fix(gates): read a terminal dialog reply as one multi-line turn

AGENTS.md

@@ -158,7 +158,8 @@ step-by-step checklist.
   - `factory.py` - Provider instantiation
 
 - **gates/**: Human-in-the-loop support
-  - `human.py` - Rich terminal UI for human gate interactions
+  - `human.py` - Rich terminal UI for human gate interactions. `read_multiline_lines(console, sentinel)` is the shared blocking multi-line stdin reader behind both the human gate's `.` sentinel (`MULTILINE_SENTINEL`) and the dialog gate's `/send` (`DIALOG_SUBMIT_SENTINEL`); it returns `(text, hit_eof)` because an EOF that yielded no text is a deliberate dismissal while the sentinel with no text is an empty submission. `sentinel` is keyword-only and required, since the two gates use different ones
+  - `dialog.py` - Dialog-mode gate. On a tty the main turn reads through `read_multiline_lines`, so a pasted block is one turn rather than one turn per line; off a tty it falls back to single-line `Prompt.ask`, where the sentinel has no effect — the `_reads_multiline_turn()` predicate states that rule once, and `_display_dialog_start` gates its sentinel hint on it so the banner never advertises a keystroke the reader ignores. Both submission guards compare against stripped text: the reader drops trailing newlines but keeps a whitespace-only line, so an exact `== ""` check would dispatch whitespace as a turn and turn Ctrl-D into a submission
 
 - **interrupt/**: Interactive workflow interruption (Esc/Ctrl+G to pause)
   - `listener.py` - Keyboard listener daemon thread for Esc/Ctrl+G detection

CHANGELOG.md

@@ -27,6 +27,37 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   entirely. See
   [`examples/claude-agent-sdk-setting-sources.yaml`](examples/claude-agent-sdk-setting-sources.yaml).
 
+### Fixed
+
+- **A multi-line reply to a terminal dialog is now one turn** (#509) —
+  dialog mode was the only free-text human-input surface that could not accept
+  a multi-line answer (`QuestionDef.multiline` defaults to `True` and
+  `GateOption.multiline` opts in, both served by one reader in `gates/human.py`).
+  The dialog gate read a reply with single-line `Prompt.ask`, so pasting a block
+  of text into an interactive terminal dispatched *each line* as its own turn: a
+  three-line paste became three separate questions to the model, each answered
+  against a fragment, and the paste's trailing newline added a fourth turn with
+  empty content. Terminal turns now read through the multi-line reader already
+  behind the human gate's `.` sentinel, submitted with `/send` on its own line,
+  so internal newlines survive and a paste is a single message. An empty or
+  whitespace-only submission is no longer dispatched as a turn. A dismiss
+  keyword is recognised only once a turn is submitted, so on a tty `done` now
+  needs `/send` after it, and both the opening banner and the failure-recovery
+  notice say so rather than naming a keystroke that does nothing there.
+
+  Ctrl-D at the start of a line (Ctrl-Z then Enter on Windows) also submits the
+  lines entered so far, or dismisses the dialog when there are none. Because a
+  terminal's EOF does not persist, abandoning a part-written reply that way now
+  sends what was already entered and a second Ctrl-D is needed to leave, where
+  one used to exit; on an empty prompt it still exits in one keystroke.
+
+  The dialog uses `/send` where the human gate keeps `.`, since a lone `.` is
+  likelier to be prose in a conversational reply. Off a tty — a pipe or CI —
+  replies are still read one line at a time and `/send` has no effect; the one
+  change on that path is that a blank line is now skipped instead of dispatched
+  as an empty turn. The web dashboard is unaffected: it takes a separate path
+  that already delivered each message whole.
+
 ## [0.1.36](https://github.com/microsoft/conductor/compare/v0.1.35...v0.1.36) - 2026-09-02
 
 ### Added

docs/workflow-syntax.md

@@ -1198,6 +1198,7 @@ After the conversation, the agent re-executes with the dialog transcript as addi
 
 **Behavior notes:**
 - Dialog is supported on regular `agent` type only (not `human_gate`, `questions`, `script`, `workflow`, or `wait`)
+- In an interactive terminal, a reply may span multiple lines — paste or type freely and submit the turn with `/send` on its own line. A dismiss keyword ends the dialog the same way, so `done` needs `/send` after it there; off a tty every line is already a turn, so it does not. Ctrl-D at the start of a line (Ctrl-Z then Enter on Windows) also submits whatever lines have been entered so far, or dismisses the dialog when none have — so abandoning a part-written reply that way sends the lines already entered; press it on an empty prompt to leave without sending. An empty or whitespace-only submission is skipped rather than sent. Off a tty (a pipe or CI) replies are read one line at a time and `/send` does not apply, though a blank line is skipped rather than sent as an empty turn. The web dashboard is unaffected — its chat box takes a separate path that has always delivered each message whole, multi-line included
 - In web dashboard mode, the dialog temporarily replaces the graph area with a chat interface
 - When `--skip-gates` is set (e.g., CI/automation), dialogs are automatically skipped
 - The evaluator prompt should describe *when* to trigger dialog, not *what* to ask — the evaluator generates the opening question from the agent's output context

src/conductor/gates/dialog.py

@@ -11,6 +11,7 @@
 import asyncio
 import json
 import logging
+import sys
 import uuid
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Any
@@ -22,6 +23,11 @@
 
 from conductor.console import MarkupFreeConsole, make_console, styled
 from conductor.executor.linkify import linkify_markdown
+from conductor.gates.human import (
+    DIALOG_SUBMIT_SENTINEL,
+    read_multiline_lines,
+    read_on_daemon_thread,
+)
 
 if TYPE_CHECKING:
     from pathlib import Path
@@ -81,6 +87,38 @@
 _READY_MARKER = "[READY_TO_CONTINUE]"
 
 
+def _reads_multiline_turn() -> bool:
+    """Whether a conversational dialog turn is read multi-line.
+
+    Off a tty the turn falls back to a single-line ``Prompt.ask``, where the
+    submit sentinel has no effect. Both the reader in
+    ``DialogHandler._get_user_input`` and the opening banner's sentinel hint
+    ask this, so the banner can never advertise a keystroke the reader ignores.
+    """
+    return sys.stdin.isatty()
+
+
+def _dismiss_instruction() -> Text:
+    """How to actually leave the dialog, phrased for the active reader.
+
+    A dismiss keyword is only recognised once the turn is *submitted*, so on a
+    tty it needs the sentinel after it. Saying "type done" there describes a
+    keystroke that does nothing until the reply is sent -- the exit instruction
+    has to move with :func:`_reads_multiline_turn` or it contradicts the very
+    banner that advertises the sentinel.
+
+    Returns:
+        A pre-styled ``Text``, so a caller splices it through ``styled`` and
+        keeps its own template a literal (#406).
+    """
+    if _reads_multiline_turn():
+        return styled(
+            "send [bold]done[/bold] or [bold]/done[/bold] with [bold]{}[/bold]",
+            DIALOG_SUBMIT_SENTINEL,
+        )
+    return Text.from_markup("say [bold]done[/bold] or [bold]/done[/bold]")
+
+
 def _extract_ready_marker(response: str) -> tuple[bool, str]:
     """Return ``(proposed, cleaned)`` for an agent response.
 
@@ -273,6 +311,12 @@ async def handle_dialog(
                 result.user_dismissed = True
                 break
 
+            if not user_input.strip():
+                # Empty submission -- not a turn, and not dismissal either. On
+                # a tty this is a bare sentinel line; off a tty it is a blank
+                # line from the pipe, which ``Prompt.ask`` returns as "".
+                continue
+
             result.messages.append(DialogMessage(role="user", content=user_input))
             self._emit_event(
                 "dialog_message",
@@ -309,9 +353,9 @@ async def handle_dialog(
                     exc_info=True,
                 )
                 self.console.print(
-                    Text.from_markup(
-                        "[dim red]  (Agent response failed — you can continue "
-                        "or type 'done')[/dim red]"
+                    styled(
+                        "[dim red]  (Agent response failed — you can continue, or {})[/dim red]",
+                        _dismiss_instruction(),
                     )
                 )
                 continue
@@ -600,15 +644,40 @@ def _display_dialog_start(
         base_dir: Path | None = None,
     ) -> None:
         """Display the dialog opening with full agent context."""
+        # Advertised only where the sentinel applies -- see
+        # _reads_multiline_turn. Pre-rendered as a Text so the outer template
+        # has fixed arity: styled() splices a Text in with its own spans
+        # re-anchored, and raises IndexError on a template/argument mismatch
+        # that only the tty branch would reach. Off a tty the sentence keeps
+        # its original plural, since each line really is a separate response
+        # there.
+        instruction = (
+            styled(
+                "Type your response below. It can span multiple lines; send it"
+                " with [bold]{}[/bold] on its own line. A dismiss keyword ends"
+                " the dialog the same way: send [bold]done[/bold] or"
+                " [bold]/done[/bold] with [bold]{}[/bold].",
+                DIALOG_SUBMIT_SENTINEL,
+                DIALOG_SUBMIT_SENTINEL,
+            )
+            if _reads_multiline_turn()
+            # Byte-identical to upstream's sentence: off a tty every line is a
+            # turn already, so a dismiss keyword needs nothing after it.
+            else Text.from_markup(
+                "Type your responses below. Say [bold]done[/bold] or "
+                "[bold]/done[/bold] when finished."
+            )
+        )
+
         self.console.print()
         self.console.print(
             Panel(
                 styled(
                     "[bold]Agent '{}'[/bold] would like to discuss "
                     "its output with you.\n"
-                    "[dim]Type your responses below. Say [bold]done[/bold] or "
-                    "[bold]/done[/bold] when finished.[/dim]",
+                    "[dim]{}[/dim]",
                     agent.name,
+                    instruction,
                 ),
                 title=Text.from_markup("[bold magenta]Dialog Mode[/bold magenta]"),
                 border_style="magenta",
@@ -732,8 +801,26 @@ async def _get_user_input(
                 passing an interpolated f-string here.
 
         Returns:
-            User input text, or None on EOF/error.
+            User input text, or None on EOF/error, which the caller treats as
+            dismissal. The main turn (``prompt_text is None`` on a tty) reads
+            multi-line, so an EOF that *terminates a paste* returns the
+            accumulated content rather than dismissing; an EOF with nothing
+            but whitespace accumulated is a deliberate Ctrl-D and still
+            returns None.
         """
+        if prompt_text is None and _reads_multiline_turn():
+            self.console.print(styled("[bold magenta]You[/bold magenta]"))
+            try:
+                text, hit_eof = await read_on_daemon_thread(
+                    lambda: read_multiline_lines(self.console, sentinel=DIALOG_SUBMIT_SENTINEL)
+                )
+            except (EOFError, KeyboardInterrupt):
+                return None
+            if hit_eof and not text.strip():
+                # Ctrl-D at an empty prompt: the user is leaving, not pasting.
+                return None
+            return text
+
         prompt = styled("[bold magenta]You[/bold magenta]") if prompt_text is None else prompt_text
         try:
 

src/conductor/gates/human.py

@@ -32,12 +32,68 @@
 MULTILINE_SENTINEL = "."
 """Line that terminates a multi-line answer when typed on its own."""
 
+DIALOG_SUBMIT_SENTINEL = "/send"
+"""Line that submits a multi-line dialog turn.
+
+Distinct from :data:`MULTILINE_SENTINEL` because a lone ``.`` is likelier to
+be an ordinary line of prose in a conversational reply than in a gate answer.
+"""
+
 
 def _eof_key_hint() -> str:
     """Return the platform-appropriate EOF keystroke for display."""
     return "Ctrl-Z then Enter" if sys.platform == "win32" else "Ctrl-D"
 
 
+def read_multiline_lines(console: MarkupFreeConsole, *, sentinel: str) -> tuple[str, bool]:
+    """Read a multi-line answer from stdin (blocking; call on a thread).
+
+    Terminates on a line whose stripped text equals ``sentinel`` or on EOF.
+    Internal newlines are preserved; trailing empty lines are dropped, but a
+    trailing line of whitespace is kept verbatim -- a real strip would eat the
+    meaningful indentation of a pasted code block.
+
+    Args:
+        console: Console to print the input hint to.
+        sentinel: Line that, typed alone, submits the accumulated text.
+            Keyword-only and required: the two gates use different sentinels,
+            so a caller states which one it means.
+
+    Returns:
+        ``(text, hit_eof)`` -- the collected text and whether the read ended at
+        EOF rather than at the sentinel. Callers need the distinction because
+        an EOF that yielded no text is a deliberate dismissal (Ctrl-D at an
+        empty prompt), whereas the sentinel with no text is merely an empty
+        submission.
+    """
+    console.print(
+        styled(
+            "  [dim]Enter your answer. Finish with '{}' on its own line (or {}).[/dim]",
+            sentinel,
+            _eof_key_hint(),
+        )
+    )
+    lines: list[str] = []
+    hit_eof = False
+    while True:
+        try:
+            line = input()
+        except EOFError:
+            # The only end-of-input a real stdin produces here: an exhausted
+            # or non-tty stream raises EOFError, a closed one ValueError.
+            # StopIteration is deliberately *not* caught -- input() would only
+            # relay it from a contrived stdin replacement, and treating it as
+            # EOF would submit a truncated turn as if the user had pressed
+            # Ctrl-D. A test double that runs past what it supplied is a bug
+            # in the test, so it must surface rather than read as a dismissal.
+            hit_eof = True
+            break
+        if line.strip() == sentinel:
+            break
+        lines.append(line)
+    return "\n".join(lines).rstrip("\n"), hit_eof
+
+
 async def read_on_daemon_thread[T](fn: Callable[[], T]) -> T:
     """Run a blocking stdin read on a daemon thread and await its result.
 
@@ -477,30 +533,15 @@ def _ask_value() -> str:
     def _read_multiline(self) -> str:
         """Read a multi-line answer from stdin (blocking; call in a thread).
 
-        Terminates on a line containing only ``.`` or on EOF. The sentinel is
-        listed first in the hint because Ctrl-D/Ctrl-Z differs by platform.
+        Delegates to the shared :func:`read_multiline_lines` with this gate's
+        historical ``.`` sentinel.
 
         Returns:
-            The collected text with trailing blank lines stripped. Internal
-            newlines are preserved.
+            The collected text, with trailing empty lines dropped and internal
+            newlines preserved.
         """
-        self.console.print(
-            styled(
-                "  [dim]Enter your answer. Finish with '{}' on its own line (or {}).[/dim]",
-                MULTILINE_SENTINEL,
-                _eof_key_hint(),
-            )
-        )
-        lines: list[str] = []
-        while True:
-            try:
-                line = input()
-            except EOFError:
-                break
-            if line.strip() == MULTILINE_SENTINEL:
-                break
-            lines.append(line)
-        return "\n".join(lines).rstrip("\n")
+        text, _ = read_multiline_lines(self.console, sentinel=MULTILINE_SENTINEL)
+        return text
 
 
 @dataclass