core/cli: multiline \"\"\" input and /edit via EDITOR

Add triple-quote block messages in the REPL and /edit to compose a turn
in $EDITOR (temp file). Empty multiline or empty edit cancels.

CLAUDE.md

@@ -114,15 +114,15 @@ Basedpyright `recommended`. Ruff includes `ANN` (private return types `ANN202` i
   - G1: `ReasoningDeltaEvent`, `/stream`, `/verbose`
   - G2: `/rename`, `/delete` (confirm), `/export md|json`
   - G2.5: Click slash registry (`cli/slash.py`) + `awaitlet` for sync Click / async memory; auto `/help`; completer from `slash.list_commands`
+  - G3: multiline `"""` … `"""` input (`cli/input_text.py`); `/edit` via `$EDITOR` (`edit_text_in_editor`)
 
   **Planned**
 
-  - **G3 — Input**: multiline (`"""` … `"""`) and/or `/edit` via `$EDITOR`
   - **G4 — One-shot**: `plyngent chat -p/--prompt` (and stdin non-TTY); exit codes; non-interactive safety (`--yes` / deny destructive)
   - **G5 — Hardening**: tool timeouts/defaults review, config error clarity, cancel edges, optional `--log-level`, no secrets in status/export
   - **G6 — Docs**: real README, example TOML, CLAUDE/help accuracy
 
-  Milestone order: G3 → G4 → G5 → G6.
+  Milestone order: G4 → G5 → G6.
 
 - **Phase H**: multi-tenant platform (`router/`, auth, sandboxed tools, web).
 

src/plyngent/cli/editor.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import contextlib
 import os
 import shlex
 import subprocess
@@ -60,13 +61,23 @@ def ensure_config_file(path: Path) -> None:
         _ = path.write_text(_MINIMAL_CONFIG, encoding="utf-8")
 
 
-def open_in_editor(path: Path, *, editor: str | None = None) -> None:
-    """Open ``path`` with ``EDITOR`` (supports values like ``codium --wait``)."""
+def open_in_editor(
+    path: Path,
+    *,
+    editor: str | None = None,
+    ensure_exists: bool = True,
+) -> None:
+    """Open ``path`` with ``EDITOR`` (supports values like ``codium --wait``).
+
+    When ``ensure_exists`` is true (default), create a minimal config template
+    if the file is missing (used for ``plyngent config edit``).
+    """
     editor_cmd = editor if editor is not None else get_editor()
     if editor_cmd is None:
         msg = "EDITOR is not set"
         raise click.ClickException(msg)
 
+    if ensure_exists:
         ensure_config_file(path)
     try:
         argv = [*shlex.split(editor_cmd, posix=os.name != "nt"), str(path)]
@@ -91,6 +102,40 @@ def open_in_editor(path: Path, *, editor: str | None = None) -> None:
         raise click.ClickException(msg)
 
 
+def edit_text_in_editor(initial: str = "", *, suffix: str = ".md") -> str | None:
+    """Edit ``initial`` in ``$EDITOR``; return text or ``None`` if empty/cancelled.
+
+    Uses a temporary file. Does not create a config template.
+    """
+    import tempfile
+
+    if get_editor() is None:
+        msg = "EDITOR is not set; cannot /edit"
+        raise click.ClickException(msg)
+
+    with tempfile.NamedTemporaryFile(
+        mode="w",
+        encoding="utf-8",
+        suffix=suffix,
+        prefix="plyngent-edit-",
+        delete=False,
+    ) as handle:
+        path = Path(handle.name)
+        _ = handle.write(initial)
+
+    try:
+        open_in_editor(path, ensure_exists=False)
+        text = path.read_text(encoding="utf-8")
+    finally:
+        with contextlib.suppress(OSError):
+            path.unlink(missing_ok=True)
+
+    cleaned = text.rstrip("\n")
+    if not cleaned.strip():
+        return None
+    return cleaned
+
+
 def prompt_edit_config(path: Path, *, reason: str | None = None) -> bool:
     """If ``EDITOR`` is set, ask whether to edit ``path``. Returns True if opened."""
     if get_editor() is None:

src/plyngent/cli/input_text.py

@@ -0,0 +1,125 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+import click
+
+if TYPE_CHECKING:
+    from collections.abc import Callable
+
+_TRIPLE = '"""'
+
+
+def parse_triple_quote_line(line: str) -> tuple[str, bool] | None:
+    """If ``line`` starts a ``\"\"\"`` block, return ``(content_so_far, complete)``.
+
+    ``complete`` is True when the closing marker is on the same line
+    (e.g. ``\"\"\"hello\"\"\"`` → ``(\"hello\", True)``).
+    """
+    stripped = line.strip()
+    if not stripped.startswith(_TRIPLE):
+        return None
+    rest = stripped[len(_TRIPLE) :]
+    if rest.endswith(_TRIPLE) and len(rest) >= len(_TRIPLE):
+        inner = rest[: -len(_TRIPLE)]
+        return inner, True
+    return rest, False
+
+
+def finish_triple_quote_line(line: str) -> tuple[str, bool]:
+    """Parse a continuation line. Returns ``(content_piece, is_closer)``."""
+    stripped = line.strip()
+    if stripped == _TRIPLE:
+        return "", True
+    # Allow closing as trailing """ on a content line.
+    if line.rstrip().endswith(_TRIPLE):
+        without = line.rstrip()[: -len(_TRIPLE)]
+        # Don't treat a line that is only """ as content (handled above).
+        return without.rstrip("\n"), True
+    return line, False
+
+
+def assemble_multiline(
+    opening_line: str,
+    *,
+    read_line: Callable[[], str],
+    echo: Callable[[str], None] | None = None,
+) -> str | None:
+    """Read a full triple-quoted message. Empty body → ``None`` (cancel)."""
+    parsed = parse_triple_quote_line(opening_line)
+    if parsed is None:
+        text = opening_line.strip()
+        return text or None
+    first, complete = parsed
+    if complete:
+        return first if first.strip() else None
+
+    parts: list[str] = []
+    if first:
+        parts.append(first)
+    if echo is not None:
+        echo(f"(multiline; end with {_TRIPLE})")
+    while True:
+        try:
+            line = read_line()
+        except EOFError, KeyboardInterrupt:
+            if echo is not None:
+                echo("")
+                echo("cancelled")
+            return None
+        piece, done = finish_triple_quote_line(line)
+        if done:
+            if piece:
+                parts.append(piece)
+            break
+        parts.append(piece)
+    text = "\n".join(parts)
+    return text if text.strip() else None
+
+
+def _default_prompt() -> str:
+    return input("> ")
+
+
+def _default_cont() -> str:
+    return input("... ")
+
+
+def _default_echo(message: str) -> None:
+    click.echo(message)
+
+
+def read_repl_entry(
+    *,
+    read_line: Callable[[], str] | None = None,
+    echo: Callable[[str], None] | None = None,
+) -> str | None:
+    """Read one REPL entry (slash line, single line, or multiline).
+
+    Returns:
+        ``None`` — empty line or cancelled multiline (caller should re-prompt).
+        ``str`` starting with ``/`` — slash command line (stripped).
+        other ``str`` — user message text (may contain newlines).
+    """
+    _read = read_line if read_line is not None else _default_prompt
+    _echo = echo if echo is not None else _default_echo
+
+    try:
+        first = _read()
+    except EOFError:
+        raise
+    except KeyboardInterrupt:
+        _echo("")
+        return None
+
+    stripped = first.strip()
+    if not stripped:
+        return None
+    if stripped.startswith("/") and parse_triple_quote_line(stripped) is None:
+        return stripped
+
+    if parse_triple_quote_line(first) is not None:
+        cont_read = read_line if read_line is not None else _default_cont
+        return assemble_multiline(first, read_line=cont_read, echo=_echo)
+
+    return stripped

src/plyngent/cli/repl.py

@@ -4,6 +4,7 @@ from typing import TYPE_CHECKING
 
 import click
 
+from plyngent.cli.input_text import read_repl_entry
 from plyngent.cli.readline_setup import setup_readline
 from plyngent.cli.retry import run_user_text_with_retries
 from plyngent.cli.slash import handle_slash
@@ -12,9 +13,13 @@ if TYPE_CHECKING:
     from plyngent.cli.state import ReplState
 
 
-def _read_line() -> str:
-    """Blocking readline input (intentional for TTY REPL)."""
-    return input("> ").strip()
+def _echo_user(text: str) -> None:
+    click.secho("user: ", fg="green", nl=False)
+    if "\n" in text:
+        click.echo()
+        click.echo(text)
+    else:
+        click.echo(text)
 
 
 async def run_repl(state: ReplState) -> None:
@@ -27,26 +32,28 @@ async def run_repl(state: ReplState) -> None:
         f"stream={'on' if state.agent.stream else 'off'}  "
         f"verbose={'on' if state.verbose else 'off'}"
     )
-    click.echo("Type /help for commands. Empty line is ignored.")
+    click.echo('Type /help for commands. Multiline: """ … """. Empty line is ignored.')
 
     while True:
         try:
-            line = _read_line()
+            entry = read_repl_entry()
         except EOFError:
             click.echo()
             break
-        except KeyboardInterrupt:
-            click.echo()
+
+        if entry is None:
             continue
 
-        if not line:
-            continue
-        if line.startswith("/"):
-            cont = await handle_slash(state, line)
+        if entry.startswith("/"):
+            cont = await handle_slash(state, entry)
             if not cont:
                 break
+            if state.pending_user_text is not None:
+                text = state.pending_user_text
+                state.pending_user_text = None
+                _echo_user(text)
+                _ = await run_user_text_with_retries(state.agent, text)
             continue
 
-        click.secho("user: ", fg="green", nl=False)
-        click.echo(line)
-        _ = await run_user_text_with_retries(state.agent, line)
+        _echo_user(entry)
+        _ = await run_user_text_with_retries(state.agent, entry)

src/plyngent/cli/slash.py

@@ -30,15 +30,18 @@ _COMPACT_PREVIEW = 400
 _ON_OFF_CHOICES = ("on", "off")
 _EXPORT_FORMAT_CHOICES = ("md", "json")
 
-HELP_FOOTER = """\
-User messages are saved immediately. On API errors or Ctrl+C, partial
-assistant/tool output is discarded but the user message stays (so /retry
-works after resume, not only via readline history). Auto-retry: 10s/20s/30s.
-
-Tab completes slash commands and some arguments (provider, model, tools,
-stream, verbose, export). Use --session ID or /resume to continue a prior
-chat after restart.
-"""
+HELP_FOOTER = (
+    "User messages are saved immediately. On API errors or Ctrl+C, partial\n"
+    "assistant/tool output is discarded but the user message stays (so /retry\n"
+    "works after resume, not only via readline history). Auto-retry: 10s/20s/30s.\n"
+    "\n"
+    "Tab completes slash commands and some arguments (provider, model, tools,\n"
+    "stream, verbose, export). Use --session ID or /resume to continue a prior\n"
+    "chat after restart.\n"
+    "\n"
+    'Multiline: start a message with """ then end a later line with """.\n'
+    "Long prompts: /edit opens $EDITOR.\n"
+)
 
 
 class ReplExitError(Exception):
@@ -268,6 +271,28 @@ def clear_cmd(state: ReplState) -> None:
     click.echo("conversation cleared (in-memory only; DB history kept)")
 
 
+@slash.command("edit")
+@click.pass_obj
+def edit_cmd(state: ReplState) -> None:
+    """Compose a user message in ``$EDITOR``, then send it.
+
+    Opens a temporary buffer; save and quit the editor to submit.
+    Empty buffer cancels. Requires ``EDITOR`` (e.g. ``codium --wait``).
+    """
+    from plyngent.cli.editor import edit_text_in_editor
+
+    try:
+        text = edit_text_in_editor("")
+    except click.ClickException as exc:
+        click.echo(f"error: {exc}")
+        return
+    if text is None:
+        click.echo("edit cancelled (empty)")
+        return
+    state.pending_user_text = text
+    click.echo(f"(edit) {len(text)} characters ready to send")
+
+
 @slash.command("status")
 @click.pass_obj
 def status_cmd(state: ReplState) -> None:

src/plyngent/cli/state.py

@@ -31,6 +31,8 @@ class ReplState:
     max_rounds: int = DEFAULT_MAX_ROUNDS
     stream_enabled: bool = True
     verbose: bool = False
+    # Set by /edit; REPL sends as the next user turn then clears.
+    pending_user_text: str | None = None
     client: ChatClient = field(init=False)
     agent: ChatAgent = field(init=False)
     session_id: int | None = None

tests/test_cli/test_editor.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
+from pathlib import Path
 
 import pytest
 from click.testing import CliRunner
@@ -14,9 +14,6 @@ from plyngent.cli.editor import (
     resolve_config_path,
 )
 
-if TYPE_CHECKING:
-    from pathlib import Path
-
 
 def test_get_editor(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.delenv("EDITOR", raising=False)
@@ -66,6 +63,42 @@ def test_open_in_editor_missing_editor(tmp_path: Path, monkeypatch: pytest.Monke
         open_in_editor(tmp_path / "x.toml", editor=None)
 
 
+def test_edit_text_in_editor(monkeypatch: pytest.MonkeyPatch) -> None:
+    from plyngent.cli.editor import edit_text_in_editor
+
+    def fake_run(argv: list[str], check: bool = False) -> object:
+        del check
+        path = Path(argv[-1])
+        _ = path.write_text("hello from editor\n", encoding="utf-8")
+
+        class Result:
+            returncode: int = 0
+
+        return Result()
+
+    monkeypatch.setenv("EDITOR", "true")
+    monkeypatch.setattr("plyngent.cli.editor.subprocess.run", fake_run)
+    assert edit_text_in_editor("seed") == "hello from editor"
+
+
+def test_edit_text_empty_cancels(monkeypatch: pytest.MonkeyPatch) -> None:
+    from plyngent.cli.editor import edit_text_in_editor
+
+    def fake_run(argv: list[str], check: bool = False) -> object:
+        del check
+        path = Path(argv[-1])
+        _ = path.write_text("  \n", encoding="utf-8")
+
+        class Result:
+            returncode: int = 0
+
+        return Result()
+
+    monkeypatch.setenv("EDITOR", "true")
+    monkeypatch.setattr("plyngent.cli.editor.subprocess.run", fake_run)
+    assert edit_text_in_editor("") is None
+
+
 def test_prompt_edit_no_editor(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.delenv("EDITOR", raising=False)
     assert prompt_edit_config(tmp_path / "p.toml") is False

tests/test_cli/test_input_text.py

@@ -0,0 +1,61 @@
+from __future__ import annotations
+
+from plyngent.cli.input_text import (
+    assemble_multiline,
+    finish_triple_quote_line,
+    parse_triple_quote_line,
+    read_repl_entry,
+)
+
+
+def test_parse_same_line_block() -> None:
+    assert parse_triple_quote_line('"""hello"""') == ("hello", True)
+    assert parse_triple_quote_line('  """hi"""  ') == ("hi", True)
+
+
+def test_parse_open_block() -> None:
+    assert parse_triple_quote_line('"""first') == ("first", False)
+    assert parse_triple_quote_line('"""') == ("", False)
+
+
+def test_parse_not_block() -> None:
+    assert parse_triple_quote_line("hello") is None
+    assert parse_triple_quote_line("/help") is None
+
+
+def test_finish_closer() -> None:
+    assert finish_triple_quote_line('"""') == ("", True)
+    assert finish_triple_quote_line('last line"""') == ("last line", True)
+    assert finish_triple_quote_line("middle") == ("middle", False)
+
+
+def test_assemble_multiline() -> None:
+    lines = iter(["line two", '"""'])
+    text = assemble_multiline(
+        '"""line one',
+        read_line=lambda: next(lines),
+    )
+    assert text == "line one\nline two"
+
+
+def test_assemble_empty_cancels() -> None:
+    lines = iter(['"""'])
+    assert assemble_multiline('"""', read_line=lambda: next(lines)) is None
+
+
+def test_read_repl_entry_slash() -> None:
+    assert read_repl_entry(read_line=lambda: "/status") == "/status"
+
+
+def test_read_repl_entry_simple() -> None:
+    assert read_repl_entry(read_line=lambda: "  hi  ") == "hi"
+
+
+def test_read_repl_entry_empty() -> None:
+    assert read_repl_entry(read_line=lambda: "   ") is None
+
+
+def test_read_repl_entry_multiline() -> None:
+    seq = iter(['"""a', "b", '"""'])
+    text = read_repl_entry(read_line=lambda: next(seq), echo=lambda _s: None)
+    assert text == "a\nb"

tests/test_cli/test_repl_commands.py

@@ -134,6 +134,20 @@ async def test_quit(state: ReplState) -> None:
     assert await handle_slash(state, "/quit") is False
 
 
+async def test_edit_sets_pending(
+    state: ReplState,
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    monkeypatch.setattr(
+        "plyngent.cli.editor.edit_text_in_editor",
+        lambda *a, **k: "composed message",
+    )
+    assert await handle_slash(state, "/edit") is True
+    assert state.pending_user_text == "composed message"
+    assert "characters ready" in capsys.readouterr().out
+
+
 async def test_new_and_sessions(state: ReplState, capsys: pytest.CaptureFixture[str]) -> None:
     first = state.session_id
     assert await handle_slash(state, "/new other") is True