fix(staging_check): B6 reads registry from running staging instance env

B6 false-FAILed because it built the project registry from the
launcher process-env via a host-path hack (sys.path.insert +
importlib.reload), not from the running staging instance. Run from the
host, ORCH_PROJECTS_JSON is unset -> default ET+ORCH registry -> false
FAIL -> spurious deploy-staging -> development rollback.

Variant (v) per ADR-001: remove the host-path hack; canonically run the
suite INSIDE orchestrator-staging via docker exec so src.projects
resolves from /app (PYTHONPATH) with .env.staging. Verdict logic
extracted into pure _evaluate_b6(known) -> (passed, detail) +
_known_project_ids_from_registry() / _run_b6() with deterministic FAIL on
source unavailability. deployer.md and STAGING_CHECK.md updated to the
docker exec command. src/projects.py, .env* and checks A/B4/B5/C
untouched.

Refs: ORCH-048

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_staging_check_b6.py

@@ -0,0 +1,151 @@
+"""ORCH-048: unit tests for the B6 registry-isolation verdict in staging_check.py.
+
+B6 «Registry: sandbox present, prod ET/ORCH absent» is the staging-isolation
+safety check. Its verdict logic is isolated into the pure function
+``_evaluate_b6(known) -> (passed, detail)`` so both outcomes (clean staging
+registry → PASS, polluted registry → FAIL) can be tested without standing up a
+live staging instance or docker (02-trz §9, ADR-001).
+
+These tests target that pure function plus the deterministic-degradation path
+(``_run_b6``) and statically assert the host-path hack is gone (TR-6 / TC-06).
+"""
+
+import importlib.util
+import pathlib
+
+import pytest
+
+# ---------------------------------------------------------------------------
+# Load scripts/staging_check.py by path (scripts/ is not an importable package).
+# ---------------------------------------------------------------------------
+_SCRIPT_PATH = (
+    pathlib.Path(__file__).resolve().parent.parent / "scripts" / "staging_check.py"
+)
+
+
+def _load_module():
+    spec = importlib.util.spec_from_file_location("staging_check", _SCRIPT_PATH)
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+sc = _load_module()
+
+SANDBOX = sc.SANDBOX_PROJECT_ID
+PROD_ET = sc.PROD_ET_PROJECT_ID
+PROD_ORCH = sc.PROD_ORCH_PROJECT_ID
+
+
+# ---------------------------------------------------------------------------
+# TC-01 — clean staging registry → PASS
+# ---------------------------------------------------------------------------
+def test_tc01_clean_registry_passes():
+    passed, detail = sc._evaluate_b6({SANDBOX})
+    assert passed is True
+    assert "sandbox=YES" in detail
+    assert "prod-ET=NO(good)" in detail
+    assert "prod-ORCH=NO(good)" in detail
+
+
+# ---------------------------------------------------------------------------
+# TC-02 — prod-ET leaked into registry → FAIL
+# ---------------------------------------------------------------------------
+def test_tc02_prod_et_present_fails():
+    passed, detail = sc._evaluate_b6({SANDBOX, PROD_ET})
+    assert passed is False
+    assert "sandbox=YES" in detail
+    assert "prod-ET=YES(BAD!)" in detail
+    assert "prod-ORCH=NO(good)" in detail
+
+
+# ---------------------------------------------------------------------------
+# TC-03 — prod-ORCH leaked into registry → FAIL
+# ---------------------------------------------------------------------------
+def test_tc03_prod_orch_present_fails():
+    passed, detail = sc._evaluate_b6({SANDBOX, PROD_ORCH})
+    assert passed is False
+    assert "sandbox=YES" in detail
+    assert "prod-ET=NO(good)" in detail
+    assert "prod-ORCH=YES(BAD!)" in detail
+
+
+# ---------------------------------------------------------------------------
+# TC-04 — sandbox absent (empty registry) → deterministic FAIL, no exception
+# ---------------------------------------------------------------------------
+def test_tc04_empty_registry_fails_without_sandbox():
+    passed, detail = sc._evaluate_b6(set())
+    assert passed is False
+    assert "sandbox=NO" in detail
+
+
+# ---------------------------------------------------------------------------
+# TC-05 — both prod projects leaked → FAIL
+# ---------------------------------------------------------------------------
+def test_tc05_both_prod_present_fails():
+    passed, detail = sc._evaluate_b6({SANDBOX, PROD_ET, PROD_ORCH})
+    assert passed is False
+    assert "prod-ET=YES(BAD!)" in detail
+    assert "prod-ORCH=YES(BAD!)" in detail
+
+
+# ---------------------------------------------------------------------------
+# TC-06 — registry source no longer depends on the host-path hack (TR-6)
+# ---------------------------------------------------------------------------
+def test_tc06_no_host_path_hack_in_source():
+    source = _SCRIPT_PATH.read_text(encoding="utf-8")
+    # The host-worktree path injection and the env-of-the-launcher reload that
+    # caused the false FAIL must be gone from the B6 mechanics.
+    assert 'sys.path.insert(0, "/repos/orchestrator")' not in source
+    assert "importlib.reload" not in source
+
+
+def test_tc06_registry_loader_uses_src_projects():
+    # The verdict input is built from src.projects.known_plane_project_ids()
+    # resolved via the running instance's own PYTHONPATH/env — not from a
+    # host-path-injected import. We verify the loader delegates to that function.
+    import src.projects as projects_mod
+
+    sentinel = {"sentinel-id"}
+    original = projects_mod.known_plane_project_ids
+    projects_mod.known_plane_project_ids = lambda: sentinel
+    try:
+        known = sc._known_project_ids_from_registry()
+    finally:
+        projects_mod.known_plane_project_ids = original
+    assert known == sentinel
+
+
+# ---------------------------------------------------------------------------
+# TC-07 — degraded registry source → deterministic FAIL (not false PASS, not raise)
+# ---------------------------------------------------------------------------
+def test_tc07_source_failure_is_deterministic_fail(monkeypatch):
+    def _boom():
+        raise RuntimeError("registry import blew up")
+
+    monkeypatch.setattr(sc, "_known_project_ids_from_registry", _boom)
+
+    results = sc.Results()
+    # Must not raise.
+    sc._run_b6(results)
+
+    assert len(results._items) == 1
+    label, passed, detail = results._items[0]
+    assert passed is False
+    assert "registry source unavailable" in detail
+    assert "registry import blew up" in detail
+
+
+# ---------------------------------------------------------------------------
+# _run_b6 happy path wiring (clean registry → PASS result recorded)
+# ---------------------------------------------------------------------------
+def test_run_b6_records_pass_for_clean_registry(monkeypatch):
+    monkeypatch.setattr(
+        sc, "_known_project_ids_from_registry", lambda: {SANDBOX}
+    )
+    results = sc.Results()
+    sc._run_b6(results)
+    assert len(results._items) == 1
+    _label, passed, detail = results._items[0]
+    assert passed is True
+    assert "sandbox=YES" in detail