Fix shared bucket check: add || true for set -e compatibility, fix cleanup message

All 7 tutorials with shared bucket check now handle:
- WITH stack: uses shared bucket, keeps it on cleanup
- WITHOUT stack: creates own bucket, deletes on cleanup
- Stack-only cleanup: ./cleanup-prereqs-bucket.sh --stack-only

Bug: describe-stacks returns non-zero when stack doesn't exist,
which triggers set -e. Fixed with || true in all 7 scripts.

Author: mwunderl

tuts/000-prereqs-bucket/cleanup-prereqs-bucket.sh

@@ -1,9 +1,12 @@
 #!/bin/bash
-# Empty and delete the shared tutorial S3 bucket, then delete the CloudFormation stack.
-# Usage: ./cfn/cleanup-bucket.sh
+# Clean up the shared tutorial S3 bucket and/or CloudFormation stack.
+# Usage: ./cleanup-prereqs-bucket.sh [--stack-only]
+#   --stack-only: delete the CFN stack but keep the bucket
 set -eo pipefail
 
 STACK_NAME="tutorial-prereqs-bucket"
+STACK_ONLY=false
+[ "$1" = "--stack-only" ] && STACK_ONLY=true
 
 BUCKET_NAME=$(aws cloudformation describe-stacks --stack-name "$STACK_NAME" \
     --query 'Stacks[0].Outputs[?OutputKey==`BucketName`].OutputValue' --output text 2>/dev/null)
@@ -13,6 +16,14 @@ if [ -z "$BUCKET_NAME" ] || [ "$BUCKET_NAME" = "None" ]; then
     exit 0
 fi
 
+if [ "$STACK_ONLY" = "true" ]; then
+    echo "Deleting stack only (keeping bucket: $BUCKET_NAME)"
+    aws cloudformation delete-stack --stack-name "$STACK_NAME"
+    aws cloudformation wait stack-delete-complete --stack-name "$STACK_NAME"
+    echo "Done. Stack deleted, bucket retained."
+    exit 0
+fi
+
 echo "Bucket: $BUCKET_NAME"
 echo ""
 echo "Contents:"

tuts/003-s3-gettingstarted/s3-gettingstarted.sh

@@ -22,7 +22,7 @@ fi
 UNIQUE_ID=$(cat /dev/urandom | tr -dc 'a-f0-9' | fold -w 12 | head -n 1)
 # Check for shared prereq bucket
 PREREQ_BUCKET=$(aws cloudformation describe-stacks --stack-name tutorial-prereqs-bucket \
-    --query 'Stacks[0].Outputs[?OutputKey==`BucketName`].OutputValue' --output text 2>/dev/null)
+    --query 'Stacks[0].Outputs[?OutputKey==`BucketName`].OutputValue' --output text 2>/dev/null || true)
 if [ -n "$PREREQ_BUCKET" ] && [ "$PREREQ_BUCKET" != "None" ]; then
     BUCKET_NAME="$PREREQ_BUCKET"
     BUCKET_IS_SHARED=true
@@ -92,9 +92,11 @@ cleanup() {
         done <<< "$DELETE_MARKERS_OUTPUT"
     fi
 
-    echo "Deleting bucket: ${BUCKET_NAME}"
     if [ "$BUCKET_IS_SHARED" = "false" ]; then
+        echo "Deleting bucket: ${BUCKET_NAME}"
         aws s3api delete-bucket --bucket "$BUCKET_NAME" 2>&1 || echo "WARNING: Failed to delete bucket ${BUCKET_NAME}"
+    else
+        echo "Keeping shared bucket: ${BUCKET_NAME}"
     fi
 
     echo ""
@@ -128,6 +130,7 @@ trap 'handle_error "line $LINENO"' ERR
 # ============================================================================
 
 echo "Step 1: Creating bucket ${BUCKET_NAME}..."
+if [ "$BUCKET_IS_SHARED" = "false" ]; then
 
 # CreateBucket requires LocationConstraint for all regions except us-east-1
 REGION="${AWS_REGION:-${AWS_DEFAULT_REGION:-${CONFIGURED_REGION}}}"
@@ -142,6 +145,7 @@ fi
 echo "$CREATE_OUTPUT"
 CREATED_RESOURCES+=("s3:bucket:${BUCKET_NAME}")
 echo "Bucket created."
+fi
 echo ""
 
 # ============================================================================