diff --git a/src/commands/list.ts b/src/commands/list.ts
index c7897d0..cdab9f8 100644
--- a/src/commands/list.ts
+++ b/src/commands/list.ts
@@ -46,6 +46,7 @@ export async function action(opts: { json?: boolean }) {
   // Determine status for each session in parallel
   const statusEntries = await Promise.all(
     sessions.map(async (s): Promise<[string, string]> => {
+      if (!(await git.isValidWorktree(s.worktree))) return [s.branch, "stale"]
       if (await vm.isClaudeActive(s.worktree, s.branch)) return [s.branch, "active"]
       const dirty = await git.isDirty(s.worktree)
       if (dirty) return [s.branch, "dirty"]
@@ -61,8 +62,8 @@ export async function action(opts: { json?: boolean }) {
     return
   }
 
-  const icons: Record<string, string> = { idle: `${dim}◯${reset}`, active: `${cyan}◎${reset}`, dirty: `${yellow}◐${reset}`, saved: `${green}●${reset}` }
-  const branchColors: Record<string, string> = { idle: dim, active: cyan, dirty: yellow, saved: green }
+  const icons: Record<string, string> = { idle: `${dim}◯${reset}`, active: `${cyan}◎${reset}`, dirty: `${yellow}◐${reset}`, saved: `${green}●${reset}`, stale: `${red}✖${reset}` }
+  const branchColors: Record<string, string> = { idle: dim, active: cyan, dirty: yellow, saved: green, stale: red }
   const branchWidth = Math.max(6, ...sessions.map((s) => s.branch.length))
   const cols = process.stdout.columns || 80
   const prefixWidth = branchWidth + 4
@@ -70,7 +71,7 @@ export async function action(opts: { json?: boolean }) {
   console.log(`  ${dim}${"BRANCH".padEnd(branchWidth)}  PROMPT${reset}`)
 
   for (const s of sessions) {
-    const prompt = (s.prompt ?? "").split("\n")[0]
+    const prompt = status === "stale" ? "broken worktree — close with -f to clean up" : (s.prompt ?? "").split("\n")[0]
     const status = statuses[s.branch]
     const icon = icons[status]
     const bc = branchColors[status]
@@ -79,7 +80,9 @@ export async function action(opts: { json?: boolean }) {
     console.log(`${icon} ${bc}${s.branch.padEnd(branchWidth)}${reset}  ${dim}${truncated}${reset}`)
   }
 
-  console.log(`\n${dim}◯ idle${reset} · ${cyan}◎ active${reset} · ${yellow}◐ unsaved${reset} · ${green}● saved${reset}`)
+  const hasStale = Object.values(statuses).includes("stale")
+  const legend = `${dim}◯ idle${reset} · ${cyan}◎ active${reset} · ${yellow}◐ unsaved${reset} · ${green}● saved${reset}`
+  console.log(`\n${legend}${hasStale ? ` · ${red}✖ stale${reset} (run ${dim}sandlot close -f <branch>${reset} to clean up)` : ""}`)
 
   if ((await vm.status()) !== "running") {
     console.log(`\n${red}VM is not running.${reset}`)
diff --git a/src/git.ts b/src/git.ts
index 6afb717..3379a28 100644
--- a/src/git.ts
+++ b/src/git.ts
@@ -189,6 +189,12 @@ export async function rebaseAbort(cwd: string): Promise<void> {
 }
 
 /** Check if a worktree has uncommitted changes. */
+/** Check if a worktree path is a valid git directory. */
+export async function isValidWorktree(worktreePath: string): Promise<boolean> {
+  const result = await $`git -C ${worktreePath} rev-parse --git-dir`.nothrow().quiet()
+  return result.exitCode === 0
+}
+
 export async function isDirty(worktreePath: string): Promise<boolean> {
   const result = await $`git -C ${worktreePath} status --porcelain`.nothrow().quiet()
   if (result.exitCode !== 0) return false
@@ -227,7 +233,8 @@ export async function fileDiff(ref1: string, ref2: string, file: string, cwd: st
 
 /** Check if a branch has commits beyond main. */
 export async function hasNewCommits(worktreePath: string): Promise<boolean> {
-  const main = await mainBranch(worktreePath)
+  let main: string
+  try { main = await mainBranch(worktreePath) } catch { return false }
   const result = await $`git -C ${worktreePath} rev-list ${main}..HEAD --count`.nothrow().quiet()
   if (result.exitCode !== 0) return false
   return parseInt(result.text().trim(), 10) > 0