('hermes:git:branchList', repoPath),
+    baseBranchList: repoPath => ipcRenderer.invoke('hermes:git:baseBranchList', repoPath),
     repoStatus: repoPath => ipcRenderer.invoke('hermes:git:repoStatus', repoPath),
     fileDiff: (repoPath, filePath) => ipcRenderer.invoke('hermes:git:fileDiff', repoPath, filePath),
     scanRepos: (roots, options) => ipcRenderer.invoke('hermes:git:scanRepos', roots, options),

apps/desktop/src/app/chat/sidebar/projects/base-branch-picker.tsx

@@ -0,0 +1,160 @@
+import { useStore } from '@nanostores/react'
+import { useCallback, useEffect, useMemo, useState } from 'react'
+
+import { Button } from '@/components/ui/button'
+import { Codicon } from '@/components/ui/codicon'
+import { Command, CommandEmpty, CommandGroup, CommandInput, CommandItem, CommandList } from '@/components/ui/command'
+import { Popover, PopoverContent, PopoverTrigger } from '@/components/ui/popover'
+import type { HermesGitBaseBranch } from '@/global'
+import { useI18n } from '@/i18n'
+import { $repoStatus } from '@/store/coding-status'
+import { listBaseBranches } from '@/store/projects'
+
+// Filterable combobox for picking the base branch of a new worktree. Lists
+// local + remote-tracking branches, defaults to the default branch
+// (origin/HEAD, or local main/master when no remote). The current session's
+// branch is sorted to the top so it's one click away. The parent owns the
+// selected value via `value` / `onValueChange`.
+export function BaseBranchPicker({
+  disabled,
+  repoPath,
+  onValueChange,
+  value
+}: {
+  disabled?: boolean
+  repoPath: string
+  onValueChange: (value: string) => void
+  value: string
+}) {
+  const { t } = useI18n()
+  const p = t.sidebar.projects
+  const repoStatus = useStore($repoStatus)
+  const [branches, setBranches] = useState<HermesGitBaseBranch[]>([])
+  const [loading, setLoading] = useState(false)
+  const [open, setOpen] = useState(false)
+
+  const currentBranch = repoStatus?.detached ? null : (repoStatus?.branch ?? null)
+
+  const load = useCallback(async () => {
+    if (!repoPath) {
+      return
+    }
+
+    setLoading(true)
+
+    try {
+      const list = await listBaseBranches(repoPath)
+      setBranches(list)
+
+      // Default to the remote default (origin/HEAD). Fall back to the local
+      // default branch (main/master) when no remote exists. The value is
+      // always a concrete branch — never undefined.
+      const defaultBranch = list.find(b => b.isDefault)
+
+      if (defaultBranch) {
+        onValueChange(defaultBranch.name)
+      } else {
+        onValueChange(list[0]?.name ?? '')
+      }
+    } catch {
+      setBranches([])
+    } finally {
+      setLoading(false)
+    }
+  }, [repoPath, onValueChange])
+
+  // Load on mount so the default branch fills in before the user opens the
+  // popover — otherwise the button reads "branch off " with nothing after it.
+  useEffect(() => {
+    if (branches.length === 0 && !loading) {
+      void load()
+    }
+  }, [branches.length, loading, load])
+
+  // Pin the current session's branch to the top, keep the rest in git's
+  // most-recently-committed order.
+  const sorted = useMemo(() => {
+    if (!currentBranch) {
+      return branches
+    }
+
+    const idx = branches.findIndex(b => b.name === currentBranch)
+
+    if (idx <= 0) {
+      return branches
+    }
+
+    return [branches[idx], ...branches.slice(0, idx), ...branches.slice(idx + 1)]
+  }, [branches, currentBranch])
+
+  // The i18n function returns { before, after } so the branch name can be
+  // wrapped in its own styled (underlined) span — works for any word order.
+  const parts = p.branchOff()
+
+  return (
+    <div className="space-y-1.5">
+      <Popover
+        onOpenChange={next => {
+          if (next && branches.length === 0 && !loading) {
+            void load()
+          }
+
+          setOpen(next)
+        }}
+        open={open}
+      >
+        <PopoverTrigger asChild>
+          <Button
+            className="group w-full flex justify-start items-center min-w-0 gap-1.5 hover:no-underline hover:text-muted-foreground"
+            disabled={disabled || loading}
+            size="inline"
+            variant="text"
+          >
+            <Codicon className="shrink-0 text-(--ui-text-tertiary)" name="git-branch" size="0.8rem" />
+            <span className="shrink-0">{parts.before}</span>
+            <span className="shrink-0 text-primary underline-offset-4 decoration-current/20 group-hover:underline">
+              {loading ? '...' : value}
+            </span>
+            <Codicon className="shrink-0 text-(--ui-text-tertiary)" name="chevron-down" size="0.75rem" />
+            <span className="shrink-0">{parts.after}</span>
+          </Button>
+        </PopoverTrigger>
+        <PopoverContent align="start" className="z-[140] min-w-(--radix-popover-trigger-width) p-0">
+          <Command filter={(searchValue, search) => (searchValue.toLowerCase().includes(search.toLowerCase()) ? 1 : 0)}>
+            <CommandInput autoFocus placeholder={p.baseBranchPlaceholder} />
+            <CommandList className="max-h-64">
+              <CommandEmpty>{p.baseBranchNone}</CommandEmpty>
+              <CommandGroup>
+                {sorted.map(branch => (
+                  <CommandItem
+                    key={branch.name}
+                    onSelect={() => {
+                      onValueChange(branch.name)
+                      setOpen(false)
+                    }}
+                    value={branch.name}
+                  >
+                    <div className="flex items-center justify-start gap-1.5">
+                      <Codicon
+                        className="shrink-0 text-(--ui-text-tertiary)"
+                        name={branch.isRemote ? 'repo' : 'git-branch'}
+                        size="0.8rem"
+                      />
+                      {branch.isDefault && (
+                        <span className="ml-auto shrink-0 text-[0.625rem] text-(--ui-text-tertiary)">★</span>
+                      )}
+                      <span className="truncate">{branch.name}</span>
+                      {value === branch.name && (
+                        <Codicon className="ml-auto shrink-0 text-(--ui-accent)" name="check" size="0.8rem" />
+                      )}
+                    </div>
+                  </CommandItem>
+                ))}
+              </CommandGroup>
+            </CommandList>
+          </Command>
+        </PopoverContent>
+      </Popover>
+    </div>
+  )
+}

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

@@ -30,6 +30,8 @@ import { copyPath, listRepoBranches, revealPath, startWorkInRepo, switchBranchIn
 
 import { SidebarCount, SidebarRowLead } from '../chrome'
 
+import { BaseBranchPicker } from './base-branch-picker'
+
 // Branch/worktree labels routinely share a long prefix (`bb/coding-context-…`),
 // so plain end-truncation (`truncate`) hides exactly the suffix that tells two
 // lanes apart — both render as "bb/coding-context…". Keep the tail pinned and
@@ -142,6 +144,8 @@ export function WorkspaceMenu({ path, onRemove }: { path: null | string; onRemov
 // "New worktree": prompt for a branch name, then git spins up a fresh worktree
 // for that branch under the repo (the lightest way) and we open a new session
 // inside it. Naming is explicit — no auto-generated `hermes/work-<ts>` trees.
+// The base branch defaults to the remote default (origin/HEAD); the user can
+// pick any local or remote-tracking branch via a filterable combobox.
 export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onStarted: (path: string) => void }) {
   const { t } = useI18n()
   const s = t.sidebar
@@ -152,6 +156,7 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
   const [convertMode, setConvertMode] = useState(false)
   const [branches, setBranches] = useState<HermesGitBranch[]>([])
   const [branchesLoading, setBranchesLoading] = useState(false)
+  const [selectedBase, setSelectedBase] = useState('')
 
   const loadBranches = useCallback(async () => {
     if (!repoPath) {
@@ -181,7 +186,7 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
     try {
       // Pass the typed value as both the dir slug source and the branch, so the
       // branch is exactly what the user named (the dir is slugified git-side).
-      const result = await startWorkInRepo(repoPath, { branch, name: branch })
+      const result = await startWorkInRepo(repoPath, { base: selectedBase || undefined, branch, name: branch })
 
       if (result) {
         onStarted(result.path)
@@ -238,6 +243,7 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
         onClick={() => {
           setConvertMode(false)
           setName('')
+          setSelectedBase('')
           setOpen(true)
         }}
         type="button"
@@ -278,22 +284,30 @@ export function StartWorkButton({ repoPath, onStarted }: { repoPath: string; onS
               </CommandList>
             </Command>
           ) : (
-            <SanitizedInput
-              autoFocus
-              disabled={pending}
-              onKeyDown={event => {
-                if (event.key === 'Enter') {
-                  event.preventDefault()
-                  void submit()
-                } else if (event.key === 'Escape') {
-                  setOpen(false)
-                }
-              }}
-              onValueChange={setName}
-              placeholder={p.branchPlaceholder}
-              sanitize={gitRef}
-              value={name}
-            />
+            <>
+              <SanitizedInput
+                autoFocus
+                disabled={pending}
+                onKeyDown={event => {
+                  if (event.key === 'Enter') {
+                    event.preventDefault()
+                    void submit()
+                  } else if (event.key === 'Escape') {
+                    setOpen(false)
+                  }
+                }}
+                onValueChange={setName}
+                placeholder={p.branchPlaceholder}
+                sanitize={gitRef}
+                value={name}
+              />
+              <BaseBranchPicker
+                disabled={pending}
+                onValueChange={setSelectedBase}
+                repoPath={repoPath}
+                value={selectedBase}
+              />
+            </>
           )}
 
           {convertMode ? (

apps/desktop/src/global.d.ts

@@ -130,6 +130,10 @@ declare global {
         branchSwitch: (repoPath: string, branch: string) => Promise<{ branch: string }>
         // Local branches for the "convert a branch into a worktree" picker.
         branchList: (repoPath: string) => Promise<HermesGitBranch[]>
+        // Local + remote-tracking branches for the "base branch" picker in the
+        // new-worktree dialog. The remote default (origin/HEAD) is flagged so
+        // the UI can preselect it.
+        baseBranchList: (repoPath: string) => Promise<HermesGitBaseBranch[]>
         // Compact working-tree status for the composer coding rail. Null on a
         // non-repo / remote backend (where the Electron probe can't run).
         repoStatus: (repoPath: string) => Promise<HermesRepoStatus | null>
@@ -668,6 +672,16 @@ export interface HermesGitBranch {
   worktreePath: null | string
 }
 
+// A branch the new worktree can be based on: local heads + remote-tracking
+// refs. `isRemote` distinguishes `origin/main` from a local `main` (the UI
+// may show a remote glyph); `isDefault` flags origin/HEAD so the dialog can
+// preselect it.
+export interface HermesGitBaseBranch {
+  name: string
+  isRemote: boolean
+  isDefault: boolean
+}
+
 // A single changed path from `git status --porcelain=v2`, classified by state
 // so the coding rail / switcher can group + open the right diff.
 export interface HermesRepoStatusFile {

apps/desktop/src/i18n/en.ts

@@ -1585,6 +1585,9 @@ export const en: Translations = {
       newWorktreeTitle: 'New worktree',
       newWorktreeDesc: 'Name the branch for this worktree.',
       branchPlaceholder: 'e.g. my-feature',
+      branchOff: () => ({ after: '', before: 'branch off ' }),
+      baseBranchPlaceholder: 'Search branches…',
+      baseBranchNone: 'No branches found',
       startWorkFailed: 'Could not create worktree',
       convertBranch: 'Convert a branch…',
       convertBranchTitle: 'Convert a branch',

apps/desktop/src/i18n/ja.ts

@@ -1527,6 +1527,9 @@ export const ja = defineLocale({
       newWorktreeTitle: '新しいワークツリー',
       newWorktreeDesc: 'このワークツリーのブランチ名を入力してください。',
       branchPlaceholder: '例: my-feature',
+      branchOff: () => ({ after: ' から分岐', before: '' }),
+      baseBranchPlaceholder: 'ブランチを検索…',
+      baseBranchNone: 'ブランチが見つかりません',
       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',

apps/desktop/src/i18n/types.ts

@@ -1312,6 +1312,9 @@ export interface Translations {
       newWorktreeTitle: string
       newWorktreeDesc: string
       branchPlaceholder: string
+      branchOff: () => { after: string; before: string }
+      baseBranchPlaceholder: string
+      baseBranchNone: string
       startWorkFailed: string
       convertBranch: string
       convertBranchTitle: string

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

@@ -1479,6 +1479,9 @@ export const zhHant = defineLocale({
       newWorktreeTitle: '新增工作樹',
       newWorktreeDesc: '為這個工作樹命名分支。',
       branchPlaceholder: '例如 my-feature',
+      branchOff: () => ({ after: ' 分支', before: '從 ' }),
+      baseBranchPlaceholder: '搜尋分支…',
+      baseBranchNone: '未找到分支',
       startWorkFailed: '無法建立工作樹',
       convertBranch: '轉換分支…',
       convertBranchTitle: '轉換分支',

apps/desktop/src/i18n/zh.ts

@@ -1761,6 +1761,9 @@ export const zh: Translations = {
       newWorktreeTitle: '新建工作树',
       newWorktreeDesc: '为这个工作树命名分支。',
       branchPlaceholder: '例如 my-feature',
+      branchOff: () => ({ after: ' 分支', before: '从 ' }),
+      baseBranchPlaceholder: '搜索分支…',
+      baseBranchNone: '未找到分支',
       startWorkFailed: '无法创建工作树',
       convertBranch: '转换分支…',
       convertBranchTitle: '转换分支',

apps/desktop/src/lib/desktop-git.ts

@@ -1,4 +1,5 @@
 import type {
+  HermesGitBaseBranch,
   HermesGitBranch,
   HermesGitWorktree,
   HermesRepoStatus,
@@ -58,6 +59,9 @@ const remoteGit: GitBridge = {
   branchList: async repoPath =>
     (await gitGet<{ branches: HermesGitBranch[] }>('branches', { path: repoPath })).branches,
 
+  baseBranchList: async repoPath =>
+    (await gitGet<{ branches: HermesGitBaseBranch[] }>('base-branches', { path: repoPath })).branches,
+
   repoStatus: repoPath => gitGet<HermesRepoStatus | null>('status', { path: repoPath }),
 
   fileDiff: async (repoPath, filePath) =>

apps/desktop/src/store/projects.ts

@@ -1,7 +1,7 @@
 import { atom } from 'nanostores'
 
 import { liveSessionProjectId, type SidebarProjectTree } from '@/app/chat/sidebar/projects/workspace-groups'
-import type { HermesGitBranch } from '@/global'
+import type { HermesGitBaseBranch, HermesGitBranch } from '@/global'
 import { translateNow } from '@/i18n'
 import { desktopDefaultCwd, selectDesktopPaths, writeDesktopFileText } from '@/lib/desktop-fs'
 import { desktopGit } from '@/lib/desktop-git'
@@ -709,6 +709,19 @@ export async function listRepoBranches(repoPath: string): Promise<HermesGitBranc
   return git.branchList(repoPath)
 }
 
+// Local + remote-tracking branches for the base-branch picker in the
+// new-worktree dialog. The remote default (origin/HEAD) is flagged so the
+// UI can preselect it. Empty on a remote backend / non-repo.
+export async function listBaseBranches(repoPath: string): Promise<HermesGitBaseBranch[]> {
+  const git = desktopGit()
+
+  if (!git?.baseBranchList || !repoPath) {
+    return []
+  }
+
+  return git.baseBranchList(repoPath)
+}
+
 export async function switchBranchInRepo(repoPath: string, branch: string): Promise<void> {
   const git = desktopGit()
 

hermes_cli/web_git.py

@@ -644,3 +644,46 @@ def branch_switch(cwd: str, branch: str) -> dict:
         raise RuntimeError("Branch name is required.")
     _git_ok(cwd, ["switch", target])
     return {"branch": target}
+
+
+def base_branch_list(cwd: str) -> list[dict]:
+    """Local heads + remote-tracking refs for the base-branch picker.
+
+    The remote default (origin/HEAD) is flagged so the UI can preselect it.
+    """
+    out = _git_out(
+        cwd,
+        [
+            "for-each-ref",
+            "--format=%(refname:short)\t%(committerdate:iso)",
+            "--sort=-committerdate",
+            "refs/heads",
+            "refs/remotes",
+        ],
+    )
+    if not out:
+        return []
+    remote_default = _git_out(
+        cwd, ["symbolic-ref", "--quiet", "--short", "refs/remotes/origin/HEAD"]
+    ).strip()
+    local_default = _default_branch(cwd) if not remote_default else ""
+    result: list[dict] = []
+    for line in out.split("\n"):
+        line = line.strip()
+        if not line:
+            continue
+        name = line.split("\t")[0]
+        result.append(
+            {
+                "name": name,
+                "isRemote": name.startswith("origin/"),
+                # origin/HEAD when a remote exists; otherwise the local
+                # default (main/master/init.defaultBranch) so a no-remote
+                # repo still flags its trunk.
+                "isDefault": bool(
+                    (remote_default and name == remote_default)
+                    or (not remote_default and local_default and name == local_default)
+                ),
+            }
+        )
+    return result

hermes_cli/web_server.py

@@ -2333,6 +2333,11 @@ async def git_branches_route(path: str):
     return {"branches": await _git_op(_web_git.branch_list, _git_path(path))}
 
 
+@app.get("/api/git/base-branches")
+async def git_base_branches_route(path: str):
+    return {"branches": await _git_op(_web_git.base_branch_list, _git_path(path))}
+
+
 @app.get("/api/git/review/list")
 async def git_review_list_route(path: str, scope: str = "uncommitted", base: Optional[str] = None):
     return await _git_op(_web_git.review_list, _git_path(path), scope, base)