diff --git a/docs/owner-bootstrap.md b/docs/owner-bootstrap.md
index 0cc101a..8477769 100644
--- a/docs/owner-bootstrap.md
+++ b/docs/owner-bootstrap.md
@@ -11,6 +11,18 @@ There is no key fetch, alternate provider, key file, OAuth/HOME or daemon fallba
 `--check` validates local pins without a key, queue access or workload dispatch;
 it can advance the ledger's clock watermark but never initializes/reset its schema.
 
+**Rehearse before every paid attempt.** `--rehearse` (implies `--check`) also
+runs the admitted runtime's `rein-aharness` and `glas-harness` launchers, and
+`claude --version` when the build declares Claude, inside bwrap. The runtime is
+read-only at the sandbox mount path; there is no network, a cleared
+environment, no credentials, no provider route and no queue access. It writes
+nothing beyond what `--check` writes. The receipt lists each exit code and
+returns nonzero if any is not 0. The launcher check in `--check` reads only the
+first line of each launcher; the rehearsal executes them. Run 6efa9436
+(2026-09-27) failed with exit 127 on exactly such a launcher.
+
+    python -I -B -m rein_aharness.cli metered-once --owner-config /abs/owner.json --rehearse
+
 Use the standalone candidate interpreter as `python -I -B -m rein_aharness.cli`.
 `-I` excludes editable PYTHONPATH/user-site fallbacks; `-B` prevents bytecode writes
 from changing the complete artifact digest. The source and namespace rein commands
diff --git a/rein_aharness/cli.py b/rein_aharness/cli.py
index 4af738d..08bf89f 100644
--- a/rein_aharness/cli.py
+++ b/rein_aharness/cli.py
@@ -559,6 +559,8 @@ def main(argv: list[str] | None = None) -> int:
     )
     metered.add_argument("--owner-config", required=True, type=Path)
     metered.add_argument("--check", action="store_true", help="Validate local pins without claiming")
+    metered.add_argument("--rehearse", action="store_true",
+                         help="With --check: also run the runtime's launchers in bwrap, offline")
     metered.add_argument("--no-hub", action="store_true")
 
     claim_loop = sub.add_parser(
@@ -631,7 +633,8 @@ def main(argv: list[str] | None = None) -> int:
 
     if args.command == "metered-once":
         from rein_aharness.owner_bootstrap import run_once
-        return run_once(args.owner_config, check_only=args.check, report_to_hub=not args.no_hub)
+        return run_once(args.owner_config, check_only=args.check, report_to_hub=not args.no_hub,
+                        rehearse=args.rehearse)
     if args.command == "claim-loop":
         return _cmd_claim_loop(args)
 
diff --git a/rein_aharness/owner_bootstrap.py b/rein_aharness/owner_bootstrap.py
index 824538c..f96e4d3 100644
--- a/rein_aharness/owner_bootstrap.py
+++ b/rein_aharness/owner_bootstrap.py
@@ -99,10 +99,12 @@ def prepare(path: Path, config: OpsRunConfig) -> tuple[MessagesPolicy, Path, str
         raise BootstrapRefused("owner bootstrap configuration refused") from None
 
 
-def run_once(path: Path, *, check_only: bool = False, report_to_hub: bool = True) -> int:
+def run_once(path: Path, *, check_only: bool = False, report_to_hub: bool = True,
+             rehearse: bool = False) -> int:
     # Only this explicit exec-env child entry point consumes the conventional key.
     # Remove it before any subprocess or queue client can inherit it. No OAuth,
     # operator HOME, alternate provider URL or credential-file fallback is used.
+    check_only = check_only or rehearse
     provider_key = None if check_only else os.environ.get("ANTHROPIC_API_KEY")
     alternate_auth = None if check_only else os.environ.get("ANTHROPIC_AUTH_TOKEN")
     for name in ("ANTHROPIC_API_KEY", "ANTHROPIC_AUTH_TOKEN", "ANTHROPIC_BASE_URL"):
@@ -114,9 +116,16 @@ def run_once(path: Path, *, check_only: bool = False, report_to_hub: bool = True
         config = OpsRunConfig.from_env()
         policy, runtime_path, runtime_sha256 = prepare(path, config)
         if check_only:
-            print(json.dumps({"ok": True, "check_only": True, "dispatch_enabled": False,
-                              "policy_sha256": policy.sha256, "runtime_sha256": runtime_sha256}))
-            return 0
+            ok = True
+            receipt = {"check_only": True, "dispatch_enabled": False,
+                       "policy_sha256": policy.sha256, "runtime_sha256": runtime_sha256}
+            if rehearse:
+                from rein_aharness.owner_rehearsal import rehearse as rehearse_runtime
+                steps = rehearse_runtime(runtime_path)
+                ok = all(step.ok for step in steps)
+                receipt["rehearsal"] = {step.name: step.exit_code for step in steps}
+            print(json.dumps({"ok": ok, **receipt}))
+            return 0 if ok else 1
         if (alternate_auth or not isinstance(provider_key, str) or not provider_key
                 or len(provider_key) > 8192
                 or any(ord(c) < 33 or ord(c) > 126 for c in provider_key)):
diff --git a/rein_aharness/owner_rehearsal.py b/rein_aharness/owner_rehearsal.py
new file mode 100644
index 0000000..f753657
--- /dev/null
+++ b/rein_aharness/owner_rehearsal.py
@@ -0,0 +1,91 @@
+"""Free host rehearsal of an admitted owner runtime (REINAH-WP-0008-T01).
+
+The owner check reads only the first line of each launcher. The 2026-09-27
+run 6efa9436 passed that and still failed with exit 127, because a launcher
+re-executed a deleted build-host interpreter. This rehearsal runs the
+launchers the way the sandbox does: inside bwrap, with the runtime read-only
+at the mount path, no network, a cleared environment and nothing else
+writable. It uses no credentials, provider route, queue or ledger.
+"""
+
+from __future__ import annotations
+
+import json
+import shutil
+import subprocess
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Callable, Sequence
+
+RUNTIME_MOUNT = "/opt/sandboxer/runtime"
+# Same read-only system binds as sand-boxer's bwrap extension.
+SYSTEM_RO_BINDS = ("/usr", "/bin", "/lib", "/lib64", "/etc/resolv.conf", "/etc/ssl/certs")
+PYTHON_LAUNCHERS = ("rein-aharness", "glas-harness")
+TIMEOUT_SECONDS = 60
+
+Runner = Callable[[Sequence[str], int], int]
+
+
+@dataclass(frozen=True)
+class Step:
+    name: str
+    exit_code: int
+
+    @property
+    def ok(self) -> bool:
+        return self.exit_code == 0
+
+
+def bwrap_argv(runtime: Path, command: Sequence[str], *, bwrap_bin: str = "bwrap") -> list[str]:
+    argv = [
+        bwrap_bin,
+        "--unshare-user", "--unshare-pid", "--unshare-ipc",
+        "--unshare-uts", "--unshare-cgroup", "--unshare-net",
+        "--tmpfs", "/", "--proc", "/proc", "--dev", "/dev", "--clearenv",
+    ]
+    for path in SYSTEM_RO_BINDS:
+        if Path(path).exists():
+            argv += ["--ro-bind", path, path]
+    argv += [
+        "--dir", "/opt", "--dir", "/opt/sandboxer",
+        "--ro-bind", str(runtime), RUNTIME_MOUNT,
+        "--dir", "/tmp",
+        "--setenv", "HOME", "/tmp",
+        "--setenv", "PATH", f"{RUNTIME_MOUNT}/bin:/usr/bin:/bin",
+        "--chdir", "/tmp",
+    ]
+    return argv + list(command)
+
+
+def _run(argv: Sequence[str], timeout: int) -> int:
+    try:
+        return subprocess.run(
+            list(argv), stdin=subprocess.DEVNULL, stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL, timeout=timeout,
+        ).returncode
+    except subprocess.TimeoutExpired:
+        return 124
+    except OSError:
+        return 127
+
+
+def _expects_claude(runtime: Path) -> bool:
+    try:
+        info = json.loads((runtime / "build-info.json").read_text())
+    except (OSError, ValueError):
+        return False
+    return isinstance(info, dict) and isinstance(info.get("claude"), dict)
+
+
+def rehearse(runtime: Path, *, run: Runner = _run, bwrap_bin: str | None = None) -> list[Step]:
+    """Run each launcher once inside bwrap; return one step per launcher."""
+    bwrap = bwrap_bin or shutil.which("bwrap")
+    if bwrap is None:
+        return [Step("bwrap", 127)]
+    commands = [(name, [f"{RUNTIME_MOUNT}/bin/{name}", "--help"]) for name in PYTHON_LAUNCHERS]
+    if _expects_claude(runtime):
+        commands.append(("claude", [f"{RUNTIME_MOUNT}/bin/claude", "--version"]))
+    return [
+        Step(name, run(bwrap_argv(runtime, command, bwrap_bin=bwrap), TIMEOUT_SECONDS))
+        for name, command in commands
+    ]
diff --git a/tests/test_owner_bootstrap.py b/tests/test_owner_bootstrap.py
index 53d47fe..d211cff 100644
--- a/tests/test_owner_bootstrap.py
+++ b/tests/test_owner_bootstrap.py
@@ -149,3 +149,26 @@ def test_unexpected_exception_is_bounded(prepared, monkeypatch, capsys):
     monkeypatch.setattr("rein_aharness.claim_loop.process_one", MagicMock(side_effect=RuntimeError("fixture-key")))
     assert run_once(path) == 1
     assert json.loads(capsys.readouterr().out) == {"ok": False, "code": "owner_cycle_failed"}
+
+
+@pytest.mark.parametrize("exit_codes,code", [((0, 0), 0), ((0, 127), 1)])
+def test_rehearsal_reports_launcher_exits_and_never_claims_or_reads_key(
+        prepared, monkeypatch, capsys, exit_codes, code):
+    from rein_aharness.owner_rehearsal import Step
+    path, _, _, runtime = prepared
+    monkeypatch.setenv("ANTHROPIC_API_KEY", "fixture-owner-key")
+    seen = []
+    def fake(runtime_path):
+        seen.append(runtime_path)
+        return [Step(n, c) for n, c in zip(("rein-aharness", "glas-harness"), exit_codes)]
+    monkeypatch.setattr("rein_aharness.owner_rehearsal.rehearse", fake)
+    claimant = MagicMock()
+    monkeypatch.setattr("rein_aharness.claim_loop.process_one", claimant)
+    assert run_once(path, rehearse=True) == code
+    claimant.assert_not_called()
+    assert seen == [runtime]
+    out = json.loads(capsys.readouterr().out)
+    assert out["ok"] is (code == 0) and out["dispatch_enabled"] is False
+    assert out["rehearsal"] == {"rein-aharness": exit_codes[0], "glas-harness": exit_codes[1]}
+    assert "fixture-owner-key" not in json.dumps(out)
+    assert "ANTHROPIC_API_KEY" not in os.environ
diff --git a/tests/test_owner_rehearsal.py b/tests/test_owner_rehearsal.py
new file mode 100644
index 0000000..c2bbd69
--- /dev/null
+++ b/tests/test_owner_rehearsal.py
@@ -0,0 +1,78 @@
+"""Real bwrap rehearsal of owner runtimes (REINAH-WP-0008-T01)."""
+
+from __future__ import annotations
+
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+from rein_aharness.owner_rehearsal import RUNTIME_MOUNT, bwrap_argv, rehearse
+
+
+def _bwrap_usable() -> bool:
+    bwrap = shutil.which("bwrap")
+    if bwrap is None:
+        return False
+    probe = subprocess.run(bwrap_argv(Path("/usr"), ["/usr/bin/true"], bwrap_bin=bwrap),
+                           capture_output=True, timeout=30)
+    return probe.returncode == 0
+
+
+real_bwrap = pytest.mark.skipif(not _bwrap_usable(), reason="bwrap user namespaces unavailable")
+
+GOOD = f"#!{RUNTIME_MOUNT}/bin/python3\nimport sys\nsys.exit(0)\n"
+# uv's long-path trampoline that failed run 6efa9436: a shell script that
+# re-executes a build-host interpreter which no longer exists.
+BROKEN = "#!/bin/sh\n'''exec' '/old-build/bin/python3' \"$0\" \"$@\"\n' '''\nimport sys\n"
+
+
+def _runtime(tmp_path: Path, glas: str = GOOD) -> Path:
+    runtime = tmp_path / "runtime"
+    (runtime / "bin").mkdir(parents=True)
+    (runtime / "bin/python3").symlink_to("/usr/bin/python3")
+    for name, body in (("rein-aharness", GOOD), ("glas-harness", glas)):
+        launcher = runtime / "bin" / name
+        launcher.write_text(body)
+        launcher.chmod(0o755)
+    return runtime
+
+
+def test_argv_is_offline_read_only_and_credential_free(tmp_path):
+    argv = bwrap_argv(tmp_path, [f"{RUNTIME_MOUNT}/bin/rein-aharness", "--help"])
+    assert "--unshare-net" in argv and "--clearenv" in argv
+    assert "--bind" not in argv
+    i = argv.index(str(tmp_path))
+    assert argv[i - 1] == "--ro-bind" and argv[i + 1] == RUNTIME_MOUNT
+    assert not any("ANTHROPIC" in part or "/run/sandboxer" in part for part in argv)
+
+
+def test_missing_bwrap_fails_closed(tmp_path, monkeypatch):
+    monkeypatch.setattr("rein_aharness.owner_rehearsal.shutil.which", lambda name: None)
+    steps = rehearse(_runtime(tmp_path), run=lambda argv, timeout: 0)
+    assert [(s.name, s.ok) for s in steps] == [("bwrap", False)]
+
+
+def test_claude_is_rehearsed_only_when_the_build_declares_it(tmp_path):
+    runtime = _runtime(tmp_path)
+    calls = []
+    run = lambda argv, timeout: calls.append(argv[-2:]) or 0
+    assert [s.name for s in rehearse(runtime, run=run, bwrap_bin="bwrap")] == [
+        "rein-aharness", "glas-harness"]
+    (runtime / "build-info.json").write_text(json.dumps({"claude": {"expected_version": "x"}}))
+    assert [s.name for s in rehearse(runtime, run=run, bwrap_bin="bwrap")][-1] == "claude"
+    assert calls[-1] == [f"{RUNTIME_MOUNT}/bin/claude", "--version"]
+
+
+@real_bwrap
+def test_relocated_runtime_passes(tmp_path):
+    steps = rehearse(_runtime(tmp_path))
+    assert [(s.name, s.exit_code) for s in steps] == [("rein-aharness", 0), ("glas-harness", 0)]
+
+
+@real_bwrap
+def test_launcher_with_deleted_build_interpreter_fails_like_run_6efa9436(tmp_path):
+    steps = {s.name: s.exit_code for s in rehearse(_runtime(tmp_path, glas=BROKEN))}
+    assert steps == {"rein-aharness": 0, "glas-harness": 127}
diff --git a/workplans/REINAH-WP-0008-simpler-metered-retry.md b/workplans/REINAH-WP-0008-simpler-metered-retry.md
index 3e80e2b..633f080 100644
--- a/workplans/REINAH-WP-0008-simpler-metered-retry.md
+++ b/workplans/REINAH-WP-0008-simpler-metered-retry.md
@@ -46,17 +46,17 @@ once, run.
 
 ```task
 id: REINAH-WP-0008-T01
-status: todo
+status: done
 priority: high
 state_hub_task_id: "c6536c8d-7862-5de6-ad2b-401077b60c04"
 ```
 
-Add `rein-aharness owner check --rehearse <owner.json>`. It runs everything
-`metered-once --check` does. It then executes the admitted runtime's
-`rein-aharness` and `glas-harness` launchers inside bwrap, from the mount
-path, with `--unshare-all`, no credentials, no provider route and no ledger
-write. It also checks that the sandbox profile resolves. It prints a single
-pass or fail line with the runtime digest.
+Add a free rehearsal to the owner check. It runs everything
+`metered-once --check` does, then executes the admitted runtime's
+`rein-aharness` and `glas-harness` launchers inside bwrap from the mount
+path, with no network, credentials, provider route or ledger write. The
+sandbox profile is already resolved by `--check`. It prints one receipt with
+the runtime digest and each launcher's exit code.
 
 Today's launcher check reads only the first line of each launcher. This
 rehearsal runs them, the same way the failing run did.
@@ -67,6 +67,27 @@ relocated runtime. It must make no network calls and write nothing. The
 owner procedure in `docs/owner-bootstrap.md` makes the rehearsal a required
 step before any paid attempt.
 
+### Implemented — 2026-10-13
+
+`rein-aharness metered-once --owner-config <owner.json> --rehearse` (the flag
+implies `--check`, so it never reads a provider key or claims). The code is in
+`rein_aharness/owner_rehearsal.py`. It uses sand-boxer's isolation flags and
+read-only system binds, with the runtime read-only at `/opt/sandboxer/runtime`,
+`--unshare-net` and `--clearenv`. It runs each Python launcher with `--help`,
+plus `claude --version` when `build-info.json` declares Claude. A missing
+bwrap fails closed.
+
+Tests (`tests/test_owner_rehearsal.py`, `tests/test_owner_bootstrap.py`):
+
+- With real bwrap, a relocated runtime passes. The uv trampoline that
+  re-executes a deleted build interpreter fails with 127, as run `6efa9436`
+  did.
+- The rehearsal never claims and never reads the key.
+- The command line has no writable bind and no credential.
+
+The corrected runtime `ee3d0a53…` rehearses clean: rein-aharness 0,
+glas-harness 0, claude 0.
+
 ## B. Release holds that provably cost nothing
 
 ```task