diff --git a/src/officecli/CommandBuilder.Batch.cs b/src/officecli/CommandBuilder.Batch.cs
index a1bdc134d..3f0571390 100644
--- a/src/officecli/CommandBuilder.Batch.cs
+++ b/src/officecli/CommandBuilder.Batch.cs
@@ -172,6 +172,13 @@ private static Command BuildBatchCommand(Option<bool> jsonOption)
             var bestEffort = result.GetValue(batchBestEffortOpt);
 
             string jsonText;
+            if (inlineCommands != null && inputFile != null)
+                throw new ArgumentException(
+                    "batch: --commands and --input are mutually exclusive. Pick one source.");
+            // '--input -' explicitly opts INTO stdin — don't emit the
+            // "stdin will be ignored" warning in that case, since stdin
+            // is exactly what will be read.
+            var inputIsStdinAlias = inputFile != null && inputFile.Name == "-";
             // BUG-R7-09 (F-6): previously --commands/--input/stdin were
             // silently prioritized in that order — passing two of them at
             // once dropped the lower-priority source with no warning, so
@@ -179,6 +186,15 @@ private static Command BuildBatchCommand(Option<bool> jsonOption)
             // command that already had --commands set. Reject the
             // combination loudly. (Detect stdin via Console.IsInputRedirected
             // to avoid spurious failures from interactive terminals.)
+            //
+            // Only probe stdin when all of these are true: an explicit
+            // non-stdin source will make us ignore stdin, the warning has not
+            // been disabled, and stdin is redirected. This is a correctness
+            // boundary for MCP: its stdin is the JSON-RPC transport. Starting
+            // a background Peek there and abandoning it after the timeout
+            // leaves a live reader that consumes the next JSON-RPC request.
+            // OFFICECLI_BATCH_ALLOW_STDIN_REDIRECT is enabled by McpServer, so
+            // MCP calls with --commands/--input must never touch stdin here.
             // IsInputRedirected alone is true for every non-interactive
             // invocation (cron, CI, `< /dev/null`, systemd), so the warning
             // below fired on effectively all scripted batch runs with only
@@ -186,7 +202,11 @@ private static Command BuildBatchCommand(Option<bool> jsonOption)
             // /dev/null redirect) with zero length carries no second payload
             // — skip the warning. Pipes (CanSeek=false) still warn: someone
             // is actively piping data that will be ignored.
-            bool stdinHasInput = Console.IsInputRedirected;
+            var hasExplicitNonStdinSource = inlineCommands != null
+                || (inputFile != null && !inputIsStdinAlias);
+            var shouldWarnAboutIgnoredStdin = hasExplicitNonStdinSource
+                && Environment.GetEnvironmentVariable("OFFICECLI_BATCH_ALLOW_STDIN_REDIRECT") == null;
+            bool stdinHasInput = shouldWarnAboutIgnoredStdin && Console.IsInputRedirected;
             if (stdinHasInput)
             {
                 // Peek with a short timeout: /dev/null and closed stdin hit
@@ -207,15 +227,7 @@ private static Command BuildBatchCommand(Option<bool> jsonOption)
                 }
                 catch { /* keep IsInputRedirected verdict */ }
             }
-            if (inlineCommands != null && inputFile != null)
-                throw new ArgumentException(
-                    "batch: --commands and --input are mutually exclusive. Pick one source.");
-            // '--input -' explicitly opts INTO stdin — don't emit the
-            // "stdin will be ignored" warning in that case, since stdin
-            // is exactly what will be read.
-            var inputIsStdinAlias = inputFile != null && inputFile.Name == "-";
-            if ((inlineCommands != null || (inputFile != null && !inputIsStdinAlias)) && stdinHasInput
-                && Environment.GetEnvironmentVariable("OFFICECLI_BATCH_ALLOW_STDIN_REDIRECT") == null)
+            if (stdinHasInput)
             {
                 Console.Error.WriteLine(
                     "Warning: batch is reading from --commands/--input but stdin is also redirected; "