feat: generate type-safe event publishers from AsyncAPI specs (#1320)

* feat: generate type-safe event publishers from AsyncAPI specs

Add a Go code generator (tools/gen-event-publishers/) that reads
AsyncAPI 3.0.0 YAML specs and generates typed event publisher packages
in gen/events/. Each generated Publisher wraps OutboxPublisher with
methods that accept the correct proto event type, topic, and event type
string, eliminating string-based configuration errors.

The generator validates proto types against actual .proto files,
skipping services whose proto definitions are not yet available
(audit, financial-accounting, market-information).

Generated packages: current_account (4 events), internal_account (2),
party (3), payment_order (7), position_keeping (9), reconciliation (6).

Also adds `make gen-event-publishers` Makefile target.

* fix: follow explicit $ref chain in event publisher generator

Resolve message-to-schema mapping through the explicit AsyncAPI $ref
chain (message -> component message -> payload schema) instead of
assuming message keys match schema names directly. Extract channel
message resolution into resolveChannelEvents to reduce cognitive
complexity. Iterate channel messages in sorted order for deterministic
output regardless of Go map iteration order.

Also add gen-event-publishers to Makefile help target.

* fix: clean stale gen/events packages before regeneration

Remove the output directory before generating publishers so that
removed or renamed AsyncAPI specs do not leave orphaned packages.

* fix: fail fast on spec errors and add diagnostic warnings

Fail with log.Fatalf instead of silently skipping when an AsyncAPI spec
file has read or parse errors. Add WARN log messages when $ref chains
resolve to unknown channels or component messages to surface spec drift.

---------

Co-authored-by: Ben Coombs <bjcoombs@users.noreply.github.com>

Author: bjcoombs

Makefile

@@ -32,7 +32,7 @@ GOMOD=$(GOCMD) mod
 GOGET=$(GOCMD) get
 GOFMT=$(GOCMD) fmt
 
-.PHONY: all help build seed-dev seed-dev-build test lint clean proto proto-v1 proto-v2 proto-openapi proto-lint proto-breaking proto-descriptors docker deploy-local fmt tidy deps coverage install proto-validate proto-deps-update proto-deps-graph proto-plugins-info validate-tilt validate-semconv validate-sagas proto-jsonschema validate-manifest-jsonschema validate-manifests control-plane-ci test-control-plane migrate-diff-all migrate-diff-current migrate-diff-position migrate-apply-all migrate-status-all migrate-lint-all migrate-hash-all migrate-apply-orgs migrate-status-orgs docs generate-saga-docs swagger-split swagger-ui dev-up dev-down dev-clean asyncapi
+.PHONY: all help build seed-dev seed-dev-build test lint clean proto proto-v1 proto-v2 proto-openapi proto-lint proto-breaking proto-descriptors docker deploy-local fmt tidy deps coverage install proto-validate proto-deps-update proto-deps-graph proto-plugins-info validate-tilt validate-semconv validate-sagas proto-jsonschema validate-manifest-jsonschema validate-manifests control-plane-ci test-control-plane migrate-diff-all migrate-diff-current migrate-diff-position migrate-apply-all migrate-status-all migrate-lint-all migrate-hash-all migrate-apply-orgs migrate-status-orgs docs generate-saga-docs swagger-split swagger-ui dev-up dev-down dev-clean asyncapi gen-event-publishers
 
 # Default target
 all: help
@@ -87,6 +87,7 @@ help:
 	@echo ""
 	@echo "Documentation targets:"
 	@echo "  make generate-saga-docs        - Generate Markdown and JSON Schema docs for saga handlers"
+	@echo "  make gen-event-publishers      - Generate typed event publishers from AsyncAPI specs"
 	@echo ""
 	@echo "API Explorer targets:"
 	@echo "  make swagger-split             - Split monolithic swagger into per-service files"
@@ -496,6 +497,10 @@ asyncapi:
 	@./scripts/gen-asyncapi.sh
 	@echo "AsyncAPI specs generated in api/asyncapi/"
 
+## gen-event-publishers: Generate typed event publishers from AsyncAPI specs
+gen-event-publishers:
+	@$(GOCMD) run ./tools/gen-event-publishers
+
 ## validate-manifests: Validate example manifests against protobuf schema, CEL, and Starlark
 validate-manifests:
 	@echo "Validating example manifests..."