Don't serialize the frozen field

build.zig

@@ -140,7 +140,7 @@ pub fn build(b: *std.Build) void {
             .name = "builtin_compiler",
             .root_source_file = b.path("src/build/builtin_compiler/main.zig"),
             .target = b.graph.host, // this runs at build time on the *host* machine!
-            .optimize = .ReleaseFast, // Must match playground optimization to ensure struct compatibility
+            .optimize = .Debug, // No need to optimize - only compiles builtin modules
             // Note: libc linking is handled by add_tracy below (required when tracy is enabled)
         });
 
@@ -234,7 +234,7 @@ pub fn build(b: *std.Build) void {
         .name = "builtin_compiler",
         .root_source_file = b.path("src/build/builtin_compiler/main.zig"),
         .target = b.graph.host,
-        .optimize = .ReleaseFast, // Must match playground optimization to ensure struct compatibility
+        .optimize = .Debug,
     });
 
     builtin_compiler_exe_force.root_module.addImport("base", roc_modules.base);

src/base/SmallStringInterner.zig

@@ -223,7 +223,6 @@ pub const Serialized = struct {
     bytes: collections.SafeList(u8).Serialized,
     hash_table: collections.SafeList(Idx).Serialized,
     entry_count: u32,
-    frozen: if (std.debug.runtime_safety) bool else void,
 
     /// Serialize a SmallStringInterner into this Serialized struct, appending data to the writer
     pub fn serialize(
@@ -238,7 +237,7 @@ pub const Serialized = struct {
         try self.hash_table.serialize(&interner.hash_table, allocator, writer);
         // Copy simple values directly
         self.entry_count = interner.entry_count;
-        self.frozen = interner.frozen;
+        // Note: frozen is not serialized - it will always be true after deserialization
     }
 
     /// Deserialize this Serialized struct into a SmallStringInterner
@@ -253,7 +252,7 @@ pub const Serialized = struct {
             .bytes = self.bytes.deserialize(offset).*,
             .hash_table = self.hash_table.deserialize(offset).*,
             .entry_count = self.entry_count,
-            .frozen = self.frozen,
+            .frozen = if (std.debug.runtime_safety) true else {}, // Always frozen after deserialization
         };
 
         return interner;

src/base/StringLiteral.zig

@@ -115,7 +115,6 @@ pub const Store = struct {
     /// Serialized representation of a Store
     pub const Serialized = struct {
         buffer: collections.SafeList(u8).Serialized,
-        frozen: if (std.debug.runtime_safety) bool else void,
 
         /// Serialize a Store into this Serialized struct, appending data to the writer
         pub fn serialize(
@@ -126,8 +125,7 @@ pub const Store = struct {
         ) std.mem.Allocator.Error!void {
             // Serialize the buffer SafeList
             try self.buffer.serialize(&store.buffer, allocator, writer);
-            // Copy the frozen field
-            self.frozen = store.frozen;
+            // Note: frozen is not serialized - it will always be true after deserialization
         }
 
         /// Deserialize this Serialized struct into a Store
@@ -140,7 +138,7 @@ pub const Store = struct {
 
             store.* = Store{
                 .buffer = self.buffer.deserialize(offset).*,
-                .frozen = self.frozen,
+                .frozen = if (std.debug.runtime_safety) true else {}, // Always frozen after deserialization
             };
 
             return store;