diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa3466385..36888ea2a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,12 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Fixed
 
+- **Stale worktree branch cleanup on re-execute** (#7271): Re-executing a plan
+  after a failed attempt or diff review crashed with `fatal: a branch named
+  'cleveragents/plan-<id>' already exists`. Added `GitWorktreeSandbox.cleanup_stale()`
+  classmethod that idempotently removes stale worktree directories and branches
+  before creating a fresh sandbox.
+
 - **Worktree sandbox cleanup on plan cancel** (#9230): `plan cancel` now removes
   the git worktree branch and directory created during execute, preventing resource
   leaks from dangling worktrees. Delegates to `GitWorktreeSandbox.cleanup_stale()`
diff --git a/features/sandbox_reexecute_cleanup.feature b/features/sandbox_reexecute_cleanup.feature
new file mode 100644
index 000000000..7f126bc25
--- /dev/null
+++ b/features/sandbox_reexecute_cleanup.feature
@@ -0,0 +1,22 @@
+@sandbox-reexecute-cleanup
+Feature: Stale worktree branch cleanup before re-execute (#7271)
+  Verifies that re-executing a plan cleans up the stale worktree
+  branch from the previous execution before creating a fresh sandbox.
+
+  Scenario: cleanup_stale removes existing branch and worktree for srec
+    Given a temp git repo with a worktree branch for plan "01TESTREEXEC000000000000" for srec
+    When I call cleanup_stale for plan "01TESTREEXEC000000000000" for srec
+    Then the branch "cleveragents/plan-01TESTREEXEC000000000000" should not exist for srec
+    And the worktree directory should not exist for srec
+
+  Scenario: cleanup_stale is idempotent when no branch exists for srec
+    Given a temp git repo without any worktree branches for srec
+    When I call cleanup_stale for plan "01TESTNOEXIST00000000000" for srec
+    Then cleanup_stale should return False for srec
+
+  Scenario: create succeeds after cleanup_stale removes stale branch for srec
+    Given a temp git repo with a worktree branch for plan "01TESTRECREATE0000000000" for srec
+    When I call cleanup_stale for plan "01TESTRECREATE0000000000" for srec
+    And I create a fresh sandbox for plan "01TESTRECREATE0000000000" for srec
+    Then the fresh sandbox should be a directory for srec
+    And the branch "cleveragents/plan-01TESTRECREATE0000000000" should exist for srec
diff --git a/features/steps/sandbox_reexecute_cleanup_steps.py b/features/steps/sandbox_reexecute_cleanup_steps.py
new file mode 100644
index 000000000..69ce6b75e
--- /dev/null
+++ b/features/steps/sandbox_reexecute_cleanup_steps.py
@@ -0,0 +1,132 @@
+"""Steps for sandbox_reexecute_cleanup.feature."""
+
+from __future__ import annotations
+
+import os
+import shutil
+import subprocess
+import tempfile
+from pathlib import Path
+
+from behave import given, then, when
+
+
+def _git(args: list[str], cwd: str) -> subprocess.CompletedProcess[str]:
+    return subprocess.run(
+        ["git", *args],
+        cwd=cwd,
+        capture_output=True,
+        text=True,
+        check=True,
+        timeout=10,
+    )
+
+
+@given('a temp git repo with a worktree branch for plan "{plan_id}" for srec')
+def step_create_repo_with_branch(context: object, plan_id: str) -> None:
+    d = tempfile.mkdtemp(prefix="srec-")
+    context.add_cleanup(shutil.rmtree, d, True)
+    _git(["init", "-q", "-b", "main"], d)
+    _git(["config", "user.name", "T"], d)
+    _git(["config", "user.email", "t@t"], d)
+    _git(["config", "commit.gpgsign", "false"], d)
+    Path(d, "file.py").write_text("content\n")
+    _git(["add", "."], d)
+    _git(["commit", "-q", "-m", "init"], d)
+
+    # Create a worktree branch (simulating a previous execute)
+    branch = f"cleveragents/plan-{plan_id}"
+    wt_dir = tempfile.mkdtemp(prefix="srec-wt-")
+    context.add_cleanup(shutil.rmtree, wt_dir, True)
+    _git(["worktree", "add", "-b", branch, wt_dir, "HEAD"], d)
+
+    context.srec_repo = d
+    context.srec_wt_dir = wt_dir
+    context.srec_branch = branch
+
+
+@given("a temp git repo without any worktree branches for srec")
+def step_create_clean_repo(context: object) -> None:
+    d = tempfile.mkdtemp(prefix="srec-clean-")
+    context.add_cleanup(shutil.rmtree, d, True)
+    _git(["init", "-q", "-b", "main"], d)
+    _git(["config", "user.name", "T"], d)
+    _git(["config", "user.email", "t@t"], d)
+    _git(["config", "commit.gpgsign", "false"], d)
+    Path(d, "file.py").write_text("content\n")
+    _git(["add", "."], d)
+    _git(["commit", "-q", "-m", "init"], d)
+    context.srec_repo = d
+
+
+@when('I call cleanup_stale for plan "{plan_id}" for srec')
+def step_call_cleanup_stale(context: object, plan_id: str) -> None:
+    from cleveragents.infrastructure.sandbox.git_worktree import (
+        GitWorktreeSandbox,
+    )
+
+    context.srec_cleanup_result = GitWorktreeSandbox.cleanup_stale(
+        context.srec_repo,
+        plan_id,
+    )
+
+
+@when('I create a fresh sandbox for plan "{plan_id}" for srec')
+def step_create_fresh_sandbox(context: object, plan_id: str) -> None:
+    from cleveragents.infrastructure.sandbox.git_worktree import (
+        GitWorktreeSandbox,
+    )
+
+    sandbox = GitWorktreeSandbox(
+        resource_id="res-srec-test",
+        original_path=context.srec_repo,
+    )
+    ctx = sandbox.create(plan_id)
+    context.srec_fresh_sandbox = ctx.sandbox_path
+    context.srec_fresh_sandbox_obj = sandbox
+    context.add_cleanup(sandbox.cleanup)
+
+
+@then('the branch "{branch_name}" should not exist for srec')
+def step_branch_not_exists(context: object, branch_name: str) -> None:
+    result = subprocess.run(
+        ["git", "rev-parse", "--verify", f"refs/heads/{branch_name}"],
+        cwd=context.srec_repo,
+        capture_output=True,
+        check=False,
+        timeout=10,
+    )
+    assert result.returncode != 0, f"Branch {branch_name} still exists"
+
+
+@then('the branch "{branch_name}" should exist for srec')
+def step_branch_exists(context: object, branch_name: str) -> None:
+    result = subprocess.run(
+        ["git", "rev-parse", "--verify", f"refs/heads/{branch_name}"],
+        cwd=context.srec_repo,
+        capture_output=True,
+        check=False,
+        timeout=10,
+    )
+    assert result.returncode == 0, f"Branch {branch_name} does not exist"
+
+
+@then("the worktree directory should not exist for srec")
+def step_worktree_gone(context: object) -> None:
+    assert not os.path.exists(context.srec_wt_dir), (
+        f"Worktree directory still exists: {context.srec_wt_dir}"
+    )
+
+
+@then("cleanup_stale should return False for srec")
+def step_cleanup_returned_false(context: object) -> None:
+    assert context.srec_cleanup_result is False, (
+        f"Expected False but got {context.srec_cleanup_result}"
+    )
+
+
+@then("the fresh sandbox should be a directory for srec")
+def step_fresh_sandbox_is_dir(context: object) -> None:
+    assert os.path.isdir(context.srec_fresh_sandbox), (
+        f"Fresh sandbox is not a directory: {context.srec_fresh_sandbox}"
+    )