diff --git a/src/commands/batch/cli.test.ts b/src/commands/batch/cli.test.ts
index 8071e46e1..0eb957d1f 100644
--- a/src/commands/batch/cli.test.ts
+++ b/src/commands/batch/cli.test.ts
@@ -66,7 +66,7 @@ test('batch structured interaction target is projected to positionals, not devic
   const result = await runCliCapture([
     'batch',
     '--steps',
-    '[{"command":"press","input":{"target":{"kind":"point","x":10,"y":20},"count":2}}]',
+    '[{"command":"press","input":{"target":{"kind":"point","x":10,"y":20},"count":2,"platform":"ios","udid":"sim-1"}}]',
     '--json',
   ]);
 
@@ -76,6 +76,21 @@ test('batch structured interaction target is projected to positionals, not devic
   assert.deepEqual(step?.positionals, ['10', '20']);
   assert.equal(step?.flags?.target, undefined);
   assert.equal(step?.flags?.count, 2);
+  assert.equal(step?.flags?.platform, 'ios');
+  assert.equal(step?.flags?.udid, 'sim-1');
+});
+
+test('batch rejects invalid structured step input before daemon projection', async () => {
+  const result = await runCliCapture([
+    'batch',
+    '--steps',
+    '[{"command":"focus","input":{"x":10}}]',
+  ]);
+
+  assert.equal(result.code, 1);
+  assert.equal(result.calls.length, 0);
+  assert.match(result.stderr, /Batch step 1 focus input is invalid: Expected y to be set\./);
+  assert.doesNotMatch(result.stderr, /undefined/);
 });
 
 test('batch rejects structured replay steps before daemon dispatch', async () => {
diff --git a/src/commands/batch/projection.ts b/src/commands/batch/projection.ts
index f689ef15a..c4e7cd819 100644
--- a/src/commands/batch/projection.ts
+++ b/src/commands/batch/projection.ts
@@ -14,7 +14,11 @@ const batchCommandNames = STRUCTURED_BATCH_COMMAND_NAMES satisfies readonly Daem
 
 export type BatchCommandName = (typeof batchCommandNames)[number];
 
-type PrepareDaemonCommandRequest = (command: string, input: CommandInput) => DaemonCommandRequest;
+type PrepareDaemonCommandRequest = (
+  command: string,
+  input: CommandInput,
+  stepNumber: number,
+) => DaemonCommandRequest;
 
 export function createBatchDaemonWriter(
   prepareDaemonCommandRequest: PrepareDaemonCommandRequest,
@@ -49,24 +53,12 @@ function readBatchDaemonStep(
   const command = readBatchStepCommand(record, stepNumber);
   const input = readBatchStepInput(record, stepNumber);
   const runtime = readBatchStepRuntime(record, stepNumber);
-  const prepared = prepareBatchStep(command, input, prepareDaemonCommandRequest);
-  return {
-    ...prepared,
-    runtime: runtime ?? prepared.runtime,
-  };
-}
-
-function prepareBatchStep(
-  command: BatchCommandName,
-  input: CommandInput,
-  prepareDaemonCommandRequest: PrepareDaemonCommandRequest,
-): DaemonBatchStep {
-  const prepared = prepareDaemonCommandRequest(command, input);
+  const prepared = prepareDaemonCommandRequest(command, input, stepNumber);
   return {
     command: prepared.command,
     positionals: prepared.positionals,
     flags: buildFlags(prepared.options),
-    runtime: prepared.options.runtime,
+    runtime: runtime ?? prepared.options.runtime,
   };
 }
 
diff --git a/src/commands/command-metadata.ts b/src/commands/command-metadata.ts
index 6c13f5e37..4b7bc14d5 100644
--- a/src/commands/command-metadata.ts
+++ b/src/commands/command-metadata.ts
@@ -24,10 +24,11 @@ export function listCommandMetadata(): AnyCommandMetadata[] {
 
 export function listMcpCommandMetadata(): AnyCommandMetadata[] {
   return listMcpExposedCommandNames().map((name) => {
-    if (!isCommandName(name)) {
+    const metadata = findCommandMetadata(name);
+    if (!metadata) {
       throw new Error(`Missing command metadata for MCP-exposed command: ${name}`);
     }
-    return getCommandMetadata(name);
+    return metadata;
   });
 }
 
@@ -39,6 +40,6 @@ export function isCommandName(name: string): name is CommandName {
   return commandMetadataMap.has(name as CommandName);
 }
 
-function getCommandMetadata(name: CommandName): AnyCommandMetadata {
-  return commandMetadataMap.get(name)!;
+export function findCommandMetadata(name: string): AnyCommandMetadata | undefined {
+  return commandMetadataMap.get(name as CommandName);
 }
diff --git a/src/commands/command-projection.ts b/src/commands/command-projection.ts
index fc8ce9613..83f48ff89 100644
--- a/src/commands/command-projection.ts
+++ b/src/commands/command-projection.ts
@@ -13,6 +13,8 @@ import { reactNativeDaemonWriters } from './react-native/index.ts';
 import { recordingDaemonWriters } from './recording/index.ts';
 import { replayDaemonWriters } from './replay/index.ts';
 import { systemDaemonWriters } from './system/index.ts';
+import { findCommandMetadata } from './command-metadata.ts';
+import { AppError } from '../utils/errors.ts';
 
 const daemonWriters = {
   ...appDaemonWriters,
@@ -36,12 +38,27 @@ export type { BatchCommandName };
 function prepareBatchDaemonCommandRequest(
   command: string,
   input: CommandInput,
+  stepNumber: number,
 ): DaemonCommandRequest {
   const writer = (daemonWriters as Readonly<Record<string, DaemonWriter>>)[command];
   if (!writer) {
     throw new Error(`Missing daemon writer for batch command: ${command}`);
   }
-  return writer(input);
+  const metadata = findCommandMetadata(command);
+  if (!metadata) {
+    throw new Error(`Missing command metadata for batch command: ${command}`);
+  }
+  try {
+    return writer(metadata.readInput(input) as CommandInput);
+  } catch (err) {
+    const message = err instanceof Error ? err.message : String(err);
+    throw new AppError(
+      'INVALID_ARGS',
+      `Batch step ${stepNumber} ${command} input is invalid: ${message}`,
+      undefined,
+      err,
+    );
+  }
 }
 
 export function prepareDaemonCommandRequest(