diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6f4576f71..f65e85cfd 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -580,6 +580,17 @@ jobs:
             terraform -chdir="$d" test
           done
 
+      # The post-deploy /health gate and the GCP uptime check must read the
+      # body's top-level "status", not just the 200 (#649).
+      - name: Test /health gate modules
+        if: matrix.cloud == 'gcp'
+        run: |
+          for d in terraform/modules/deployment-checks terraform/modules/monitoring/gcp; do
+            terraform -chdir="$d" init -backend=false -lockfile=readonly -input=false
+            terraform -chdir="$d" fmt -check -recursive
+            terraform -chdir="$d" test
+          done
+
       - name: Terraform Init
         run: |
           cd terraform/environments/${{ matrix.cloud }}
diff --git a/internal/server/health_contract_test.go b/internal/server/health_contract_test.go
new file mode 100644
index 000000000..2dc252051
--- /dev/null
+++ b/internal/server/health_contract_test.go
@@ -0,0 +1,78 @@
+package server
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/LeanerCloud/cloud-commitments-platform/internal/api"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// topLevelHealthStatus decodes only the top-level "status" field, the way the
+// post-deploy check (jsondecode(body).status) and the GCP uptime check
+// (JSON path $.status) read it. It deliberately does not decode into
+// HealthStatus, so renaming the JSON tag breaks this test.
+func topLevelHealthStatus(t *testing.T, body []byte) string {
+	t.Helper()
+	var doc map[string]json.RawMessage
+	require.NoError(t, json.Unmarshal(body, &doc), "/health body must be a JSON object: %s", body)
+	raw, ok := doc["status"]
+	require.True(t, ok, "/health body must carry a top-level \"status\" field: %s", body)
+	var status string
+	require.NoError(t, json.Unmarshal(raw, &status), "top-level \"status\" must be a string: %s", body)
+	return status
+}
+
+// TestHealthBodyStatusIsTheVerdict pins the /health contract that
+// terraform/modules/deployment-checks and the GCP uptime check in
+// terraform/modules/monitoring/gcp gate on (#649): /health answers 200 even
+// when degraded (liveness, #488), so the only verdict a caller can rely on is
+// the top-level "status" field, which must read "healthy" only when the
+// replica is fully healthy, on both the server mux and the Lambda router.
+func TestHealthBodyStatusIsTheVerdict(t *testing.T) {
+	serveMux := func(t *testing.T, app *Application) (int, []byte) {
+		t.Helper()
+		req := httptest.NewRequestWithContext(context.Background(), http.MethodGet, "/health", nil)
+		w := httptest.NewRecorder()
+		CreateHTTPServer(app, 0).Handler.ServeHTTP(w, req)
+		return w.Code, w.Body.Bytes()
+	}
+
+	t.Run("server mux healthy", func(t *testing.T) {
+		code, body := serveMux(t, &Application{
+			Version: "test",
+			Config:  &mockConfigStoreForHealth{},
+			Auth:    createHealthyAuthService(),
+		})
+		assert.Equal(t, http.StatusOK, code)
+		assert.Equal(t, "healthy", topLevelHealthStatus(t, body))
+	})
+
+	t.Run("server mux degraded still answers 200", func(t *testing.T) {
+		// Auth store reachable, config store missing: a nested check still
+		// reads "healthy", which is why a substring match on the body is not
+		// a verdict.
+		code, body := serveMux(t, &Application{
+			Version: "test",
+			Auth:    createHealthyAuthService(),
+		})
+		assert.Equal(t, http.StatusOK, code, "/health is the liveness contract and must stay 200")
+		assert.Equal(t, "degraded", topLevelHealthStatus(t, body))
+		assert.Contains(t, string(body), `"healthy"`,
+			"a degraded body contains the string \"healthy\" in its nested checks; gates must read the top-level field")
+	})
+
+	t.Run("lambda router degraded still answers 200", func(t *testing.T) {
+		app := &Application{API: api.NewHandler(api.HandlerConfig{})}
+		event := `{"requestContext":{"http":{"method":"GET","path":"/health"}},"rawPath":"/health","headers":{}}`
+		resp, err := app.handleLambdaHTTPEvent(context.Background(), json.RawMessage(event))
+		require.NoError(t, err)
+		require.NotNil(t, resp)
+		assert.Equal(t, http.StatusOK, resp.StatusCode)
+		assert.Equal(t, "degraded", topLevelHealthStatus(t, []byte(resp.Body)))
+	})
+}
diff --git a/terraform/modules/deployment-checks/.terraform.lock.hcl b/terraform/modules/deployment-checks/.terraform.lock.hcl
index b799f46f7..0c9a1e107 100644
--- a/terraform/modules/deployment-checks/.terraform.lock.hcl
+++ b/terraform/modules/deployment-checks/.terraform.lock.hcl
@@ -2,8 +2,11 @@
 # Manual edits may be lost in future updates.
 
 provider "registry.terraform.io/hashicorp/http" {
-  version = "3.5.0"
+  version     = "3.5.0"
+  constraints = "~> 3.4"
   hashes = [
+    "h1:8bUoPwS4hahOvzCBj6b04ObLVFXCEmEN8T/5eOHmWOM=",
+    "h1:KsglDyFg9a9CIlOKxSSl8gDi+SAKfY+uvIZO1+SpeAc=",
     "h1:dl73+8wzQR++HFGoJgDqY3mj3pm14HUuH/CekVyOj5s=",
     "zh:047c5b4920751b13425efe0d011b3a23a3be97d02d9c0e3c60985521c9c456b7",
     "zh:157866f700470207561f6d032d344916b82268ecd0cf8174fb11c0674c8d0736",
diff --git a/terraform/modules/deployment-checks/main.tf b/terraform/modules/deployment-checks/main.tf
index 9aa47f31c..4f27b94cf 100644
--- a/terraform/modules/deployment-checks/main.tf
+++ b/terraform/modules/deployment-checks/main.tf
@@ -34,22 +34,40 @@ locals {
 # have scaled to zero after deployment.  Terraform check-block data sources
 # are evaluated *after* all resources are applied, so this resource warms the
 # container before checks and bash tests run.
+#
+# /health is a liveness endpoint: it answers HTTP 200 even while required
+# initialization is still pending or a dependency is down, and reports the
+# verdict in the body's top-level "status" field ("healthy" / "degraded").
+# Waiting only for a 200 would hand the checks below a replica that is up but
+# not initialized, so warmup waits for "status":"healthy" (#649). Without
+# python3 the body cannot be parsed and warmup falls back to waiting for 200.
 
 resource "terraform_data" "warmup" {
   triggers_replace = [var.api_base_url]
 
   provisioner "local-exec" {
     command = <<-EOT
+      body_file=$(mktemp)
+      trap 'rm -f "$body_file"' EXIT
       for i in 1 2 3 4 5 6 7 8 9 10; do
-        status=$(curl -sk -o /dev/null -w "%%{http_code}" --connect-timeout 10 --max-time 30 "${var.api_base_url}/health" 2>/dev/null) || status="000"
-        if [ "$status" != "000" ] && [ "$status" != "502" ] && [ "$status" != "503" ]; then
-          echo "Warmup: service ready (HTTP $status) after attempt $i"
-          exit 0
+        status=$(curl -sk -o "$body_file" -w "%%{http_code}" --connect-timeout 10 --max-time 30 "${var.api_base_url}/health" 2>/dev/null) || status="000"
+        if [ "$status" = "200" ]; then
+          if ! command -v python3 >/dev/null 2>&1; then
+            echo "Warmup: service answering (HTTP 200) after attempt $i; python3 not found, body status not checked"
+            exit 0
+          fi
+          health=$(python3 -c 'import json,sys; s=json.load(open(sys.argv[1])).get("status"); print(s if isinstance(s,str) else "")' "$body_file" 2>/dev/null) || health=""
+          if [ "$health" = "healthy" ]; then
+            echo "Warmup: service healthy after attempt $i"
+            exit 0
+          fi
+          echo "Warmup: attempt $i got HTTP 200 with status '$health', retrying in 5s..."
+        else
+          echo "Warmup: attempt $i got HTTP $status, retrying in 5s..."
         fi
-        echo "Warmup: attempt $i got HTTP $status, retrying in 5s..."
         sleep 5
       done
-      echo "Warmup: service did not become ready after 10 attempts, continuing anyway"
+      echo "Warmup: service did not report healthy after 10 attempts, continuing anyway"
     EOT
 
     on_failure = continue
@@ -79,6 +97,15 @@ check "health" {
     condition     = data.http.health.status_code == 200
     error_message = "Health check failed: ${var.api_base_url}/health returned ${data.http.health.status_code}"
   }
+
+  # /health answers 200 by design even when every dependency is down (it is
+  # the liveness contract, #488), so the status code alone passes on a fully
+  # degraded deployment. The verdict is the body's top-level "status" field,
+  # which both the server mux and the Lambda API router emit (#649).
+  assert {
+    condition     = try(jsondecode(data.http.health.response_body).status, "") == "healthy"
+    error_message = "Health check failed: ${var.api_base_url}/health reported status \"${try(tostring(jsondecode(data.http.health.response_body).status), "unparseable")}\", expected \"healthy\""
+  }
 }
 
 # --- Security Headers ---
diff --git a/terraform/modules/deployment-checks/tests/health.tftest.hcl b/terraform/modules/deployment-checks/tests/health.tftest.hcl
new file mode 100644
index 000000000..6c7458653
--- /dev/null
+++ b/terraform/modules/deployment-checks/tests/health.tftest.hcl
@@ -0,0 +1,125 @@
+# The post-deploy health gate must fail on a degraded deployment (#649).
+# /health answers HTTP 200 even when every dependency is down (liveness
+# contract, #488); the verdict is the body's top-level "status" field.
+#
+# Every check block reads a mocked http data source. Only data.http.health is
+# overridden per run; the others share the mock default (HTTP 200, "{}"), so
+# the checks that expect a non-200 status always fail here and are listed in
+# expect_failures. They are not what this file tests.
+mock_provider "http" {
+  mock_data "http" {
+    defaults = {
+      status_code      = 200
+      response_body    = "{}"
+      response_headers = {}
+    }
+  }
+}
+
+variables {
+  api_base_url  = "https://app.example.com"
+  provider_name = "gcp"
+}
+
+run "healthy_body_passes" {
+  command = plan
+
+  override_data {
+    target = data.http.health
+    values = {
+      status_code   = 200
+      response_body = "{\"timestamp\":\"2026-01-01T00:00:00Z\",\"checks\":{\"config_store\":{\"status\":\"healthy\"}},\"status\":\"healthy\",\"version\":\"test\"}"
+    }
+  }
+
+  expect_failures = [
+    check.security_headers,
+    check.auth_enforcement,
+    check.error_empty_body,
+    check.error_invalid_json,
+    check.method_post_summary,
+    check.content_type_xml,
+    check.content_type_missing,
+    check.request_size_limit,
+    check.frontend_serving,
+  ]
+}
+
+# The case the issue describes: the database is unreachable, /health still
+# answers 200, and the nested checks still contain the string "healthy".
+run "degraded_body_with_200_fails" {
+  command = plan
+
+  override_data {
+    target = data.http.health
+    values = {
+      status_code   = 200
+      response_body = "{\"timestamp\":\"2026-01-01T00:00:00Z\",\"checks\":{\"auth_store\":{\"status\":\"healthy\"},\"config_store\":{\"status\":\"unhealthy\",\"message\":\"config store unavailable\"}},\"status\":\"degraded\",\"version\":\"test\"}"
+    }
+  }
+
+  expect_failures = [
+    check.health,
+    check.security_headers,
+    check.auth_enforcement,
+    check.error_empty_body,
+    check.error_invalid_json,
+    check.method_post_summary,
+    check.content_type_xml,
+    check.content_type_missing,
+    check.request_size_limit,
+    check.frontend_serving,
+  ]
+}
+
+# A 200 whose body is not the health JSON (e.g. an SPA index served by a
+# catch-all route) must not pass either.
+run "non_json_body_fails" {
+  command = plan
+
+  override_data {
+    target = data.http.health
+    values = {
+      status_code   = 200
+      response_body = "<!doctype html><title>healthy</title>"
+    }
+  }
+
+  expect_failures = [
+    check.health,
+    check.security_headers,
+    check.auth_enforcement,
+    check.error_empty_body,
+    check.error_invalid_json,
+    check.method_post_summary,
+    check.content_type_xml,
+    check.content_type_missing,
+    check.request_size_limit,
+    check.frontend_serving,
+  ]
+}
+
+run "non_200_fails" {
+  command = plan
+
+  override_data {
+    target = data.http.health
+    values = {
+      status_code   = 503
+      response_body = "{\"status\":\"healthy\"}"
+    }
+  }
+
+  expect_failures = [
+    check.health,
+    check.security_headers,
+    check.auth_enforcement,
+    check.error_empty_body,
+    check.error_invalid_json,
+    check.method_post_summary,
+    check.content_type_xml,
+    check.content_type_missing,
+    check.request_size_limit,
+    check.frontend_serving,
+  ]
+}
diff --git a/terraform/modules/monitoring/gcp/main.tf b/terraform/modules/monitoring/gcp/main.tf
index 2ab1b5396..ebc5f9d81 100644
--- a/terraform/modules/monitoring/gcp/main.tf
+++ b/terraform/modules/monitoring/gcp/main.tf
@@ -617,9 +617,23 @@ resource "google_monitoring_uptime_check_config" "service_health" {
     }
   }
 
+  # /health answers 200 by design even when every dependency is down (it is
+  # the liveness contract, #488), so the verdict has to come from the body.
+  # Match the top-level "status" field exactly: a CONTAINS_STRING "healthy"
+  # matcher also matches "unhealthy" and every nested check's
+  # {"status":"healthy"}, so it passed on a degraded replica (#649). The check
+  # stays on /health, not /ready (pointing an uptime monitor at /ready would
+  # flap the alert on every deploy); service_unavailable below only fires
+  # after 180s of failures, so a replica that reports "degraded" briefly while
+  # it initializes does not page.
   content_matchers {
     content = "healthy"
-    matcher = "CONTAINS_STRING"
+    matcher = "MATCHES_JSON_PATH"
+
+    json_path_matcher {
+      json_path    = "$.status"
+      json_matcher = "EXACT_MATCH"
+    }
   }
 }
 
diff --git a/terraform/modules/monitoring/gcp/tests/uptime_check.tftest.hcl b/terraform/modules/monitoring/gcp/tests/uptime_check.tftest.hcl
new file mode 100644
index 000000000..7f5052533
--- /dev/null
+++ b/terraform/modules/monitoring/gcp/tests/uptime_check.tftest.hcl
@@ -0,0 +1,39 @@
+# The uptime check must tell "process alive" from "serving traffic" (#649).
+# /health answers HTTP 200 even when every dependency is down (liveness
+# contract, #488), so the check has to match the body's top-level "status"
+# exactly. A CONTAINS_STRING "healthy" matcher also matches "unhealthy" and
+# every nested check's {"status":"healthy"}, so it passed on a degraded replica.
+mock_provider "google" {}
+
+variables {
+  project_id     = "example-project"
+  service_name   = "cudly"
+  environment    = "dev"
+  db_instance_id = "cudly-db"
+  service_url    = "cudly.example.com"
+}
+
+run "uptime_check_matches_top_level_status" {
+  command = plan
+
+  assert {
+    condition     = google_monitoring_uptime_check_config.service_health.http_check[0].path == "/health"
+    error_message = "The uptime check must stay on /health (liveness); /ready answers 503 during every rollout and would flap the alert."
+  }
+
+  assert {
+    condition     = length(google_monitoring_uptime_check_config.service_health.content_matchers) == 1
+    error_message = "The uptime check needs exactly one content matcher on the /health body."
+  }
+
+  assert {
+    condition = alltrue([
+      for m in google_monitoring_uptime_check_config.service_health.content_matchers :
+      m.matcher == "MATCHES_JSON_PATH" && m.content == "healthy" &&
+      length(m.json_path_matcher) == 1 &&
+      m.json_path_matcher[0].json_path == "$.status" &&
+      m.json_path_matcher[0].json_matcher == "EXACT_MATCH"
+    ])
+    error_message = "The uptime check must exact-match \"healthy\" at JSON path $.status; a substring match on \"healthy\" also passes a degraded body."
+  }
+}