diff --git a/scripts/orchestrator-deploy-hook.sh b/scripts/orchestrator-deploy-hook.sh
index 75b855b..5d3d302 100755
--- a/scripts/orchestrator-deploy-hook.sh
+++ b/scripts/orchestrator-deploy-hook.sh
@@ -175,8 +175,21 @@ if [[ "${1:-}" == "--build-staging" ]]; then
     fi
     log "BUILD-STAGING: running health-check on port $TARGET_PORT (10x6s)"
     if health_check 10 6 "build-staging-health"; then
-        log "BUILD-STAGING: $TARGET_SERVICE healthy on the fresh image (exit 0)"
-        exit 0
+        log "BUILD-STAGING: $TARGET_SERVICE healthy on the fresh image"
+        # AC-4 / ADR-001 step 3: validate the EXACT fresh artefact that will be
+        # BUILD-ONCE retagged to prod by running staging_check.py against the
+        # freshly recreated STAGING stand (8501, never prod 8500 - AC-9).
+        # --mode stub: fast, deterministic, no LLM spend (ADR). Run INSIDE the
+        # container so B6 reads the running instance own env (.env.staging).
+        log "BUILD-STAGING: running staging_check.py --mode stub against fresh 8501 (port $TARGET_PORT)"
+        if docker exec "$TARGET_SERVICE" \\
+            python3 /repos/orchestrator/scripts/staging_check.py \\
+            --base-url "http://localhost:$TARGET_PORT" --mode stub >> "$LOG" 2>&1; then
+            log "BUILD-STAGING: staging_check --mode stub PASS on fresh image (exit 0)"
+            exit 0
+        fi
+        log "BUILD-STAGING: staging_check --mode stub FAILED on fresh image - not promoting (exit 1)"
+        exit 1
     fi
     log "BUILD-STAGING: health FAILED after rebuild (exit 1)"
     exit 1
diff --git a/tests/test_deploy_hook_provenance.py b/tests/test_deploy_hook_provenance.py
index 24416a1..b4652bb 100644
--- a/tests/test_deploy_hook_provenance.py
+++ b/tests/test_deploy_hook_provenance.py
@@ -95,6 +95,35 @@ def test_tc07_build_staging_recreates_and_health_checks_8501():
     assert "exit 1" in block
 
 
+def test_tc07_build_staging_runs_staging_check_stub_after_health():
+    """AC-4 / ADR-001 step 3: after the fresh staging container is healthy, the
+    --build-staging mode MUST run staging_check.py --mode stub against the fresh
+    8501 stand BEFORE reporting success, and fail-closed (exit 1) if it fails -
+    so the EXACT artefact promoted to prod is the one that passed staging."""
+    block = _build_staging_block()
+    # staging_check is invoked in --mode stub (fast, no LLM spend per ADR).
+    assert "staging_check.py" in block
+    assert "--mode stub" in block
+    # It targets the fresh STAGING stand (8501 / TARGET_PORT), never prod 8500.
+    assert '--base-url "http://localhost:$TARGET_PORT"' in block
+    # AC-9: the staging_check invocation must NOT hard-code the prod port (8500).
+    invocation_lines = [
+        ln for ln in block.splitlines()
+        if "staging_check.py" in ln or "--base-url" in ln
+    ]
+    assert invocation_lines, "expected a staging_check.py invocation line"
+    assert all("8500" not in ln for ln in invocation_lines)
+    # Ordering: staging_check runs AFTER the health-check, BEFORE the final exit 0.
+    health_idx = block.index('health_check 10 6 "build-staging-health"')
+    check_idx = block.index("staging_check.py")
+    assert health_idx < check_idx, "staging_check must run after health_check"
+    exit0_idx = block.index("staging_check --mode stub PASS")
+    success_exit = block.index("exit 0", exit0_idx)
+    assert check_idx < success_exit, "staging_check must precede the success exit 0"
+    # Fail-closed: a non-zero staging_check surfaces as exit 1 (no prod promote).
+    assert "staging_check --mode stub FAILED" in block
+
+
 # ---------------------------------------------------------------------------
 # TC-08: Dockerfile stamps the OCI revision label from a build-arg
 # ---------------------------------------------------------------------------