refactor: Remove platform_ref inheritance from saga definitions (#2141)

* refactor: Remove platform_ref inheritance from saga definitions

Delete the platform_ref inheritance system including override API,
platform sync, similarity matching, version pinning, and fallback
resolution. Simplify Definition struct by removing PlatformRef,
OverrideReason, PlatformVersionAtOverride, ResolvedScript, and
UsedPlatformFallback fields. Script is now required directly on
all saga definitions.

- Delete 12 files (override_api, similarity, migrate_platform_ref,
  fallback_resolution, platform_sync, version_pinning + tests)
- Remove platform_ref columns from SQL queries and scan functions
- Simplify CreateDraft INSERT and activation validation
- Move ComputeScriptHash to registry.go, humanizeName/regex to seeder.go
- Update orchestrators to use Script instead of ResolvedScript
- Remove PlatformSagaVersionID from shared SagaInstance model
- Add migration to drop platform_ref columns and set script NOT NULL
- Update test DDL to match simplified schema

* fix: Address CodeRabbit review feedback

- Add NULL script backfill guard before SET NOT NULL in migration
- Add empty script guard in ValidateSagaDraft handler
- Add comment explaining why remove_platform_ref migration is excluded
  from setupPlatformTestDB (targets tenant tables, not public schema)

* fix: Reject empty-script updates and include migration in test setup

- Add handler-level guard rejecting explicit empty-script updates in
  UpdateSagaDefinition (InvalidArgument if script is set to "")
- Create saga_definition with old schema in setupPlatformTestDB so the
  remove_platform_ref migration exercises the full migration chain

---------

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

Author: bjcoombs

services/current-account/service/coverage_unit_test.go

@@ -2026,12 +2026,12 @@ func TestResolveWithdrawalScript_SagaNotFound(t *testing.T) {
 	_ = script
 }
 
-func TestResolveDepositScript_ResolvedScriptEmpty(t *testing.T) {
-	// Test path where resolver returns a definition but with empty ResolvedScript
+func TestResolveDepositScript_ScriptEmpty(t *testing.T) {
+	// Test path where resolver returns a definition but with empty Script
 	mockRegistry := &stubSagaRegistry{
 		getActiveResult: &refsaga.Definition{
-			Name:           "deposit",
-			ResolvedScript: "", // Empty - should fall back
+			Name:   "deposit",
+			Script: "", // Empty - should fall back
 		},
 	}
 
@@ -2061,11 +2061,11 @@ func TestResolveDepositScript_ResolvedScriptEmpty(t *testing.T) {
 	assert.Equal(t, "default_deposit()", script)
 }
 
-func TestResolveDepositScript_ResolvedScriptPresent(t *testing.T) {
+func TestResolveDepositScript_ScriptPresent(t *testing.T) {
 	mockRegistry := &stubSagaRegistry{
 		getActiveResult: &refsaga.Definition{
-			Name:           "deposit",
-			ResolvedScript: "custom_deposit()",
+			Name:   "deposit",
+			Script: "custom_deposit()",
 		},
 	}
 
@@ -2095,11 +2095,11 @@ func TestResolveDepositScript_ResolvedScriptPresent(t *testing.T) {
 	assert.Equal(t, "custom_deposit()", script)
 }
 
-func TestResolveWithdrawalScript_ResolvedScriptEmpty(t *testing.T) {
+func TestResolveWithdrawalScript_ScriptEmpty(t *testing.T) {
 	mockRegistry := &stubSagaRegistry{
 		getActiveResult: &refsaga.Definition{
-			Name:           "withdrawal",
-			ResolvedScript: "",
+			Name:   "withdrawal",
+			Script: "",
 		},
 	}
 	accountTypeCache := cache.NewLocalAccountTypeCache(
@@ -2128,11 +2128,11 @@ func TestResolveWithdrawalScript_ResolvedScriptEmpty(t *testing.T) {
 	assert.Equal(t, "default_withdrawal()", script)
 }
 
-func TestResolveWithdrawalScript_ResolvedScriptPresent(t *testing.T) {
+func TestResolveWithdrawalScript_ScriptPresent(t *testing.T) {
 	mockRegistry := &stubSagaRegistry{
 		getActiveResult: &refsaga.Definition{
-			Name:           "withdrawal",
-			ResolvedScript: "custom_withdrawal()",
+			Name:   "withdrawal",
+			Script: "custom_withdrawal()",
 		},
 	}
 	accountTypeCache := cache.NewLocalAccountTypeCache(

services/current-account/service/deposit_orchestrator.go

@@ -323,7 +323,7 @@ func (o *DepositOrchestrator) resolveClearingAccountID(ctx context.Context, curr
 // Resolution order:
 //  1. If SagaResolver is configured and the account has a ProductTypeCode, resolve the
 //     saga definition from the registry using ProductTypeSagaResolver. The definition's
-//     ResolvedScript is used. If the resolver returns ErrSagaNotFound, the error is
+//     Script is used. If the resolver returns ErrSagaNotFound, the error is
 //     propagated (fail-fast: a prefixed product type must have a corresponding saga).
 //  2. Otherwise, fall back to the static default DepositScript.
 func (o *DepositOrchestrator) resolveDepositScript(ctx context.Context, account domain.CurrentAccount) (string, error) {
@@ -333,25 +333,25 @@ func (o *DepositOrchestrator) resolveDepositScript(ctx context.Context, account
 
 	tenantID, ok := tenant.FromContext(ctx)
 	if !ok {
-		// No tenant context — fall back to static script
+		// No tenant context - fall back to static script
 		return o.depositScript, nil
 	}
 
 	def, err := o.sagaResolver.ResolveForProductType(ctx, tenantID, account.ProductTypeCode(), "deposit")
 	if err != nil {
 		if errors.Is(err, refsaga.ErrSagaNotFound) {
-			// Prefix is defined but no saga found — fail fast per PRD convention
+			// Prefix is defined but no saga found - fail fast per PRD convention
 			return "", err
 		}
-		// ErrNotFound (product type or generic saga missing) — fall back to static script
+		// ErrNotFound (product type or generic saga missing) - fall back to static script
 		o.logger.Warn("saga resolution fell through to default deposit script",
 			"product_type_code", account.ProductTypeCode(),
 			"error", err)
 		return o.depositScript, nil
 	}
 
-	if def.ResolvedScript == "" {
-		// Definition has no resolved script — fall back to static script
+	if def.Script == "" {
+		// Definition has no script - fall back to static script
 		o.logger.Warn("resolved saga definition has no script, using default",
 			"saga_name", def.Name,
 			"product_type_code", account.ProductTypeCode())
@@ -361,5 +361,5 @@ func (o *DepositOrchestrator) resolveDepositScript(ctx context.Context, account
 	o.logger.Debug("using product-type-specific deposit saga",
 		"saga_name", def.Name,
 		"product_type_code", account.ProductTypeCode())
-	return def.ResolvedScript, nil
+	return def.Script, nil
 }

services/current-account/service/withdrawal_orchestrator.go

@@ -296,7 +296,7 @@ func (o *WithdrawalOrchestrator) resolveClearingAccountID(ctx context.Context, c
 // Resolution order:
 //  1. If SagaResolver is configured and the account has a ProductTypeCode, resolve the
 //     saga definition from the registry using ProductTypeSagaResolver. The definition's
-//     ResolvedScript is used. If the resolver returns ErrSagaNotFound, the error is
+//     Script is used. If the resolver returns ErrSagaNotFound, the error is
 //     propagated (fail-fast: a prefixed product type must have a corresponding saga).
 //  2. Otherwise, fall back to the static default WithdrawalScript.
 func (o *WithdrawalOrchestrator) resolveWithdrawalScript(ctx context.Context, account domain.CurrentAccount) (string, error) {
@@ -306,25 +306,25 @@ func (o *WithdrawalOrchestrator) resolveWithdrawalScript(ctx context.Context, ac
 
 	tenantID, ok := tenant.FromContext(ctx)
 	if !ok {
-		// No tenant context — fall back to static script
+		// No tenant context - fall back to static script
 		return o.withdrawalScript, nil
 	}
 
 	def, err := o.sagaResolver.ResolveForProductType(ctx, tenantID, account.ProductTypeCode(), "withdrawal")
 	if err != nil {
 		if errors.Is(err, refsaga.ErrSagaNotFound) {
-			// Prefix is defined but no saga found — fail fast per PRD convention
+			// Prefix is defined but no saga found - fail fast per PRD convention
 			return "", err
 		}
-		// ErrNotFound (product type or generic saga missing) — fall back to static script
+		// ErrNotFound (product type or generic saga missing) - fall back to static script
 		o.logger.Warn("saga resolution fell through to default withdrawal script",
 			"product_type_code", account.ProductTypeCode(),
 			"error", err)
 		return o.withdrawalScript, nil
 	}
 
-	if def.ResolvedScript == "" {
-		// Definition has no resolved script — fall back to static script
+	if def.Script == "" {
+		// Definition has no script - fall back to static script
 		o.logger.Warn("resolved saga definition has no script, using default",
 			"saga_name", def.Name,
 			"product_type_code", account.ProductTypeCode())
@@ -334,5 +334,5 @@ func (o *WithdrawalOrchestrator) resolveWithdrawalScript(ctx context.Context, ac
 	o.logger.Debug("using product-type-specific withdrawal saga",
 		"saga_name", def.Name,
 		"product_type_code", account.ProductTypeCode())
-	return def.ResolvedScript, nil
+	return def.Script, nil
 }

services/reference-data/migrations/20260406000001_remove_platform_ref.sql

@@ -0,0 +1,15 @@
+-- Remove platform_ref inheritance infrastructure
+
+-- Backfill any NULL scripts before adding NOT NULL constraint.
+-- platform_ref sagas that were never backfilled get a placeholder so the
+-- migration does not fail. In practice all rows already have scripts
+-- (seeder copies content directly), but this guards against edge cases.
+UPDATE saga_definition SET script = '' WHERE script IS NULL;
+
+ALTER TABLE saga_definition DROP CONSTRAINT IF EXISTS chk_saga_definition_script_source;
+ALTER TABLE saga_definition DROP CONSTRAINT IF EXISTS fk_saga_definition_platform_ref;
+DROP INDEX IF EXISTS idx_saga_definition_platform_ref;
+ALTER TABLE saga_definition DROP COLUMN IF EXISTS platform_ref;
+ALTER TABLE saga_definition DROP COLUMN IF EXISTS override_reason;
+ALTER TABLE saga_definition DROP COLUMN IF EXISTS platform_version_at_override;
+ALTER TABLE saga_definition ALTER COLUMN script SET NOT NULL;

services/reference-data/migrations/atlas.sum

@@ -1,4 +1,4 @@
-h1:EwBq+L017EYbTiGH2/bdEcRZzy3RR8fK/INabZpg6bw=
+h1:kgCY6RqEoKl5lYUcivK1Zy3sGgb0sjOcDwxaK2r5t44=
 20260104000001_initial.sql h1:2h8BgK7z85efnTzrKZ23RRN3HPtRf9UOTy9FXhA33ik=
 20260105000001_add_is_system.sql h1:eRDijg0+SC31BlTqSxDUO/5651nNGlvfHCRhP2W1xlk=
 20260106000001_add_successor_id.sql h1:QasQ5t/OPJ8j138LFpSwy38qGwTyKWwWSlVg1EsPifc=
@@ -25,3 +25,4 @@ h1:EwBq+L017EYbTiGH2/bdEcRZzy3RR8fK/INabZpg6bw=
 20260221000002_mapping_definition_active_index.sql h1:I9S39ww++QM08RZfgV57LWoV+1iaNU4DoHP8oO/Yhm4=
 20260227000001_add_carbon_data_dimensions.sql h1:X8NuEfGkfnseEzqWHw6kQwVkoemxYuKPCqLD2mGIh+4=
 20260227000002_add_carbon_data_dimensions_constraint.sql h1:D5DK06dglc7zJBJWtWQfb83mVPEUmFZOq0z1bqenb3M=
+20260406000001_remove_platform_ref.sql h1:jlk8Tljyi49mk+e8s2gzkK2DNP5GciCFnH+hxlclhrQ=