CCM-12274: Added C4 & sequence diagrams for create/manage TTL that controls fallback to printing

Author: tdroza-nhs

docs/architecture/c4/ttl/create-ttl.md

@@ -0,0 +1,26 @@
+---
+layout: page
+title: Digital Letters - Printed Letter TTL Creation
+parent: Architecture
+nav_order: 1
+has_children: false
+is_not_draft: false
+last_modified_date: 2025-10-09
+owner: Tom D'Roza
+author: Tom D'Roza
+---
+
+```mermaid
+   architecture-beta
+    group createTtl(cloud)[Time_To_Live]
+
+    service db(logos:aws-dynamodb)[DynamoDB] in createTtl
+    service createLambda(logos:aws-lambda)[Create print ttl] in createTtl
+    service queue(logos:aws-sqs)[SQS] in createTtl
+    service storedEvent(logos:aws-eventbridge)[LetterStored event]
+    service scheduledEvent(logos:aws-eventbridge)[LetterPrintingScheduled event]
+
+    storedEvent:R --> L:queue
+    queue:R --> L:createLambda
+    createLambda:R --> L:db
+    db:R --> L:scheduledEvent

docs/architecture/c4/ttl/manage-ttl.md

@@ -0,0 +1,25 @@
+---
+layout: page
+title: Digital Letters - Printed Letter TTL Management
+parent: Architecture
+nav_order: 2
+has_children: false
+is_not_draft: false
+last_modified_date: 2025-10-09
+owner: Tom D'Roza
+author: Tom D'Roza
+---
+
+```mermaid
+architecture-beta
+   group manageTTL(cloud)[ManageTTL]
+   service manageLambda(logos:aws-lambda)[Poll TTL] in manageTTL
+   service manageDb(logos:aws-dynamodb)[DynamoDB] in manageTTL
+   service ttlStream(logos:aws-stream)[Stream] in manageTTL
+   service manageTtlExpiry(logos:aws-lambda)[handleTTLExpiry] in manageTTL
+   service printTTLExpired(logos:aws-eventbridge)[PrintTTLExpired] in manageTTL
+
+   manageLambda:R -- L:manageDb
+   manageDb:B -- T:ttlStream
+   ttlStream:R -- L:manageTtlExpiry
+   manageTtlExpiry:R -- L:printTTLExpired

docs/diagrams/create-print-ttl-sequence.md

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+---
+layout: page
+title: Fallback to Printing Sequence Diagram
+nav_order: 3
+parent: Diagrams
+has_children: false
+child_nav_order: reversed
+is_not_draft: false
+last_modified_date: 2025-10-08
+owner: Tom D'Roza
+author: Tom D'Roza
+---
+
+```mermaid
+sequenceDiagram
+  participant eb as Event Bridge
+  participant sqs as SQS
+  participant createTTL as Create TTL Lambda
+  participant dynamo as DynamoDB
+
+
+  eb ->> sqs: LetterStored event
+  sqs ->> createTTL:
+  createTTL ->> dynamo: Insert (24h TTL)
+```

docs/diagrams/digital-letters-flow.md

@@ -1,7 +1,7 @@
 ---
 layout: page
 title: Flow diagram
-nav_order: 2
+nav_order: 1
 parent: Diagrams
 has_children: false
 child_nav_order: reversed

docs/diagrams/digital-letters-sequence.md

@@ -1,6 +1,6 @@
 ---
 layout: page
-title: Sequence diagram
+title: Digital Letters Sequence diagram
 nav_order: 2
 parent: Diagrams
 has_children: false

docs/diagrams/expire-print-ttl-sequence.md

@@ -0,0 +1,32 @@
+---
+layout: page
+title: Fallback to Printing Sequence Diagram
+nav_order: 3
+parent: Diagrams
+has_children: false
+child_nav_order: reversed
+is_not_draft: false
+last_modified_date: 2025-10-08
+owner: Tom D'Roza
+author: Tom D'Roza
+---
+
+```mermaid
+sequenceDiagram
+  participant dynamo as DynamoDB
+  participant stream as DynamoDB Stream
+  participant expireTTL as Expire TTL Lambda
+  participant processTTLExpiry as Process TTL Expiry Lambda
+  participant eb as Event Bridge
+
+  alt Dynamo auto-expires after TTL
+    dynamo ->> dynamo: TTL expires
+    dynamo ->> stream: TTL expired
+    stream ->> processTTLExpiry:
+    processTTLExpiry ->> eb: PrintTTLExpired Event
+  else Polling Lamba expires after TTL
+    expireTTL ->> dynamo:
+    dynamo ->> stream: TTL expired
+    processTTLExpiry ->> eb: PrintTTLExpired Event
+  end
+```