diff --git a/README.md b/README.md
index 98033c3..6954744 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,7 @@ Coupa PO emails are received at `amazon_po@int.seahaven.com`, parsed by Claude H
 |---|---|---|
 | `po-email-processor` | S3 ObjectCreated | Claude extraction + DynamoDB write |
 | `po-ingest-site-extractor` | DynamoDB Streams | Site code/address extraction -> `verified-sites` |
-| `po-web-ui` | Function URL | HTML dashboard |
+| `po-web-ui` | Manual invoke | HTML dashboard (public Function URL removed 2026-06-08, INFRA-74) |
 
 **Tables:**
 - `purchase-orders` (PK: `po_number`, Streams: NEW_IMAGE) — shared with seahaven-slack-bot (read-only; see Shared Resources)
@@ -49,7 +49,7 @@ Amazon APM work order emails (from Hexagon EAM / HxGN SmartCloud) are received a
 | Function | Trigger | Purpose |
 |---|---|---|
 | `workorder-email-processor` | S3 ObjectCreated | Claude extraction + DynamoDB write |
-| `workorder-web-ui` | Function URL | HTML dashboard |
+| `workorder-web-ui` | Manual invoke | HTML dashboard (public Function URL removed 2026-06-08, INFRA-74) |
 
 **Tables:**
 - `WorkOrders` (PK: `work_order_id`, GSIs: `site-code-index`, `status-index`)
@@ -67,6 +67,8 @@ All Lambdas: Python 3.12, ARM64, 60-day log retention.
 
 **SES:** Both stacks add rules to the shared `INBOUND_MAIL` receipt rule set on `int.seahaven.com`.
 
+**Failure handling (INFRA-41):** Each email-processor is async-invoked (S3 → Lambda). Both have a CDK-managed SQS dead-letter queue (`dead_letter_queue=`, 14-day retention, SSL-enforced) so a failed parse is captured rather than silently dropped after Lambda's retries, plus an ALARM-only CloudWatch `Errors` alarm (Sum, threshold > 0) wired to the shared `site-alerts` SNS topic.
+
 ## Shared Resources
 
 ### `purchase-orders` table (owned here)
diff --git a/cdk/po_stack.py b/cdk/po_stack.py
index cf0ea33..144d9e9 100644
--- a/cdk/po_stack.py
+++ b/cdk/po_stack.py
@@ -5,6 +5,8 @@ from aws_cdk import (
     Duration,
     RemovalPolicy,
     Stack,
+    aws_cloudwatch as cloudwatch,
+    aws_cloudwatch_actions as cw_actions,
     aws_dynamodb as dynamodb,
     aws_lambda as lambda_,
     aws_lambda_event_sources as lambda_event_sources,
@@ -14,6 +16,8 @@ from aws_cdk import (
     aws_ses as ses,
     aws_ses_actions as ses_actions,
     aws_secretsmanager as secretsmanager,
+    aws_sns as sns,
+    aws_sqs as sqs,
 )
 from constructs import Construct
 
@@ -58,6 +62,18 @@ class PoIngestStack(Stack):
             removal_policy=RemovalPolicy.RETAIN,
         )
 
+        # --- DLQ for failed async invocations (INFRA-41 / audit H-8) ---
+        # SES → S3 → Lambda is async; without an OnFailure destination a failed
+        # parse (bad email, transient error) is silently dropped after Lambda's
+        # retries. CDK generates the queue name to avoid colliding with the
+        # interim CLI-created po-email-processor-dlq (removed post-deploy).
+        email_processor_dlq = sqs.Queue(
+            self,
+            "EmailProcessorDlq",
+            retention_period=Duration.days(14),
+            enforce_ssl=True,
+        )
+
         # --- Lambda function ---
         email_processor = lambda_.Function(
             self,
@@ -82,6 +98,7 @@ class PoIngestStack(Stack):
             timeout=Duration.seconds(60),
             memory_size=256,
             log_retention=logs.RetentionDays.TWO_MONTHS,
+            dead_letter_queue=email_processor_dlq,
             environment={
                 "PO_TABLE": "purchase-orders",
                 "ANTHROPIC_API_KEY_SECRET_ARN": anthropic_secret.secret_arn,
@@ -93,6 +110,29 @@ class PoIngestStack(Stack):
         po_table.grant_read_write_data(email_processor)
         anthropic_secret.grant_read(email_processor)
 
+        # --- Errors alarm (INFRA-41 / audit H-8) ---
+        # ALARM-only (no OK action, per the CloudWatch-alarm preference) to the
+        # shared site-alerts topic (CMK alias/seahaven-alarm-topics lives on the
+        # topic). Any errored invocation in a 5-min window pages.
+        alarm_topic = sns.Topic.from_topic_arn(
+            self,
+            "SiteAlertsTopic",
+            f"arn:aws:sns:{self.region}:{self.account}:site-alerts",
+        )
+        email_processor.metric_errors(
+            period=Duration.minutes(5),
+            statistic="Sum",
+        ).create_alarm(
+            self,
+            "EmailProcessorErrorsAlarm",
+            alarm_name="po-email-processor-errors",
+            alarm_description="po-email-processor async invocation errors",
+            threshold=0,
+            evaluation_periods=1,
+            comparison_operator=cloudwatch.ComparisonOperator.GREATER_THAN_THRESHOLD,
+            treat_missing_data=cloudwatch.TreatMissingData.NOT_BREACHING,
+        ).add_alarm_action(cw_actions.SnsAction(alarm_topic))
+
         # S3 event notification → Lambda
         email_bucket.add_event_notification(
             s3.EventType.OBJECT_CREATED,
@@ -138,14 +178,10 @@ class PoIngestStack(Stack):
 
         po_table.grant_read_data(web_ui)
 
-        # Function URL for direct access
-        web_url = web_ui.add_function_url(
-            auth_type=lambda_.FunctionUrlAuthType.NONE,
-        )
-
-        cdk.CfnOutput(
-            self, "WebUIUrl", value=web_url.url, description="PO Dashboard URL"
-        )
+        # Public Function URL removed 2026-06-08 (INFRA-74 / audit C-5): the
+        # unauthenticated FunctionUrlAuthType.NONE URL was deleted out-of-band
+        # via CLI. Removing the construct (and its auto-generated Principal:*
+        # invoke permission) reconciles IaC with the live state.
 
         # --- Verified sites table (extracted from PO ship-to addresses) ---
         verified_sites_table = dynamodb.Table(
diff --git a/cdk/wo_stack.py b/cdk/wo_stack.py
index 37355ac..4cba41b 100644
--- a/cdk/wo_stack.py
+++ b/cdk/wo_stack.py
@@ -5,6 +5,8 @@ from aws_cdk import (
     Duration,
     RemovalPolicy,
     Stack,
+    aws_cloudwatch as cloudwatch,
+    aws_cloudwatch_actions as cw_actions,
     aws_dynamodb as dynamodb,
     aws_lambda as lambda_,
     aws_logs as logs,
@@ -13,6 +15,8 @@ from aws_cdk import (
     aws_ses as ses,
     aws_ses_actions as ses_actions,
     aws_secretsmanager as secretsmanager,
+    aws_sns as sns,
+    aws_sqs as sqs,
 )
 from constructs import Construct
 
@@ -73,6 +77,18 @@ class WorkorderIngestStack(Stack):
             removal_policy=RemovalPolicy.RETAIN,
         )
 
+        # --- DLQ for failed async invocations (INFRA-41 / audit H-8) ---
+        # SES → S3 → Lambda is async; without an OnFailure destination a failed
+        # parse (bad email, transient error) is silently dropped after Lambda's
+        # retries. CDK generates the queue name to avoid colliding with the
+        # interim CLI-created workorder-email-processor-dlq (removed post-deploy).
+        email_processor_dlq = sqs.Queue(
+            self,
+            "EmailProcessorDlq",
+            retention_period=Duration.days(14),
+            enforce_ssl=True,
+        )
+
         # --- Lambda function ---
         email_processor = lambda_.Function(
             self,
@@ -97,6 +113,7 @@ class WorkorderIngestStack(Stack):
             timeout=Duration.seconds(60),
             memory_size=256,
             log_retention=logs.RetentionDays.TWO_MONTHS,
+            dead_letter_queue=email_processor_dlq,
             environment={
                 "WORK_ORDERS_TABLE": work_orders_table.table_name,
                 "COMMENTS_TABLE": comments_table.table_name,
@@ -110,6 +127,29 @@ class WorkorderIngestStack(Stack):
         comments_table.grant_read_write_data(email_processor)
         anthropic_secret.grant_read(email_processor)
 
+        # --- Errors alarm (INFRA-41 / audit H-8) ---
+        # ALARM-only (no OK action, per the CloudWatch-alarm preference) to the
+        # shared site-alerts topic (CMK alias/seahaven-alarm-topics lives on the
+        # topic). Any errored invocation in a 5-min window pages.
+        alarm_topic = sns.Topic.from_topic_arn(
+            self,
+            "SiteAlertsTopic",
+            f"arn:aws:sns:{self.region}:{self.account}:site-alerts",
+        )
+        email_processor.metric_errors(
+            period=Duration.minutes(5),
+            statistic="Sum",
+        ).create_alarm(
+            self,
+            "EmailProcessorErrorsAlarm",
+            alarm_name="workorder-email-processor-errors",
+            alarm_description="workorder-email-processor async invocation errors",
+            threshold=0,
+            evaluation_periods=1,
+            comparison_operator=cloudwatch.ComparisonOperator.GREATER_THAN_THRESHOLD,
+            treat_missing_data=cloudwatch.TreatMissingData.NOT_BREACHING,
+        ).add_alarm_action(cw_actions.SnsAction(alarm_topic))
+
         # S3 event notification -> Lambda
         email_bucket.add_event_notification(
             s3.EventType.OBJECT_CREATED,
@@ -156,11 +196,7 @@ class WorkorderIngestStack(Stack):
         work_orders_table.grant_read_data(web_ui)
         comments_table.grant_read_data(web_ui)
 
-        # Function URL for direct access
-        web_url = web_ui.add_function_url(
-            auth_type=lambda_.FunctionUrlAuthType.NONE,
-        )
-
-        cdk.CfnOutput(
-            self, "WebUIUrl", value=web_url.url, description="Work Order Dashboard URL"
-        )
+        # Public Function URL removed 2026-06-08 (INFRA-74 / audit C-5): the
+        # unauthenticated FunctionUrlAuthType.NONE URL was deleted out-of-band
+        # via CLI. Removing the construct (and its auto-generated Principal:*
+        # invoke permission) reconciles IaC with the live state.