lifecycle: guard Simulation.stream after a failed jet update; scope docs

A set_jet_amplitude failure while creating the internal stream marked the
Simulation failed, but the public stream property still retried
cuda.Stream(). Guard it like the other device-touching methods and add a
regression test (no retry, close still retryable). Lifecycle wording now
names the guarded device-touching methods; cached readers and host staging
stay callable. compatibility.md records the caller-visible fail-closed change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/test_jet_update_failure.py

@@ -10,6 +10,7 @@ import numpy as np
 import pytest
 
 pytest.importorskip("pycuda.driver")
+from CelerisLab import simulation as module
 from CelerisLab.body.jets import Jet, Radial, Sector
 from tests.unit.test_pinned_body_remap import ready
 from tests.unit.test_simulation_lifecycle import make_simulation
@@ -68,6 +69,30 @@ def test_simulation_upload_failure_keeps_host_and_blocks_reuse(monkeypatch):
     assert sim._closed and sim.ctx.is_closed
 
 
+def test_simulation_stream_creation_failure_fails_closed(monkeypatch):
+    sim, jet = simulation(monkeypatch)
+    created = []
+    def stream():
+        created.append(1)
+        raise RuntimeError("stream creation failed")
+    monkeypatch.setattr(module.cuda, "Stream", stream, raising=False)
+    sim._stream = None
+    with pytest.raises(RuntimeError, match="stream creation failed"):
+        sim.set_jet_amplitude(0, 2e-3)
+    assert sim.bodies.jets[0] is jet and sim._failed is not None
+    assert sim.field.curved.writes == [] and created == [1]
+    for call in (lambda: sim.stream, lambda: sim.set_jet_amplitude(0, 2e-3)):
+        with pytest.raises(RuntimeError, match="Simulation failed"):
+            call()
+    assert created == [1]  # the public stream property does not retry creation
+    sim.ctx.detach_failure = True
+    with pytest.raises(RuntimeError, match="detach failed"):
+        sim.close()
+    assert not sim._closed
+    sim.close()  # close stays retryable after the failure
+    assert sim._closed and sim.ctx.is_closed
+
+
 def test_simulation_before_initialize_commits_host_only(monkeypatch):
     sim, _ = simulation(monkeypatch)
     sim._initialized = False