diff --git a/packages/cli/test/native-link-info.test.ts b/packages/cli/test/native-link-info.test.ts
index a7a5e718a..a1b673630 100644
--- a/packages/cli/test/native-link-info.test.ts
+++ b/packages/cli/test/native-link-info.test.ts
@@ -72,7 +72,7 @@ describe.runIf(supported)("macOS arm64 native link info", () => {
         minimum_os: "14.0",
       },
       program: { object, entry_symbol: "main" },
-      runtime_abi: { version: 27, marker: "scr_runtime_abi_v27" },
+      runtime_abi: { version: 28, marker: "scr_runtime_abi_v28" },
       runtime_pack: {
         kind: "precompiled",
         package: "@scriptc/runtime-darwin-arm64",
@@ -165,6 +165,6 @@ describe.runIf(supported)("macOS arm64 native link info", () => {
       () => null,
       (failure: { stderr?: string }) => failure,
     );
-    expect(error?.stderr).toContain("scr_runtime_abi_v27");
+    expect(error?.stderr).toContain("scr_runtime_abi_v28");
   });
 });
diff --git a/packages/compiler/src/backend/llvm/emit-module.ts b/packages/compiler/src/backend/llvm/emit-module.ts
index 3d9d41072..47d92e3bd 100644
--- a/packages/compiler/src/backend/llvm/emit-module.ts
+++ b/packages/compiler/src/backend/llvm/emit-module.ts
@@ -727,6 +727,8 @@ export function emitModuleParts(emitter: LlEmitter): string[] {
     out.push(`@${sym} = internal constant { ptr, ptr, ptr, ptr, ptr, ptr, ptr } { ${body} }`);
   }
   if (emitter.mapOpsConsts.size > 0) out.push(``);
+  for (const sym of emitter.methodIdSlots.values()) out.push(`@${sym} = internal global i32 -1`);
+  if (emitter.methodIdSlots.size > 0) out.push(``);
 
   for (const line of ffiCallbacks.globals) out.push(line);
   if (ffiCallbacks.globals.length > 0) out.push(``);
diff --git a/packages/compiler/src/backend/llvm/emitter.ts b/packages/compiler/src/backend/llvm/emitter.ts
index bfde59a30..ee8e69e94 100644
--- a/packages/compiler/src/backend/llvm/emitter.ts
+++ b/packages/compiler/src/backend/llvm/emitter.ts
@@ -782,6 +782,10 @@ export class LlEmitter {
   readonly cstrs = new Map<string, { sym: string; len: number }>();
   /** Interned ScrMapOps descriptors (scr_map.h): initializer → symbol. */
   readonly mapOpsConsts = new Map<string, string>();
+  /** Method-id slots of checked-dynamic method calls
+   * (scr_dyn_invoke_prepared_id): method name → symbol of an i32 the
+   * runtime fills with the name's id on the first call. */
+  readonly methodIdSlots = new Map<string, string>();
   /** Type-directed walker functions (JSON serializers, the indent
    * rewriter, union ToString/join) — interned per typeKey/unionId, defs
    * flushed with the shape helpers. */
@@ -2400,6 +2404,16 @@ export class LlEmitter {
     return `@${c.sym}`;
   }
 
+  /** The method-id slot for a constant method name (methodIdSlots). */
+  methodIdSlot(name: string): string {
+    let sym = this.methodIdSlots.get(name);
+    if (!sym) {
+      sym = this.contentSymbol("sc_mid_", name);
+      this.methodIdSlots.set(name, sym);
+    }
+    return `@${sym}`;
+  }
+
   needBadTag(): void {
     this.needsBadTag = true;
   }
diff --git a/packages/compiler/src/backend/llvm/expr-dynamic.ts b/packages/compiler/src/backend/llvm/expr-dynamic.ts
index 58bb90569..e3d0dc8f2 100644
--- a/packages/compiler/src/backend/llvm/expr-dynamic.ts
+++ b/packages/compiler/src/backend/llvm/expr-dynamic.ts
@@ -250,8 +250,10 @@ export function emitDynamicExpr(
       }
       // Buffer.prototype method names take their scr_bytes_dyn.c entry, which
       // runs them on Buffer receivers and dispatches any other receiver.
-      const invoke = DYN_BUFFER_METHODS.get(e.method) ?? "scr_dyn_invoke_prepared";
-      host.declare(`declare ptr @${invoke}(ptr, ptr, ptr, ptr, ${host.sizeType}, ptr)`);
+      // Each call passes its method name's id slot, so only the first call
+      // looks the name up.
+      const invoke = DYN_BUFFER_METHODS.get(e.method) ?? "scr_dyn_invoke_prepared_id";
+      host.declare(`declare ptr @${invoke}(ptr, ptr, ptr, ptr, ptr, ${host.sizeType}, ptr)`);
       let name = host.cstr(e.calleeName);
       if (e.calleeNameValue !== undefined) {
         const value = emitBorrowedInput(host, e.calleeNameValue);
@@ -260,7 +262,7 @@ export function emitDynamicExpr(
       }
       const t = B.tmp();
       B.line(
-        `${t} = call ptr @${invoke}(ptr ${recv.name}, ptr ${prepared}, ptr ${host.cstr(e.method)}, ptr ${argsPtr}, ${host.sizeType} ${args.length}, ptr ${name})`,
+        `${t} = call ptr @${invoke}(ptr ${recv.name}, ptr ${prepared}, ptr ${host.cstr(e.method)}, ptr ${host.methodIdSlot(e.method)}, ptr ${argsPtr}, ${host.sizeType} ${args.length}, ptr ${name})`,
       );
       const out = host.own({ name: t, type: e.type });
       host.emitPendingCheck();
diff --git a/packages/compiler/src/backend/llvm/js-ic.ts b/packages/compiler/src/backend/llvm/js-ic.ts
index 45c18b803..7516673cd 100644
--- a/packages/compiler/src/backend/llvm/js-ic.ts
+++ b/packages/compiler/src/backend/llvm/js-ic.ts
@@ -732,7 +732,7 @@ function emitKeyed(host: Host, e: ExprOf<"call">, callee: IrFunction): LlValue {
 
 /** dynInvoke's method read on an ordinary object through the site's
  * cache, else scr_dyn_prepare_method. Returns the owned method (or NULL,
- * which scr_dyn_invoke_prepared answers with the full dispatch). */
+ * which scr_dyn_invoke_prepared_id answers with the full dispatch). */
 export function emitJsIcMethod(host: Host, e: ExprOf<"dynInvoke">, receiver: string): string {
   const B = host.B;
   const method = e.method;
diff --git a/packages/compiler/src/backend/runtime-abi.ts b/packages/compiler/src/backend/runtime-abi.ts
index 3a41d9176..a616dbec2 100644
--- a/packages/compiler/src/backend/runtime-abi.ts
+++ b/packages/compiler/src/backend/runtime-abi.ts
@@ -2,8 +2,8 @@
  * of the link contract: a program object keeps this symbol undefined and the
  * matching runtime defines it, so incompatible manual links fail before the
  * program can start. */
-export const RUNTIME_ABI_VERSION = 27 as const;
-export const RUNTIME_ABI_MARKER = "scr_runtime_abi_v27" as const;
+export const RUNTIME_ABI_VERSION = 28 as const;
+export const RUNTIME_ABI_MARKER = "scr_runtime_abi_v28" as const;
 
 /** Object consumption is useful today, but the complete scr_* surface may
  * still change before 1.0. The versioned marker prevents accidental mixing;
diff --git a/packages/compiler/src/backend/runtime-pack-targets.test.ts b/packages/compiler/src/backend/runtime-pack-targets.test.ts
index af61e5229..c2536ede8 100644
--- a/packages/compiler/src/backend/runtime-pack-targets.test.ts
+++ b/packages/compiler/src/backend/runtime-pack-targets.test.ts
@@ -52,7 +52,7 @@ async function fixture(target: NativeTargetSpec, workers = false) {
       object_format: target.objectFormat,
       minimum_os: target.minimumOs,
     },
-    runtime_abi: { version: 27, marker: "scr_runtime_abi_v27" },
+    runtime_abi: { version: 28, marker: "scr_runtime_abi_v28" },
     compiler: { command: "fixture", identity: "fixture", target: target.llvmTriple },
     macros: { executable: [], excluded: ["SCR_LIB"], sanitizer: "external-toolchain-required" },
     flavors: {
diff --git a/packages/compiler/src/backend/runtime-pack.test.ts b/packages/compiler/src/backend/runtime-pack.test.ts
index d09509911..33b1ca38e 100644
--- a/packages/compiler/src/backend/runtime-pack.test.ts
+++ b/packages/compiler/src/backend/runtime-pack.test.ts
@@ -127,7 +127,7 @@ async function fixture(target: NativeTargetSpec = MACOS_ARM64_TARGET) {
       object_format: target.objectFormat,
       minimum_os: target.minimumOs,
     },
-    runtime_abi: { version: 27, marker: "scr_runtime_abi_v27" },
+    runtime_abi: { version: 28, marker: "scr_runtime_abi_v28" },
     compiler: {
       command: "clang",
       identity: "fixture clang",
diff --git a/packages/compiler/test/native-codegen-integration.test.ts b/packages/compiler/test/native-codegen-integration.test.ts
index 35a747d60..71b9570b4 100644
--- a/packages/compiler/test/native-codegen-integration.test.ts
+++ b/packages/compiler/test/native-codegen-integration.test.ts
@@ -378,7 +378,7 @@ done:
     expect(await symbols(helperObject, ["-u"])).toEqual(await symbols(clangObject, ["-u"]));
     expect(await symbols(helperObject, ["-gU"])).toEqual(await symbols(clangObject, ["-gU"]));
     expect(await symbols(helperObject, ["-gU"])).toEqual(["0000000000000000 T _main"]);
-    expect(await symbols(helperObject, ["-u"])).toContain("_scr_runtime_abi_v27");
+    expect(await symbols(helperObject, ["-u"])).toContain("_scr_runtime_abi_v28");
 
     const clangExe = join(dir, "clang-program");
     const linkDriver = join(dir, "clang-driver.c");
@@ -712,7 +712,7 @@ done:
       .split("\n");
     expect(undefinedSymbols).toContain("_sf_scale");
     expect(undefinedSymbols).toContain("_sf_callback_mix");
-    expect(undefinedSymbols).toContain("_scr_runtime_abi_v27");
+    expect(undefinedSymbols).toContain("_scr_runtime_abi_v28");
   });
 
   test("helper and clang object paths retain the same outbound FFI C ABI", async () => {
diff --git a/packages/runtime-darwin-arm64/scripts/build.mjs b/packages/runtime-darwin-arm64/scripts/build.mjs
index 631750cdf..3d22b2360 100644
--- a/packages/runtime-darwin-arm64/scripts/build.mjs
+++ b/packages/runtime-darwin-arm64/scripts/build.mjs
@@ -340,7 +340,7 @@ async function build() {
       package: packageManifest.name,
       version: packageManifest.version,
       target: RUNTIME_PACK_MATRIX.target,
-      runtime_abi: { version: 27, marker: "scr_runtime_abi_v27" },
+      runtime_abi: { version: 28, marker: "scr_runtime_abi_v28" },
       compiler: {
         command: compiler,
         identity: compilerVersion,
diff --git a/packages/runtime-pack-common/scripts/build.mjs b/packages/runtime-pack-common/scripts/build.mjs
index 0e81033ad..909412bc7 100644
--- a/packages/runtime-pack-common/scripts/build.mjs
+++ b/packages/runtime-pack-common/scripts/build.mjs
@@ -437,7 +437,7 @@ async function build() {
       package: packageManifest.name,
       version: packageManifest.version,
       target: matrix.target,
-      runtime_abi: { version: 27, marker: "scr_runtime_abi_v27" },
+      runtime_abi: { version: 28, marker: "scr_runtime_abi_v28" },
       compiler: {
         command: compiler,
         identity: compilerVersion,
diff --git a/packages/runtime/src/scr_bytes_dyn.c b/packages/runtime/src/scr_bytes_dyn.c
index 280aa423c..c492d43b1 100644
--- a/packages/runtime/src/scr_bytes_dyn.c
+++ b/packages/runtime/src/scr_bytes_dyn.c
@@ -509,8 +509,9 @@ static bool scr_bytes_dyn_buffer(const ScrDyn *recv) {
 /* One entry per method family, so a program links only the families it
  * names: each runs its methods on a Buffer receiver and gives any other
  * receiver the ordinary dispatch. */
-ScrDyn *scr_dyn_invoke_buffer_num(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args,
-                                  size_t argc, const char *what) {
+ScrDyn *scr_dyn_invoke_buffer_num(ScrDyn *recv, ScrDyn *callee, const char *method,
+                                  int32_t *mid_slot, ScrDyn *const *args, size_t argc,
+                                  const char *what) {
   if (scr_bytes_dyn_buffer(recv)) {
     bool read = !strncmp(method, "read", 4);
     const char *rest = method + (read ? 4 : 5);
@@ -518,40 +519,45 @@ ScrDyn *scr_dyn_invoke_buffer_num(ScrDyn *recv, ScrDyn *callee, const char *meth
       if (!strcmp(rest, scr_bytes_dyn_names[at].name)) return scr_bytes_dyn_num_method(recv->v.bytes, read, at, args, argc);
     }
   }
-  return scr_dyn_invoke_prepared(recv, callee, method, args, argc, what);
+  return scr_dyn_invoke_prepared_id(recv, callee, method, mid_slot, args, argc, what);
 }
 
-ScrDyn *scr_dyn_invoke_buffer_write(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args,
-                                    size_t argc, const char *what) {
+ScrDyn *scr_dyn_invoke_buffer_write(ScrDyn *recv, ScrDyn *callee, const char *method,
+                                    int32_t *mid_slot, ScrDyn *const *args, size_t argc,
+                                    const char *what) {
   if (scr_bytes_dyn_buffer(recv)) return scr_bytes_dyn_write(recv->v.bytes, args, argc);
-  return scr_dyn_invoke_prepared(recv, callee, method, args, argc, what);
+  return scr_dyn_invoke_prepared_id(recv, callee, method, mid_slot, args, argc, what);
 }
 
-ScrDyn *scr_dyn_invoke_buffer_fill(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args,
-                                   size_t argc, const char *what) {
+ScrDyn *scr_dyn_invoke_buffer_fill(ScrDyn *recv, ScrDyn *callee, const char *method,
+                                   int32_t *mid_slot, ScrDyn *const *args, size_t argc,
+                                   const char *what) {
   if (scr_bytes_dyn_buffer(recv)) return scr_bytes_dyn_fill(recv, args, argc);
-  return scr_dyn_invoke_prepared(recv, callee, method, args, argc, what);
+  return scr_dyn_invoke_prepared_id(recv, callee, method, mid_slot, args, argc, what);
 }
 
-ScrDyn *scr_dyn_invoke_buffer_to_string(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args,
-                                        size_t argc, const char *what) {
+ScrDyn *scr_dyn_invoke_buffer_to_string(ScrDyn *recv, ScrDyn *callee, const char *method,
+                                        int32_t *mid_slot, ScrDyn *const *args, size_t argc,
+                                        const char *what) {
   if (scr_bytes_dyn_buffer(recv)) return scr_bytes_dyn_to_string(recv->v.bytes, args, argc);
-  return scr_dyn_invoke_prepared(recv, callee, method, args, argc, what);
+  return scr_dyn_invoke_prepared_id(recv, callee, method, mid_slot, args, argc, what);
 }
 
 /* indexOf, lastIndexOf and includes. */
-ScrDyn *scr_dyn_invoke_buffer_search(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args,
-                                     size_t argc, const char *what) {
+ScrDyn *scr_dyn_invoke_buffer_search(ScrDyn *recv, ScrDyn *callee, const char *method,
+                                     int32_t *mid_slot, ScrDyn *const *args, size_t argc,
+                                     const char *what) {
   if (scr_bytes_dyn_buffer(recv)) {
     bool includes = !strcmp(method, "includes");
     return scr_bytes_dyn_index_of(recv->v.bytes, args, argc, strcmp(method, "lastIndexOf") != 0, includes);
   }
-  return scr_dyn_invoke_prepared(recv, callee, method, args, argc, what);
+  return scr_dyn_invoke_prepared_id(recv, callee, method, mid_slot, args, argc, what);
 }
 
 /* toJSON, equals, compare, copy, swap16/32/64, and the refused members. */
-ScrDyn *scr_dyn_invoke_buffer(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args,
-                              size_t argc, const char *what) {
+ScrDyn *scr_dyn_invoke_buffer(ScrDyn *recv, ScrDyn *callee, const char *method,
+                              int32_t *mid_slot, ScrDyn *const *args, size_t argc,
+                              const char *what) {
   if (scr_bytes_dyn_buffer(recv)) {
     ScrBytes *b = recv->v.bytes;
     if (!strcmp(method, "toJSON")) return scr_bytes_dyn_to_json(b);
@@ -584,5 +590,5 @@ ScrDyn *scr_dyn_invoke_buffer(ScrDyn *recv, ScrDyn *callee, const char *method,
       return NULL;
     }
   }
-  return scr_dyn_invoke_prepared(recv, callee, method, args, argc, what);
+  return scr_dyn_invoke_prepared_id(recv, callee, method, mid_slot, args, argc, what);
 }
diff --git a/packages/runtime/src/scr_console.c b/packages/runtime/src/scr_console.c
index a3ac43cc0..9bd5abf8c 100644
--- a/packages/runtime/src/scr_console.c
+++ b/packages/runtime/src/scr_console.c
@@ -148,7 +148,7 @@ static void scr_enable_utf8_console_output(void) {
 }
 #endif
 
-void scr_runtime_abi_v27(void) {}
+void scr_runtime_abi_v28(void) {}
 
 void scr_init(void) {
 #ifdef SCR_WORKERS
diff --git a/packages/runtime/src/scr_core.h b/packages/runtime/src/scr_core.h
index fea020d16..35332d0ca 100644
--- a/packages/runtime/src/scr_core.h
+++ b/packages/runtime/src/scr_core.h
@@ -81,7 +81,7 @@ void scr_init(void);
 /* Program objects emitted by the bundled LLVM helper reference this symbol.
  * Its versioned spelling makes a mismatched manual runtime link fail before
  * the program can start. */
-void scr_runtime_abi_v27(void);
+void scr_runtime_abi_v28(void);
 void scr_runtime_workers_v8(void);
 
 /* ── the trap funnel (scr_console.c; scr_library.c under -DSCR_LIB) ──────
diff --git a/packages/runtime/src/scr_dyn.h b/packages/runtime/src/scr_dyn.h
index bb3b06847..2bdf95562 100644
--- a/packages/runtime/src/scr_dyn.h
+++ b/packages/runtime/src/scr_dyn.h
@@ -1272,15 +1272,19 @@ bool scr_dyn_strict_eq(const ScrDyn *a, const ScrDyn *b);
  * result owned (+1). MAY THROW (NULL with the exception pending). */
 ScrDyn *scr_dyn_prepare_method(ScrDyn *recv, const char *method);
 ScrDyn *scr_dyn_invoke_prepared(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args, size_t argc, const char *what);
-/* scr_dyn_invoke_prepared for Buffer.prototype method names (scr_bytes_dyn.c),
- * one entry per method family: a Buffer receiver runs the method, any other
- * takes the ordinary dispatch. */
-ScrDyn *scr_dyn_invoke_buffer_num(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args, size_t argc, const char *what);
-ScrDyn *scr_dyn_invoke_buffer_write(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args, size_t argc, const char *what);
-ScrDyn *scr_dyn_invoke_buffer_fill(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args, size_t argc, const char *what);
-ScrDyn *scr_dyn_invoke_buffer_to_string(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args, size_t argc, const char *what);
-ScrDyn *scr_dyn_invoke_buffer_search(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args, size_t argc, const char *what);
-ScrDyn *scr_dyn_invoke_buffer(ScrDyn *recv, ScrDyn *callee, const char *method, ScrDyn *const *args, size_t argc, const char *what);
+/* scr_dyn_invoke_prepared for a call site whose method name is a constant:
+ * *mid_slot, the site's -1-initialized slot, caches the name's method id
+ * after the first call, so later calls skip the name lookup. */
+ScrDyn *scr_dyn_invoke_prepared_id(ScrDyn *recv, ScrDyn *callee, const char *method, int32_t *mid_slot, ScrDyn *const *args, size_t argc, const char *what);
+/* scr_dyn_invoke_prepared_id for Buffer.prototype method names
+ * (scr_bytes_dyn.c), one entry per method family: a Buffer receiver runs
+ * the method, any other takes the ordinary dispatch. */
+ScrDyn *scr_dyn_invoke_buffer_num(ScrDyn *recv, ScrDyn *callee, const char *method, int32_t *mid_slot, ScrDyn *const *args, size_t argc, const char *what);
+ScrDyn *scr_dyn_invoke_buffer_write(ScrDyn *recv, ScrDyn *callee, const char *method, int32_t *mid_slot, ScrDyn *const *args, size_t argc, const char *what);
+ScrDyn *scr_dyn_invoke_buffer_fill(ScrDyn *recv, ScrDyn *callee, const char *method, int32_t *mid_slot, ScrDyn *const *args, size_t argc, const char *what);
+ScrDyn *scr_dyn_invoke_buffer_to_string(ScrDyn *recv, ScrDyn *callee, const char *method, int32_t *mid_slot, ScrDyn *const *args, size_t argc, const char *what);
+ScrDyn *scr_dyn_invoke_buffer_search(ScrDyn *recv, ScrDyn *callee, const char *method, int32_t *mid_slot, ScrDyn *const *args, size_t argc, const char *what);
+ScrDyn *scr_dyn_invoke_buffer(ScrDyn *recv, ScrDyn *callee, const char *method, int32_t *mid_slot, ScrDyn *const *args, size_t argc, const char *what);
 ScrDyn *scr_dyn_invoke(ScrDyn *recv, const char *method, ScrDyn *const *args, size_t argc, const char *what);
 /* Keyed read on a FUNC node: the own-property table first (defineProperties
  * writes land there), then "name" (the box's best-effort static name; ""
diff --git a/packages/runtime/src/scr_dyn_invoke.c b/packages/runtime/src/scr_dyn_invoke.c
index b0f30ac74..d4189f070 100644
--- a/packages/runtime/src/scr_dyn_invoke.c
+++ b/packages/runtime/src/scr_dyn_invoke.c
@@ -724,7 +724,7 @@ static bool dyn_bytes_proto_real(int m) {
 }
 
 static ScrDyn *scr_dyn_invoke_impl(
-    ScrDyn *recv, const char *method, ScrDyn *const *args, size_t argc,
+    ScrDyn *recv, const char *method, int mid, ScrDyn *const *args, size_t argc,
     const char *what, ScrDyn *callback_recv);
 
 /* Live native arrays: the constant-time methods that loops call once per
@@ -796,13 +796,26 @@ ScrDyn *scr_dyn_invoke_prepared(ScrDyn *recv, ScrDyn *callee, const char *method
 ScrDyn *scr_dyn_invoke(ScrDyn *recv, const char *method,
                        ScrDyn *const *args, size_t argc,
                        const char *what) {
-  return scr_dyn_invoke_impl(recv, method, args, argc, what, NULL);
+  return scr_dyn_invoke_impl(recv, method, dyn_method_of(method), args, argc, what, NULL);
+}
+
+ScrDyn *scr_dyn_invoke_prepared_id(ScrDyn *recv, ScrDyn *callee, const char *method,
+                                  int32_t *mid_slot, ScrDyn *const *args, size_t argc,
+                                  const char *what) {
+  if (callee) return scr_dyn_invoke_prepared(recv, callee, method, args, argc, what);
+  /* The slot is the call site's, shared by every thread: each writes the
+   * same id. */
+  int32_t mid = __atomic_load_n(mid_slot, __ATOMIC_RELAXED);
+  if (mid < 0) {
+    mid = dyn_method_of(method);
+    __atomic_store_n(mid_slot, mid, __ATOMIC_RELAXED);
+  }
+  return scr_dyn_invoke_impl(recv, method, mid, args, argc, what, NULL);
 }
 
 static ScrDyn *scr_dyn_invoke_impl(
-    ScrDyn *recv, const char *method, ScrDyn *const *args, size_t argc,
+    ScrDyn *recv, const char *method, int mid, ScrDyn *const *args, size_t argc,
     const char *what, ScrDyn *callback_recv) {
-  const int mid = dyn_method_of(method);
   if (recv->kind == SCR_DYN_UNDEF || recv->kind == SCR_DYN_NULL) {
     ScrJsonBuf b;
     scr_jb_init(&b);
@@ -874,7 +887,7 @@ static ScrDyn *scr_dyn_invoke_impl(
     bool mutates = materialized->kind == SCR_DYN_ARR &&
                    dyn_arr_proto_mutates(mid);
     ScrDyn *result = scr_dyn_invoke_impl(
-        materialized, method, args, argc, what, recv);
+        materialized, method, mid, args, argc, what, recv);
     if (mutates && !scr_exc_pending()) scr_dyn_typed_ref_commit(recv);
     if (result == materialized) {
       scr_dyn_release(result);
diff --git a/tests/harness/self-hosting-native-toolchain.test.ts b/tests/harness/self-hosting-native-toolchain.test.ts
index c0176eb93..c4013d288 100644
--- a/tests/harness/self-hosting-native-toolchain.test.ts
+++ b/tests/harness/self-hosting-native-toolchain.test.ts
@@ -108,7 +108,7 @@ for (const backend of ["llvm"] as const) {
           object_format: target.objectFormat,
           minimum_os: target.minimumOs,
         },
-        runtime_abi: { version: 27, marker: "scr_runtime_abi_v27" },
+        runtime_abi: { version: 28, marker: "scr_runtime_abi_v28" },
         compiler: { command: "fixture", identity: "fixture", target: target.llvmTriple },
         macros: { executable: [], excluded: [], sanitizer: "external-toolchain-required" },
         flavors: {