diff --git a/src/script/command.zig b/src/script/command.zig
index e1fd44f9..05d51af2 100644
--- a/src/script/command.zig
+++ b/src/script/command.zig
@@ -284,16 +284,12 @@ fn formatToolCall(tc: Command.ToolCall, writer: *std.Io.Writer) std.Io.Writer.Er
     }
 }
 
-fn isDefaultTrueBool(s: *const schema.SchemaInfo, key: []const u8, v: std.json.Value) bool {
-    return v == .bool and v.bool and s.isFieldDefaultTrue(key);
-}
-
 /// Args that the recorder must NOT emit:
 ///   - `backendNodeId`: ephemeral identifier, never replayable.
 ///   - boolean fields whose value equals the schema default (cosmetic).
 fn skipForFormat(s: *const schema.SchemaInfo, key: []const u8, v: std.json.Value) bool {
     if (std.mem.eql(u8, key, "backendNodeId")) return true;
-    return isDefaultTrueBool(s, key, v);
+    return v == .bool and v.bool and s.isFieldDefaultTrue(key);
 }
 
 fn formatString(writer: *std.Io.Writer, s: []const u8) std.Io.Writer.Error!void {
diff --git a/src/script/schema.zig b/src/script/schema.zig
index 4a691e13..e8cb4f98 100644
--- a/src/script/schema.zig
+++ b/src/script/schema.zig
@@ -141,11 +141,15 @@ fn buildOne(arena: std.mem.Allocator, action: browser_tools.Action, td: browser_
 
 fn buildHints(arena: std.mem.Allocator, required: []const []const u8, fields: []const FieldEntry) ![]const HintSlot {
     if (fields.len == 0 and required.len == 0) return &.{};
-    // Worst case: every required name is absent from `properties`, so we emit
-    // one slot per required entry plus one per field. The returned slice is
-    // truncated to the actual count.
-    const out = try arena.alloc(HintSlot, required.len + fields.len);
+    var optional_count: usize = 0;
+    for (fields) |f| {
+        if (!containsName(required, f.name)) {
+            optional_count += 1;
+        }
+    }
+    const out = try arena.alloc(HintSlot, required.len + optional_count);
     var idx: usize = 0;
+    defer std.debug.assert(idx == out.len);
     for (required) |name| {
         out[idx] = .{
             .name = name,
@@ -163,7 +167,7 @@ fn buildHints(arena: std.mem.Allocator, required: []const []const u8, fields: []
         };
         idx += 1;
     }
-    return out[0..idx];
+    return out;
 }
 
 fn containsName(names: []const []const u8, target: []const u8) bool {