test: re-align @sensitive test with fail-CLOSED contract after master merge

The auto-merge of master into this branch (commit 7875210) resolved
tests/test_protect_branches.py by taking master's side of the conflict,
leaving the old test_sensitive_runtime_init_failure_is_silent in place.
That test asserts @sensitive does NOT raise — but the production
change in commit 58263a1 (this branch) makes @sensitive raise
RuntimeError (fail-CLOSED, ADR-008). Result: CI ran the old assertion
against the new production code and failed.

Restore the renamed and re-asserted version of the test from commit
58263a1 — test_sensitive_runtime_init_failure_raises — so the test
asserts the new contract: RuntimeError is raised and __cause__ chains
the original exception.

runtime.py was resolved correctly by the auto-merge (both sides kept:
the new track_coverage / start_coverage_reporter / stop_coverage_reporter
/ _coverage_reporter_loop methods AND the existing bump_coverage_counter
are all present), so no changes there.

Author: maltsev-dev

tests/test_protect_branches.py

@@ -472,17 +472,30 @@ def my_charge(amount):
     assert "my_charge" in rt.get_sensitive_tools()
 
 
-def test_sensitive_runtime_init_failure_is_silent(test_runtime, monkeypatch):
-    """If runtime construction fails inside @sensitive, import must not crash."""
+def test_sensitive_runtime_init_failure_raises(test_runtime, monkeypatch):
+    """If runtime construction fails inside @sensitive, the decorator
+    MUST raise ``RuntimeError`` (fail-CLOSED, ADR-008). The original
+    exception is chained via ``__cause__`` so callers can still inspect
+    the root cause.
+    """
     from nullrun import decorators
 
-    monkeypatch.setattr(decorators, "_get_or_create_runtime", MagicMock(side_effect=RuntimeError("x")))
-    # Decorator must NOT raise even though registration failed.
-    @sensitive
-    def f():
-        return 1
+    original_exc = RuntimeError("x")
+    monkeypatch.setattr(
+        decorators,
+        "_get_or_create_runtime",
+        MagicMock(side_effect=original_exc),
+    )
+
+    with pytest.raises(
+        RuntimeError,
+        match=r"@sensitive registration failed for 'f'",
+    ) as excinfo:
+        @sensitive
+        def f():
+            return 1
 
-    assert f() == 1
+    assert excinfo.value.__cause__ is original_exc
 
 
 # ─── reset() ──────────────────────────────────────────────────────────