diff --git a/internal/runtime/executor/claude_builtin_tools_test.go b/internal/runtime/executor/claude_builtin_tools_test.go
deleted file mode 100644
index 34036fa0..00000000
--- a/internal/runtime/executor/claude_builtin_tools_test.go
+++ /dev/null
@@ -1,46 +0,0 @@
-package executor
-
-import (
-	"fmt"
-	"testing"
-
-	"github.com/tidwall/gjson"
-)
-
-func TestClaudeBuiltinToolRegistry_DefaultSeedFallback(t *testing.T) {
-	registry := augmentClaudeBuiltinToolRegistry(nil, nil)
-	for _, name := range defaultClaudeBuiltinToolNames {
-		if !registry[name] {
-			t.Fatalf("default builtin %q missing from fallback registry", name)
-		}
-	}
-}
-
-func TestApplyClaudeToolPrefix_KnownFallbackBuiltinsRemainUnprefixed(t *testing.T) {
-	for _, builtin := range defaultClaudeBuiltinToolNames {
-		t.Run(builtin, func(t *testing.T) {
-			input := []byte(fmt.Sprintf(`{
-				"tools":[{"name":"Read"}],
-				"tool_choice":{"type":"tool","name":%q},
-				"messages":[{"role":"assistant","content":[{"type":"tool_use","name":%q,"id":"toolu_1","input":{}},{"type":"tool_reference","tool_name":%q},{"type":"tool_result","tool_use_id":"toolu_1","content":[{"type":"tool_reference","tool_name":%q}]}]}]
-			}`, builtin, builtin, builtin, builtin))
-			out := applyClaudeToolPrefix(input, "proxy_")
-
-			if got := gjson.GetBytes(out, "tool_choice.name").String(); got != builtin {
-				t.Fatalf("tool_choice.name = %q, want %q", got, builtin)
-			}
-			if got := gjson.GetBytes(out, "messages.0.content.0.name").String(); got != builtin {
-				t.Fatalf("messages.0.content.0.name = %q, want %q", got, builtin)
-			}
-			if got := gjson.GetBytes(out, "messages.0.content.1.tool_name").String(); got != builtin {
-				t.Fatalf("messages.0.content.1.tool_name = %q, want %q", got, builtin)
-			}
-			if got := gjson.GetBytes(out, "messages.0.content.2.content.0.tool_name").String(); got != builtin {
-				t.Fatalf("messages.0.content.2.content.0.tool_name = %q, want %q", got, builtin)
-			}
-			if got := gjson.GetBytes(out, "tools.0.name").String(); got != "proxy_Read" {
-				t.Fatalf("tools.0.name = %q, want %q", got, "proxy_Read")
-			}
-		})
-	}
-}
diff --git a/internal/runtime/executor/claude_executor.go b/internal/runtime/executor/claude_executor.go
index d1d2e136..120b1f35 100644
--- a/internal/runtime/executor/claude_executor.go
+++ b/internal/runtime/executor/claude_executor.go
@@ -921,7 +921,7 @@ func applyClaudeToolPrefix(body []byte, prefix string) []byte {
 
 	// Collect built-in tool names from the authoritative fallback seed list and
 	// augment it with any typed built-ins present in the current request body.
-	builtinTools := augmentClaudeBuiltinToolRegistry(body, nil)
+	builtinTools := helps.AugmentClaudeBuiltinToolRegistry(body, nil)
 
 	if tools := gjson.GetBytes(body, "tools"); tools.Exists() && tools.IsArray() {
 		tools.ForEach(func(index, tool gjson.Result) bool {
diff --git a/internal/runtime/executor/claude_executor_test.go b/internal/runtime/executor/claude_executor_test.go
index 8e8173dd..e5f907b7 100644
--- a/internal/runtime/executor/claude_executor_test.go
+++ b/internal/runtime/executor/claude_executor_test.go
@@ -739,6 +739,35 @@ func TestApplyClaudeToolPrefix_ToolChoiceBuiltin(t *testing.T) {
 	}
 }
 
+func TestApplyClaudeToolPrefix_KnownFallbackBuiltinsRemainUnprefixed(t *testing.T) {
+	for _, builtin := range []string{"web_search", "code_execution", "text_editor", "computer"} {
+		t.Run(builtin, func(t *testing.T) {
+			input := []byte(fmt.Sprintf(`{
+				"tools":[{"name":"Read"}],
+				"tool_choice":{"type":"tool","name":%q},
+				"messages":[{"role":"assistant","content":[{"type":"tool_use","name":%q,"id":"toolu_1","input":{}},{"type":"tool_reference","tool_name":%q},{"type":"tool_result","tool_use_id":"toolu_1","content":[{"type":"tool_reference","tool_name":%q}]}]}]
+			}`, builtin, builtin, builtin, builtin))
+			out := applyClaudeToolPrefix(input, "proxy_")
+
+			if got := gjson.GetBytes(out, "tool_choice.name").String(); got != builtin {
+				t.Fatalf("tool_choice.name = %q, want %q", got, builtin)
+			}
+			if got := gjson.GetBytes(out, "messages.0.content.0.name").String(); got != builtin {
+				t.Fatalf("messages.0.content.0.name = %q, want %q", got, builtin)
+			}
+			if got := gjson.GetBytes(out, "messages.0.content.1.tool_name").String(); got != builtin {
+				t.Fatalf("messages.0.content.1.tool_name = %q, want %q", got, builtin)
+			}
+			if got := gjson.GetBytes(out, "messages.0.content.2.content.0.tool_name").String(); got != builtin {
+				t.Fatalf("messages.0.content.2.content.0.tool_name = %q, want %q", got, builtin)
+			}
+			if got := gjson.GetBytes(out, "tools.0.name").String(); got != "proxy_Read" {
+				t.Fatalf("tools.0.name = %q, want %q", got, "proxy_Read")
+			}
+		})
+	}
+}
+
 func TestStripClaudeToolPrefixFromResponse(t *testing.T) {
 	input := []byte(`{"content":[{"type":"tool_use","name":"proxy_alpha","id":"t1","input":{}},{"type":"tool_use","name":"bravo","id":"t2","input":{}}]}`)
 	out := stripClaudeToolPrefixFromResponse(input, "proxy_")
diff --git a/internal/runtime/executor/claude_builtin_tools.go b/internal/runtime/executor/helps/claude_builtin_tools.go
similarity index 90%
rename from internal/runtime/executor/claude_builtin_tools.go
rename to internal/runtime/executor/helps/claude_builtin_tools.go
index 8c3592f7..5ee2b08d 100644
--- a/internal/runtime/executor/claude_builtin_tools.go
+++ b/internal/runtime/executor/helps/claude_builtin_tools.go
@@ -1,4 +1,4 @@
-package executor
+package helps
 
 import "github.com/tidwall/gjson"
 
@@ -17,7 +17,7 @@ func newClaudeBuiltinToolRegistry() map[string]bool {
 	return registry
 }
 
-func augmentClaudeBuiltinToolRegistry(body []byte, registry map[string]bool) map[string]bool {
+func AugmentClaudeBuiltinToolRegistry(body []byte, registry map[string]bool) map[string]bool {
 	if registry == nil {
 		registry = newClaudeBuiltinToolRegistry()
 	}
diff --git a/internal/runtime/executor/helps/claude_builtin_tools_test.go b/internal/runtime/executor/helps/claude_builtin_tools_test.go
new file mode 100644
index 00000000..d7badd19
--- /dev/null
+++ b/internal/runtime/executor/helps/claude_builtin_tools_test.go
@@ -0,0 +1,32 @@
+package helps
+
+import "testing"
+
+func TestClaudeBuiltinToolRegistry_DefaultSeedFallback(t *testing.T) {
+	registry := AugmentClaudeBuiltinToolRegistry(nil, nil)
+	for _, name := range defaultClaudeBuiltinToolNames {
+		if !registry[name] {
+			t.Fatalf("default builtin %q missing from fallback registry", name)
+		}
+	}
+}
+
+func TestClaudeBuiltinToolRegistry_AugmentsTypedBuiltinsFromBody(t *testing.T) {
+	registry := AugmentClaudeBuiltinToolRegistry([]byte(`{
+		"tools": [
+			{"type": "web_search_20250305", "name": "web_search"},
+			{"type": "custom_builtin_20250401", "name": "special_builtin"},
+			{"name": "Read"}
+		]
+	}`), nil)
+
+	if !registry["web_search"] {
+		t.Fatal("expected default typed builtin web_search in registry")
+	}
+	if !registry["special_builtin"] {
+		t.Fatal("expected typed builtin from body to be added to registry")
+	}
+	if registry["Read"] {
+		t.Fatal("expected untyped custom tool to stay out of builtin registry")
+	}
+}