Fix allocation-size overflow risk in model pricing merge (#43468)

* Initial plan

* Fix model pricing overflow regression

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: Peli de Halleux <pelikhan@users.noreply.github.com>

Author: Copilot

pkg/workflow/compiler_model_pricing.go

@@ -162,9 +162,9 @@ func mergeModelPricingIntoModelCosts(modelCosts map[string]any, provider, model
 	}
 	modelEntry := map[string]any{"cost": cost}
 
-	// Shallow-clone the top-level map. Do not add +1 here to avoid potential
-	// integer overflow; Go maps grow automatically as entries are added.
-	result := make(map[string]any, len(modelCosts))
+	// Shallow-clone the top-level map without pre-sizing to avoid reintroducing
+	// allocation-size arithmetic in this security-sensitive path.
+	result := make(map[string]any)
 	maps.Copy(result, modelCosts)
 
 	// Shallow-clone the providers map.

pkg/workflow/compiler_model_pricing_test.go

@@ -4,6 +4,11 @@ package workflow
 
 import (
 	"context"
+	"go/ast"
+	"go/parser"
+	gotoken "go/token"
+	"path/filepath"
+	"runtime"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -85,6 +90,49 @@ func TestMergeModelPricingIntoModelCosts_DoesNotMutateInput(t *testing.T) {
 	assert.Empty(t, openai["models"].(map[string]any))
 }
 
+func TestMergeModelPricingIntoModelCosts_DoesNotPreSizeTopLevelClone(t *testing.T) {
+	_, thisFile, _, ok := runtime.Caller(0)
+	require.True(t, ok, "runtime.Caller failed")
+
+	sourcePath := filepath.Join(filepath.Dir(thisFile), "compiler_model_pricing.go")
+	file, err := parser.ParseFile(gotoken.NewFileSet(), sourcePath, nil, parser.SkipObjectResolution)
+	require.NoError(t, err)
+
+	var foundResultMake bool
+	ast.Inspect(file, func(n ast.Node) bool {
+		fn, ok := n.(*ast.FuncDecl)
+		if !ok || fn.Name.Name != "mergeModelPricingIntoModelCosts" {
+			return true
+		}
+
+		for _, stmt := range fn.Body.List {
+			assign, ok := stmt.(*ast.AssignStmt)
+			if !ok || len(assign.Lhs) != 1 || len(assign.Rhs) != 1 {
+				continue
+			}
+			lhs, ok := assign.Lhs[0].(*ast.Ident)
+			if !ok || lhs.Name != "result" {
+				continue
+			}
+			call, ok := assign.Rhs[0].(*ast.CallExpr)
+			if !ok {
+				continue
+			}
+			fun, ok := call.Fun.(*ast.Ident)
+			if !ok || fun.Name != "make" {
+				continue
+			}
+
+			foundResultMake = true
+			assert.Len(t, call.Args, 1, "result map allocation should not pre-size capacity")
+			return false
+		}
+		return false
+	})
+
+	assert.True(t, foundResultMake, "expected to find result map allocation in mergeModelPricingIntoModelCosts")
+}
+
 // ── resolveEngineProviderForPricing ─────────────────────────────────────────
 
 func TestResolveEngineProviderForPricing(t *testing.T) {