Architecture decisions

Each record captures a decision that is hard to reverse, would surprise a newcomer, and came out of a real trade-off. Easily reversible or obvious choices are deliberately not recorded.

#	Decision
0001	The MCP gateway calls the Core Banking API over HTTP
0002	Lambda container images, not ECS Fargate
0003	PostgreSQL with pgvector is the single system of record
0004	Access tokens are validated in the application, not by API Gateway
0005	A NAT instance, not a NAT Gateway, provides egress
0006	Circuit breakers are per instance, with a shared force-open override
0007	Idempotency records are written in the same transaction as the business change
0008	Domain events leave through a transactional outbox onto SQS; no Kafka
0009	OpenAI embeddings, with full-text search as the degraded mode
0010	Deploy with GitHub Actions and CodeDeploy canaries, not CodePipeline
0011	Rows that reference a Transaction carry its initiated_at in a composite foreign key