Bound /readyz so kubelet probes cannot hang the Service

/readyz walked the hash chain and opened pooled connections with no
libpq connect_timeout, so a 2s kubelet probe never saw a response and
the pod stayed unready. Informed Decision accept is blocked on that.

Probe health() only, under a 1.5s budget, publish last-known
tamper_evidence, and fail TCP handshake in 1s. Integrity stays on
/v1/integrity.

Assistant: grok
Assistant-Session: 01a0a182-bab7-7f11-b32b-d06f3af52082

tests/test_ingestion.py

@@ -1,5 +1,6 @@
 import io
 import json
+import time
 from datetime import datetime, timezone
 
 import pytest
@@ -502,6 +503,68 @@ def test_readiness_reports_recovery_fields_for_operational_backend():
     assert "platform-audit-storage" in body["recoverable_source"]
 
 
+def test_readyz_does_not_wait_on_chain_verification():
+    """Kubelet timeoutSeconds is 2; walking the hash chain is not a probe."""
+
+    class _ChainWalk(_BrokenBackend):
+        def health(self):
+            return None
+
+        @property
+        def retention_policy(self):
+            time.sleep(5)
+            raise AssertionError("/readyz must not call retention_policy")
+
+        def readiness_policy(self):
+            return RetentionPolicy(
+                custody_class="operational",
+                retention_days=None,
+                immutable=True,
+                tamper_evidence=False,
+                durable=True,
+                recoverable_days=30,
+                recoverable_source="cited",
+                recoverable_basis="measured",
+            )
+
+    started = time.monotonic()
+    status, body = invoke(
+        IngestionApplication(_ChainWalk(), "opaque"),
+        None, path="/readyz", method="GET", body=b"",
+    )
+    assert time.monotonic() - started < 1.0
+    assert status.startswith("200")
+    assert body["durable"] is True
+    assert body["tamper_evidence"] is False
+
+
+def test_readyz_treats_a_hung_health_check_as_unavailable():
+    class _HungHealth(_BrokenBackend):
+        def health(self):
+            time.sleep(5)
+
+    app = IngestionApplication(_HungHealth(), "opaque")
+    app._ready_budget = 0.05
+    started = time.monotonic()
+    status, body = invoke(app, None, path="/readyz", method="GET", body=b"")
+    assert time.monotonic() - started < 1.0
+    assert status.startswith("503")
+    assert body["status"] == "unavailable"
+
+
+def test_readyz_unavailable_backend_is_503():
+    class _Down(_BrokenBackend):
+        def health(self):
+            raise BackendUnavailableError("down")
+
+    status, body = invoke(
+        IngestionApplication(_Down(), "opaque"),
+        None, path="/readyz", method="GET", body=b"",
+    )
+    assert status.startswith("503")
+    assert body["status"] == "unavailable"
+
+
 def test_counters_track_each_outcome(tmp_path):
     app, _ = bound_app(tmp_path, may_read=True)
     invoke(app, event())                                   # accepted