diff --git a/src/common/metrics/metrics.service.ts b/src/common/metrics/metrics.service.ts
new file mode 100644
index 0000000..08a7d68
--- /dev/null
+++ b/src/common/metrics/metrics.service.ts
@@ -0,0 +1,53 @@
+import { Injectable } from '@nestjs/common';
+
+/**
+ * Maximum allowed distinct values per metric label before collapsing to 'other' (#709).
+ * Prevents high-cardinality labels (wallet addresses, transaction IDs, UUIDs) from
+ * exploding Prometheus registry memory usage.
+ */
+export const MAX_LABEL_CARDINALITY = 100;
+
+const labelValuesSeen = new Map<string, Set<string>>();
+
+/**
+ * Bounds the cardinality of metric label values to prevent memory leaks (#709).
+ */
+export function sanitizeMetricLabelValue(labelName: string, value: string): string {
+  if (!value) return 'unknown';
+
+  // Sanitize UUIDs / hex hashes / wallet addresses directly to 'redacted_id'
+  if (/^[a-fA-F0-9-]{36}$/.test(value) || /^G[A-Z2-7]{55}$/.test(value)) {
+    return 'redacted_id';
+  }
+
+  let seen = labelValuesSeen.get(labelName);
+  if (!seen) {
+    seen = new Set<string>();
+    labelValuesSeen.set(labelName, seen);
+  }
+
+  if (seen.has(value)) {
+    return value;
+  }
+
+  if (seen.size >= MAX_LABEL_CARDINALITY) {
+    return 'other';
+  }
+
+  seen.add(value);
+  return value;
+}
+
+@Injectable()
+export class MetricsService {
+  /**
+   * Sanitizes a metric label set before recording to Prometheus.
+   */
+  sanitizeLabels(labels: Record<string, string>): Record<string, string> {
+    const sanitized: Record<string, string> = {};
+    for (const [key, value] of Object.entries(labels)) {
+      sanitized[key] = sanitizeMetricLabelValue(key, value);
+    }
+    return sanitized;
+  }
+}
diff --git a/src/common/utils/config.utils.ts b/src/common/utils/config.utils.ts
new file mode 100644
index 0000000..84a418e
--- /dev/null
+++ b/src/common/utils/config.utils.ts
@@ -0,0 +1,33 @@
+/**
+ * Strict boolean environment variable parser (#706).
+ *
+ * Rejects arbitrary strings (e.g. "random_string", "2", "enabled") that JS Boolean()
+ * would incorrectly evaluate as true.
+ *
+ * Valid truthy strings: "true", "1", "yes", "on"
+ * Valid falsy strings: "false", "0", "no", "off"
+ *
+ * Throws an Error on invalid boolean configuration strings.
+ */
+export function parseBooleanEnv(value: unknown, defaultValue = false): boolean {
+  if (value === undefined || value === null || value === "") {
+    return defaultValue;
+  }
+
+  if (typeof value === "boolean") {
+    return value;
+  }
+
+  if (typeof value === "string") {
+    const trimmed = value.trim().toLowerCase();
+    if (["true", "1", "yes", "on"].includes(trimmed)) {
+      return true;
+    }
+    if (["false", "0", "no", "off"].includes(trimmed)) {
+      return false;
+    }
+    throw new Error(`Invalid boolean configuration value: "${value}". Allowed values are true, false, 1, 0, yes, no, on, off.`);
+  }
+
+  throw new Error(`Invalid boolean configuration type: ${typeof value}`);
+}
diff --git a/src/policy/policy.controller.ts b/src/policy/policy.controller.ts
index fb4752b..f03fc30 100644
--- a/src/policy/policy.controller.ts
+++ b/src/policy/policy.controller.ts
@@ -476,8 +476,19 @@ export class PolicyController {
       // periodic write fails once the peer is gone, and both that and a
       // normal disconnect fire 'close' on the request, which completes the
       // stream and runs the teardown below.
-      const heartbeat = setInterval(() => {
+      // #708 — re-validate policy authorization on heartbeat to reject revoked credentials.
+      const heartbeat = setInterval(async () => {
         if (!subscriber.closed) {
+          try {
+            const currentPolicy = await this.policy.getPolicy(id);
+            if (!currentPolicy || currentPolicy.policyholder !== authedWallet) {
+              subscriber.error(new ForbiddenException('Policy authorization revoked'));
+              cleanup();
+              return;
+            }
+          } catch {
+            /* ignore transient DB read errors during heartbeat */
+          }
           subscriber.next({ type: 'heartbeat', data: { timestamp: Date.now() } });
         }
       }, SSE_HEARTBEAT_INTERVAL_MS);