diff --git a/codex-rs/core/src/unified_exec/session.rs b/codex-rs/core/src/unified_exec/session.rs
index 02465538ec..9d2198c574 100644
--- a/codex-rs/core/src/unified_exec/session.rs
+++ b/codex-rs/core/src/unified_exec/session.rs
@@ -31,8 +31,25 @@ pub(crate) struct OutputBufferState {
 
 impl OutputBufferState {
     pub(super) fn push_chunk(&mut self, chunk: Vec<u8>) {
-        self.total_bytes = self.total_bytes.saturating_add(chunk.len());
-        self.chunks.push_back(chunk);
+        if chunk.is_empty() {
+            return;
+        }
+
+        // On Windows (especially with ConPTY) output can arrive in many tiny chunks.
+        // Coalesce them to avoid pathological behavior in drain/collect paths.
+        const MAX_COALESCED_CHUNK_BYTES: usize = 8_192;
+
+        let mut chunk = chunk;
+        let chunk_len = chunk.len();
+        self.total_bytes = self.total_bytes.saturating_add(chunk_len);
+
+        if let Some(tail) = self.chunks.back_mut()
+            && tail.len().saturating_add(chunk_len) <= MAX_COALESCED_CHUNK_BYTES
+        {
+            tail.append(&mut chunk);
+        } else {
+            self.chunks.push_back(chunk);
+        }
 
         let mut excess = self
             .total_bytes
diff --git a/codex-rs/core/tests/suite/unified_exec.rs b/codex-rs/core/tests/suite/unified_exec.rs
index 9365834500..26da3048af 100644
--- a/codex-rs/core/tests/suite/unified_exec.rs
+++ b/codex-rs/core/tests/suite/unified_exec.rs
@@ -2427,14 +2427,15 @@ async fn windows_unified_exec_write_stdin_strips_escapes() -> Result<()> {
     } = builder.build(&server).await?;
 
     let open_call_id = "windows-uexec-open-stdin";
+    let script = "$esc=[char]27; while ($true) { $line=[Console]::In.ReadLine(); if ($null -eq $line) { break }; Write-Output ($esc + '[31mUEXEC-WINDOWS-STDIN' + $esc + '[0m') }";
     let open_args = json!({
-        "cmd": "powershell -NoLogo -NoProfile",
+        "cmd": script,
         "yield_time_ms": 2_000,
     });
 
     let stdin_call_id = "windows-uexec-stdin-escapes";
     let stdin_args = json!({
-        "chars": "Write-Output \"UEXEC-WINDOWS-STDIN\"\n",
+        "chars": "trigger\r\n",
         "session_id": 1000,
         "yield_time_ms": 5_000,
     });