diff --git a/src/claude_code_api/pty.py b/src/claude_code_api/pty.py
index c8e5744..92c24b8 100644
--- a/src/claude_code_api/pty.py
+++ b/src/claude_code_api/pty.py
@@ -59,9 +59,26 @@ _SNAPSHOT_INTERVAL = 10.0
 # Gap between the bracketed-paste closing marker and the Enter keystroke
 # in `PtyClaudeProcess.write()`. Claude's Ink-based TUI reads stdin in
 # chunks; if `\r` is glued to `ESC [ 201 ~` it gets absorbed by the
-# paste-event handler and Submit never fires. 50ms is enough on a slow
-# Pi for the TUI to surface the paste event before the Enter arrives.
-_SUBMIT_KEY_DELAY = 0.05
+# paste-event handler and Submit never fires. 250ms is conservative for
+# a slow Pi under load — observed 50ms races on opus-high turns where
+# the paste handler is still scheduling when Enter arrives.
+_SUBMIT_KEY_DELAY = 0.25
+
+# After sending Enter we poll the PTY output for the paste-indicator
+# (claude's TUI renders ``[Pasted text #...`` while the paste is still
+# buffered in the input box). If it's still there after this window,
+# Enter never registered — we retry up to ``_SUBMIT_RETRIES`` times.
+_SUBMIT_VERIFY_WINDOW = 1.5
+_SUBMIT_VERIFY_POLL = 0.1
+_SUBMIT_RETRIES = 3
+_PASTE_INDICATOR = b"[Pasted text"
+
+# Size of the most-recent slice of PTY output considered "the current
+# screen render" when verifying a submit. The TUI emits a full clear +
+# redraw per state change; the latest redraw fits comfortably in this
+# window, while earlier intermediate frames (which may still show the
+# paste indicator) live further back in the same buffer.
+_TUI_TAIL_WINDOW = 8192
 
 
 @dataclass(frozen=True)
@@ -326,6 +343,35 @@ class PtyClaudeProcess:
                 if overflow > 0:
                     del self._output_buffer[:overflow]
 
+    async def _wait_for_submit(self, pre_enter_len: int) -> bool:
+        """Poll the PTY output to confirm Enter actually submitted the paste.
+
+        Claude's TUI renders ``[Pasted text #N +M lines]`` in the input
+        box while the paste is still buffered (unsubmitted). After Enter
+        registers, the input clears and the TUI redraws — the next
+        screen render no longer contains the indicator.
+
+        We compare bytes written *after* the Enter write (``pre_enter_len``
+        was snapshotted just before). Within those new bytes, only the
+        most recent ``_TUI_TAIL_WINDOW`` matter — that's the current
+        rendered screen; earlier bytes are intermediate redraws (one of
+        which would still show the indicator).
+
+        Returns True once the indicator is absent from the recent tail,
+        False on timeout.
+        """
+        deadline = asyncio.get_running_loop().time() + _SUBMIT_VERIFY_WINDOW
+        while asyncio.get_running_loop().time() < deadline:
+            buf = self.captured_output()
+            new_bytes = buf[pre_enter_len:]
+            tail = new_bytes[-_TUI_TAIL_WINDOW:]
+            # Only check once the TUI has produced at least one redraw
+            # after our Enter (otherwise tail is empty / pre-render).
+            if tail and _PASTE_INDICATOR not in tail:
+                return True
+            await asyncio.sleep(_SUBMIT_VERIFY_POLL)
+        return False
+
     async def _snapshot_loop(self, snapshot_dir: pathlib.Path) -> None:
         """Periodically dump the captured PTY buffer to a file.
 
@@ -530,7 +576,37 @@ class PtyClaudeProcess:
         )
         n1 = await asyncio.to_thread(pty.write, paste_chunk)
         await asyncio.sleep(_SUBMIT_KEY_DELAY)
-        n2 = await asyncio.to_thread(pty.write, b"\r")
+        n2 = 0
+        for attempt in range(1, _SUBMIT_RETRIES + 1):
+            # Snapshot just before each Enter write so the verifier only
+            # looks at bytes the TUI produces in response to *this*
+            # Enter, not earlier renders (which still show the paste
+            # indicator from when the paste was first buffered).
+            pre_enter_len = len(self.captured_output())
+            n2 += await asyncio.to_thread(pty.write, b"\r")
+            submitted = await self._wait_for_submit(pre_enter_len)
+            if submitted:
+                if attempt > 1:
+                    _log.info(
+                        "write: session_id=%s SUBMIT registered after %d Enter(s)",
+                        self._session_id,
+                        attempt,
+                    )
+                break
+            _log.warning(
+                "write: session_id=%s Enter #%d did not clear paste indicator "
+                "(buf=%d bytes) — retrying",
+                self._session_id,
+                attempt,
+                len(self.captured_output()),
+            )
+        else:
+            _log.error(
+                "write: session_id=%s SUBMIT never registered after %d "
+                "Enter attempts — paste likely stuck in input box",
+                self._session_id,
+                _SUBMIT_RETRIES,
+            )
         _log.info(
             "write: session_id=%s SUBMIT done (paste=%d Enter=%d)",
             self._session_id,