diff --git a/packages/compiler/src/frontend/lowering/lower-calls.ts b/packages/compiler/src/frontend/lowering/lower-calls.ts
index 766fb2976..5791e74a1 100644
--- a/packages/compiler/src/frontend/lowering/lower-calls.ts
+++ b/packages/compiler/src/frontend/lowering/lower-calls.ts
@@ -2684,7 +2684,7 @@ export function lowerFfiCall(L: Lowerer, expr: ts.CallExpression): IrExpr | null
       // No entry means the program-level pass already diagnosed this
       // binding. Poison the statement without duplicating that diagnostic.
       if (validSymbols === undefined) throw new PoisonError();
-      if (!validSymbols.has(symbol)) {
+      if (!L.ownsValidatedFfiSymbol(binding.name, symbol)) {
         // TypeScript resolved this call to a distinct local declaration.
         // The manifest owns only the exact validated ambient binding; a
         // same-named function with a body remains ordinary scriptc code.
diff --git a/packages/compiler/src/frontend/lowering/lower-namespaces.ts b/packages/compiler/src/frontend/lowering/lower-namespaces.ts
index 0ac9def7f..8ad09e7dd 100644
--- a/packages/compiler/src/frontend/lowering/lower-namespaces.ts
+++ b/packages/compiler/src/frontend/lowering/lower-namespaces.ts
@@ -340,37 +340,6 @@ export function ambientNsRootOf(L: Lowerer, e: ts.Expression): ts.Identifier | n
  * the order Node dies in. Null for stdlib/@types roots (their own
  * chokepoints stand) and anything declared with a value. */
 export function ambientUndefVarRootOf(L: Lowerer, e: ts.Expression): ts.Identifier | null {
-  let root: ts.Expression = e;
-  for (;;) {
-    if (
-      ts.isParenthesizedExpression(root) ||
-      ts.isNonNullExpression(root) ||
-      ts.isAsExpression(root) ||
-      ts.isSatisfiesExpression(root) ||
-      ts.isTypeAssertion(root)
-    ) {
-      root = root.expression;
-      continue;
-    }
-    if (ts.isPropertyAccessExpression(root) || ts.isElementAccessExpression(root)) {
-      root = root.expression;
-      continue;
-    }
-    if (ts.isCallExpression(root) || ts.isNewExpression(root)) {
-      root = root.expression;
-      continue;
-    }
-    if (ts.isExpressionWithTypeArguments(root)) {
-      root = root.expression;
-      continue;
-    }
-    if (ts.isTaggedTemplateExpression(root)) {
-      root = root.tag;
-      continue;
-    }
-    break;
-  }
-  if (!ts.isIdentifier(root)) return null;
   // PROBE resolution: every caller asks "is this chain ambient-rooted?"
   // and proceeds to its ordinary lowering on a null answer — so the
   // question must not carry resolution's side effects. Bare
@@ -378,12 +347,57 @@ export function ambientUndefVarRootOf(L: Lowerer, e: ts.Expression): ts.Identifi
   // diagnostics onto the build (reached-only-by-the-probe declarations
   // reported eagerly — collectGlobals runs this walk on every
   // initializer) and throws the cross-block merged-namespace fence's
-  // PoisonError out of collection entirely. The collect-phase guard
-  // suppresses both; the ordinary lowering that follows a null answer
-  // re-resolves with full effects at its own site.
+  // PoisonError out of collection entirely. The collect-phase guard also
+  // covers exact FFI ownership checks encountered while walking the chain;
+  // the ordinary lowering that follows a null answer re-resolves with full
+  // effects at its own site.
   const wasCollecting = L.collecting;
   L.collecting = true;
   try {
+    let root: ts.Expression = e;
+    for (;;) {
+      if (
+        ts.isParenthesizedExpression(root) ||
+        ts.isNonNullExpression(root) ||
+        ts.isAsExpression(root) ||
+        ts.isSatisfiesExpression(root) ||
+        ts.isTypeAssertion(root)
+      ) {
+        root = root.expression;
+        continue;
+      }
+      if (ts.isPropertyAccessExpression(root) || ts.isElementAccessExpression(root)) {
+        root = root.expression;
+        continue;
+      }
+      if (ts.isCallExpression(root) || ts.isNewExpression(root)) {
+        if (
+          ts.isCallExpression(root) &&
+          ts.isIdentifier(root.expression) &&
+          L.ffiImportsByName.has(root.expression.text)
+        ) {
+          const symbol = L.resolveValueSymbol(root.expression);
+          if (symbol && L.ownsValidatedFfiSymbol(root.expression.text, symbol)) {
+            // The manifest supplies this exact ambient declaration. Stop at
+            // the call boundary so normal lowering can emit the native call
+            // or its existing call-shape diagnostic.
+            return null;
+          }
+        }
+        root = root.expression;
+        continue;
+      }
+      if (ts.isExpressionWithTypeArguments(root)) {
+        root = root.expression;
+        continue;
+      }
+      if (ts.isTaggedTemplateExpression(root)) {
+        root = root.tag;
+        continue;
+      }
+      break;
+    }
+    if (!ts.isIdentifier(root)) return null;
     const sym = L.resolveValueSymbol(root);
     if (!sym) return null;
     if (L.trapBindings.has(sym)) return root;
diff --git a/packages/compiler/src/frontend/lowering/lowerer.ts b/packages/compiler/src/frontend/lowering/lowerer.ts
index dcd2999c2..95d5f9035 100644
--- a/packages/compiler/src/frontend/lowering/lowerer.ts
+++ b/packages/compiler/src/frontend/lowering/lowerer.ts
@@ -1264,6 +1264,15 @@ export class Lowerer {
       ? this.qualify(decl.getSourceFile(), `%cx${decl.getStart()}.${decl.name?.text ?? ""}`)
       : this.qualify(decl.getSourceFile(), nsPathPrefix(decl) + (decl.name ? decl.name.text : "%anon"));
 
+  /** Whether whole-program validation assigned this exact source symbol to
+   * the configured native binding. Name agreement alone never owns a call. */
+  ownsValidatedFfiSymbol(name: string, symbol: ts.Symbol): boolean {
+    return (
+      this.ffiImportsByName.has(name) &&
+      this.ffiBindingSymbols?.get(name)?.has(symbol) === true
+    );
+  }
+
   /** Follows import aliases to the original declaration's symbol. Every
    * value reference resolves through here, so it doubles as the flush
    * point for deferred collection diagnostics: resolving a reference to a
diff --git a/tests/harness/ffi.test.ts b/tests/harness/ffi.test.ts
index 644f103ea..2a31dd92e 100644
--- a/tests/harness/ffi.test.ts
+++ b/tests/harness/ffi.test.ts
@@ -21,7 +21,10 @@ const cacheRoot = join(
   flavor,
 );
 
+let cachedNativeArchive: string | undefined;
+
 function nativeArchive(): string {
+  if (cachedNativeArchive !== undefined) return cachedNativeArchive;
   const outDir = join(cacheRoot, "native");
   mkdirSync(outDir, { recursive: true });
   const object = join(outDir, "native.o");
@@ -35,21 +38,72 @@ function nativeArchive(): string {
     object,
   ]);
   execFileSync("ar", ["rcs", archive, object]);
-  return archive;
+  cachedNativeArchive = archive;
+  return cachedNativeArchive;
 }
 
-function manifest(archive: string): string {
+function manifest(archive: string, functionNames?: readonly string[]): string {
   const outDir = join(cacheRoot, "manifest");
   mkdirSync(outDir, { recursive: true });
   const profile = JSON.parse(
     readFileSync(join(fixtureRoot, "profile.json"), "utf8"),
-  ) as { libraries: string[] };
+  ) as { functions: { name: string }[]; libraries: string[] };
+  if (functionNames !== undefined) {
+    const names = new Set(functionNames);
+    profile.functions = profile.functions.filter((entry) => names.has(entry.name));
+  }
   profile.libraries = [archive];
   const path = join(outDir, "profile.json");
   writeFileSync(path, JSON.stringify(profile, null, 2));
   return path;
 }
 
+async function compileScaleFixture(
+  id: string,
+  body: readonly string[],
+  options: {
+    backend?: "c" | "llvm";
+    emitIr?: boolean;
+    ffi?: boolean;
+  } = {},
+) {
+  const outDir = join(cacheRoot, id);
+  mkdirSync(outDir, { recursive: true });
+  const entry = join(outDir, "main.ts");
+  writeFileSync(
+    entry,
+    [
+      "declare function nativeScale(value: number): number;",
+      ...body,
+      "",
+    ].join("\n"),
+  );
+  const result = await compile(entry, {
+    outDir,
+    outPath: join(outDir, "program"),
+    backend: options.backend ?? "c",
+    sanitize,
+    ...(options.ffi === false
+      ? {}
+      : { ffiProfilePath: manifest(nativeArchive(), ["nativeScale"]) }),
+    emitIr: options.emitIr,
+  });
+  return { entry, result };
+}
+
+function expectUndefinedAmbient(binaryPath: string): void {
+  const native = spawnSync(binaryPath, [], { encoding: "utf8" });
+  expect({
+    stdout: native.stdout,
+    stderr: native.stderr,
+    status: native.status,
+  }).toEqual({
+    stdout: "",
+    stderr: "Uncaught ReferenceError: nativeScale is not defined\n",
+    status: 1,
+  });
+}
+
 const expected = [
   "42",
   "true false",
@@ -82,6 +136,169 @@ describe.each(["c", "llvm"] as const)("outbound native FFI, %s backend", (backen
   });
 });
 
+describe.each(["c", "llvm"] as const)("FFI binding initializers, %s backend", (backend) => {
+  test("preserves exact calls across binding and early-probe contexts", async () => {
+    const { result } = await compileScaleFixture(
+      `binding-initializer-${backend}`,
+      [
+        "const moduleResult = nativeScale(2);",
+        "function main(): void {",
+        "  const functionResult = nativeScale(21);",
+        "  let once = nativeScale(3);",
+        "  console.log('module:', moduleResult);",
+        "  console.log('const:', functionResult);",
+        "  console.log('let:', once);",
+        "  for (const value of [1, 2]) {",
+        "    const loopResult = nativeScale(value);",
+        "    console.log('loop:', loopResult);",
+        "  }",
+        "  let assigned = 0;",
+        "  assigned = nativeScale(5);",
+        "  console.log('assignment:', assigned);",
+        "  const text = nativeScale(6).toString();",
+        "  console.log('chain:', text);",
+        "  let calls = 0;",
+        "  const sideEffectResult = nativeScale(++calls);",
+        "  console.log('side effect:', sideEffectResult, calls);",
+        "}",
+        "main();",
+      ],
+      { backend, emitIr: true },
+    );
+    if (!result.ok) {
+      throw new Error(
+        result.diagnostics.map((d) => `${d.code}: ${d.message}`).join("\n"),
+      );
+    }
+
+    const native = spawnSync(result.binaryPath, [], { encoding: "utf8" });
+    expect({
+      stdout: native.stdout,
+      stderr: native.stderr,
+      status: native.status,
+    }).toEqual({
+      stdout: [
+        "module: 4",
+        "const: 42",
+        "let: 6",
+        "loop: 2",
+        "loop: 4",
+        "assignment: 10",
+        "chain: 12",
+        "side effect: 2 1",
+        "",
+      ].join("\n"),
+      stderr: "",
+      status: 0,
+    });
+
+    const ir = JSON.stringify(JSON.parse(readFileSync(result.irPath!, "utf8")));
+    expect(ir.match(/"kind":"ffiCall"/g)).toHaveLength(7);
+    expect(ir).not.toContain('"fn":"global.undefRead"');
+  });
+});
+
+test("keeps a no-manifest ambient initializer failure ahead of its arguments", async () => {
+  const { result } = await compileScaleFixture(
+    "binding-initializer-no-manifest",
+    [
+      "function argument(): number {",
+      "  console.log('argument evaluated');",
+      "  return 21;",
+      "}",
+      "const result = nativeScale(argument());",
+      "console.log(result);",
+    ],
+    { emitIr: true, ffi: false },
+  );
+  if (!result.ok) {
+    throw new Error(
+      result.diagnostics.map((d) => `${d.code}: ${d.message}`).join("\n"),
+    );
+  }
+
+  expectUndefinedAmbient(result.binaryPath);
+
+  const ir = JSON.stringify(JSON.parse(readFileSync(result.irPath!, "utf8")));
+  expect(ir).toContain('"fn":"global.undefRead"');
+  expect(ir).not.toContain('"kind":"ffiCall"');
+});
+
+test.each([
+  {
+    id: "alias",
+    name: "an alias read",
+    body: [
+      "const alias = nativeScale;",
+      "console.log(alias(21));",
+    ],
+  },
+  {
+    id: "call-property",
+    name: "a .call use",
+    body: ["console.log(nativeScale.call(null, 21));"],
+  },
+  {
+    id: "parenthesized-callee",
+    name: "a parenthesized callee",
+    body: ["console.log((nativeScale)(21));"],
+  },
+])("does not widen $name into a native call", async ({ id, body }) => {
+  const { result } = await compileScaleFixture(`indirect-${id}`, body);
+  if (!result.ok) {
+    throw new Error(
+      result.diagnostics.map((d) => `${d.code}: ${d.message}`).join("\n"),
+    );
+  }
+
+  expectUndefinedAmbient(result.binaryPath);
+});
+
+test.each([
+  {
+    id: "optional",
+    name: "an optional direct call",
+    call: "nativeScale?.(21)",
+    message: "direct, non-generic calls only",
+  },
+  {
+    id: "spread",
+    name: "a spread direct call",
+    call: "nativeScale(...([21] as [number]))",
+    message: "spread arguments do not have a fixed native ABI",
+  },
+  {
+    id: "arity",
+    name: "a wrong-arity direct call",
+    call: "nativeScale()",
+    message: "native ABI requires exactly 1",
+    suppressTypeScript: true,
+  },
+])("keeps the existing FFI diagnostic for $name", async ({
+  id,
+  call,
+  message,
+  suppressTypeScript,
+}) => {
+  const { entry, result } = await compileScaleFixture(
+    `call-diagnostic-${id}`,
+    [
+      "function main(): void {",
+      ...(suppressTypeScript ? ["  // @ts-ignore exercise the native arity diagnostic"] : []),
+      `  const result = ${call};`,
+      "}",
+      "main();",
+    ],
+  );
+  expect(result.ok).toBe(false);
+  if (!result.ok) {
+    expect(result.diagnostics).toHaveLength(1);
+    expect(result.diagnostics[0]?.code).toBe("SC5003");
+    expect(result.diagnostics[0]?.message).toContain(message);
+    expect(result.diagnostics[0]?.loc.file).toBe(entry);
+  }
+});
+
 test("manifest validation is strict and source-facing", () => {
   const path = join(cacheRoot, "invalid.json");
   mkdirSync(cacheRoot, { recursive: true });
@@ -237,7 +454,8 @@ describe.each(["c", "llvm"] as const)("FFI binding identity, %s backend", (backe
           "declare function nativeScale(value: number): number;",
           "function localUse(): number {",
           "  function nativeScale(value: number): number { return value + 1; }",
-          "  return nativeScale(21);",
+          "  const result = nativeScale(21);",
+          "  return result;",
           "}",
           "console.log(localUse());",
           "",