From 8e16d34dc7585eb5fe7778c5da7965e31460d601 Mon Sep 17 00:00:00 2001
From: Adam Moussa <166072409+amoussa1229@users.noreply.github.com>
Date: Thu, 16 Jul 2026 12:56:16 -0400
Subject: [PATCH] Fix WO fallback-rate alarm math expression (deploy hotfix)
 (#102)

The EmailProcessorTemplateFallbackRateAlarm added in #99 used
MAX([FILL(fb,0)+FILL(tmpl,0),1]) as a divide-by-zero guard, but
CloudWatch metric math has no element-wise MAX over an array; it
rejects the array operand at deploy time with 'Unsupported operand
type(s) for MAX', failing the WorkorderIngestStack update (it rolled
back cleanly). The outer IF((...)>=10, ...) volume floor already
guarantees a non-zero denominator in the true branch, so divide by
(FILL(fb,0)+FILL(tmpl,0)) directly and drop the invalid guard.

Unblocks the #99 deploy (PO stack already applied; WO rolled back).
---
 cdk/wo_stack.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/cdk/wo_stack.py b/cdk/wo_stack.py
index def3964..05d8ac2 100644
--- a/cdk/wo_stack.py
+++ b/cdk/wo_stack.py
@@ -418,8 +418,12 @@ class WorkorderIngestStack(Stack):
         )
         fallback_rate = cloudwatch.MathExpression(
             expression=(
+                # The IF volume floor (>=10) already guarantees the denominator
+                # is non-zero in the true branch, so divide directly. (An earlier
+                # MAX([...,1]) divide-by-zero guard used array syntax CloudWatch
+                # rejects at deploy: "Unsupported operand type(s) for MAX".)
                 "IF((FILL(fb,0)+FILL(tmpl,0))>=10, "
-                "100*FILL(fb,0)/MAX([FILL(fb,0)+FILL(tmpl,0),1]), 0)"
+                "100*FILL(fb,0)/(FILL(fb,0)+FILL(tmpl,0)), 0)"
             ),
             using_metrics={"fb": fb_metric, "tmpl": tmpl_metric},
             period=Duration.minutes(15),