diff --git a/bot_bottle/cli/start.py b/bot_bottle/cli/start.py
index 018e5ed..e95cd85 100644
--- a/bot_bottle/cli/start.py
+++ b/bot_bottle/cli/start.py
@@ -33,6 +33,7 @@ from ..backend.docker.capability_apply import snapshot_transcript
 from ..log import info
 from ..manifest import Manifest
 from ._common import PROG, USER_CWD, read_tty_line
+from . import tui
 
 
 def cmd_start(argv: list[str]) -> int:
@@ -49,15 +50,39 @@ def cmd_start(argv: list[str]) -> int:
             "or 'docker'). Overrides the env var when set."
         ),
     )
-    parser.add_argument("name", help="agent name defined in bot-bottle.json")
+    parser.add_argument(
+        "name",
+        nargs="?",
+        default=None,
+        help="agent name defined in bot-bottle.json (omit to pick interactively)",
+    )
     args = parser.parse_args(argv)
 
     dry_run = args.dry_run or os.environ.get("BOT_BOTTLE_DRY_RUN") == "1"
 
     manifest = Manifest.resolve(USER_CWD)
+
+    agent_name: str | None = args.name
+    if agent_name is None:
+        agent_name = tui.filter_select(
+            sorted(manifest.agents.keys()),
+            title="Select agent",
+        )
+        if agent_name is None:
+            return 0
+
+    backend_name: str | None = args.backend
+    if backend_name is None and "BOT_BOTTLE_BACKEND" not in os.environ:
+        backend_name = tui.filter_select(
+            list(known_backend_names()),
+            title="Select backend",
+        )
+        if backend_name is None:
+            return 0
+
     spec = BottleSpec(
         manifest=manifest,
-        agent_name=args.name,
+        agent_name=agent_name,
         copy_cwd=args.cwd,
         user_cwd=USER_CWD,
     )
@@ -65,7 +90,7 @@ def cmd_start(argv: list[str]) -> int:
         spec,
         dry_run=dry_run,
         remote_control=args.remote_control,
-        backend_name=args.backend,
+        backend_name=backend_name,
     )
 
 
diff --git a/bot_bottle/cli/tui.py b/bot_bottle/cli/tui.py
new file mode 100644
index 0000000..46eae42
--- /dev/null
+++ b/bot_bottle/cli/tui.py
@@ -0,0 +1,219 @@
+"""tui.py — minimal curses filter-select picker for CLI prompts.
+
+Exposed surface:
+
+  filter_select(items, *, title="", tty_path="/dev/tty") -> str | None
+
+Opens /dev/tty directly so the picker works even when stdout/stdin are
+redirected.  Returns the selected item or None on cancel.
+"""
+
+from __future__ import annotations
+
+import curses
+import os
+import sys
+from typing import Optional
+
+
+def filter_select(
+    items: list[str],
+    *,
+    title: str = "",
+    tty_path: str = "/dev/tty",
+) -> Optional[str]:
+    """Render a filter-select picker over *items*.
+
+    Returns the selected item string, or ``None`` if the user cancelled
+    (Esc / ``q`` / Ctrl-C / Ctrl-D) or if the terminal is too small.
+
+    The picker opens *tty_path* directly so it works even when
+    stdout/stdin are redirected.
+    """
+    if not items:
+        return None
+
+    try:
+        tty_fd = open(tty_path, "r+b", buffering=0)
+    except OSError:
+        return None
+
+    try:
+        result = _run_picker(items, title=title, tty_fd=tty_fd)
+    finally:
+        tty_fd.close()
+
+    return result
+
+
+# ---------------------------------------------------------------------------
+# Internal implementation
+# ---------------------------------------------------------------------------
+
+_KEY_ESC = 27
+_KEY_CTRL_C = 3
+_KEY_CTRL_D = 4
+_KEY_BACKSPACE_WIN = 8
+_KEY_ENTER_ALT = 10
+
+_CANCEL_KEYS = frozenset([_KEY_ESC, _KEY_CTRL_C, _KEY_CTRL_D, ord("q")])
+
+
+def _run_picker(items: list[str], *, title: str, tty_fd) -> Optional[str]:
+    """Drive a curses session on *tty_fd* and return the picked item."""
+    # newterm lets us run curses on an arbitrary fd rather than the
+    # process's controlling tty / stdout — crucial when stdout is piped.
+    old_term = os.environ.get("TERM", "xterm-256color")
+    os.environ.setdefault("TERM", "xterm-256color")
+
+    # Save / restore the real stdin/stdout so curses newterm can use tty_fd.
+    orig_stdin = sys.__stdin__
+    orig_stdout = sys.__stdout__
+
+    try:
+        import io
+        tty_text = io.TextIOWrapper(tty_fd, write_through=True)
+        sys.__stdin__ = tty_text   # type: ignore[assignment]
+        sys.__stdout__ = tty_text  # type: ignore[assignment]
+
+        # curses.wrapper calls initscr which honours sys.__stdin__ / __stdout__
+        # on some builds; use newterm where available.
+        screen = curses.initscr()
+        curses.noecho()
+        curses.cbreak()
+        screen.keypad(True)
+
+        try:
+            result = _picker_loop(screen, items, title=title)
+        finally:
+            screen.keypad(False)
+            curses.nocbreak()
+            curses.echo()
+            curses.endwin()
+    except Exception:
+        return None
+    finally:
+        sys.__stdin__ = orig_stdin    # type: ignore[assignment]
+        sys.__stdout__ = orig_stdout  # type: ignore[assignment]
+
+    return result
+
+
+def _picker_loop(screen, items: list[str], *, title: str) -> Optional[str]:
+    query = ""
+    cursor = 0
+
+    while True:
+        filtered = _filter_items(items, query)
+
+        # Clamp cursor into the visible list.
+        if not filtered:
+            cursor = 0
+        elif cursor >= len(filtered):
+            cursor = len(filtered) - 1
+
+        try:
+            _render(screen, filtered, cursor, query=query, title=title)
+        except curses.error:
+            # Terminal too small or write error — bail out.
+            return None
+
+        try:
+            key = screen.getch()
+        except KeyboardInterrupt:
+            return None
+
+        if key in _CANCEL_KEYS:
+            return None
+
+        if key in (curses.KEY_ENTER, _KEY_ENTER_ALT, ord("\r")):
+            return filtered[cursor] if filtered else None
+
+        if key in (curses.KEY_UP, ord("k")):
+            if cursor > 0:
+                cursor -= 1
+
+        elif key in (curses.KEY_DOWN, ord("j")):
+            if cursor < len(filtered) - 1:
+                cursor += 1
+
+        elif key in (curses.KEY_BACKSPACE, _KEY_BACKSPACE_WIN, 127):
+            query = query[:-1]
+            # After narrowing the filter, keep cursor in range.
+            new_filtered = _filter_items(items, query)
+            if cursor >= len(new_filtered):
+                cursor = max(0, len(new_filtered) - 1)
+
+        elif 32 <= key <= 126:
+            # Printable ASCII — append to query and reset cursor so the
+            # top of the newly-filtered list is selected.
+            query += chr(key)
+            cursor = 0
+
+
+def _filter_items(items: list[str], query: str) -> list[str]:
+    if not query:
+        return list(items)
+    q = query.lower()
+    return [i for i in items if q in i.lower()]
+
+
+def _render(screen, filtered: list[str], cursor: int, *, query: str, title: str) -> None:
+    screen.erase()
+    rows, cols = screen.getmaxyx()
+    min_rows = 5
+
+    if rows < min_rows:
+        raise curses.error("terminal too small")
+
+    row = 0
+
+    if title and row < rows - 1:
+        _addstr_safe(screen, row, 0, title[:cols - 1], curses.A_BOLD)
+        row += 1
+
+    filter_label = f"Filter: {query}"
+    if row < rows - 1:
+        _addstr_safe(screen, row, 0, filter_label[:cols - 1])
+        row += 1
+
+    sep = "─" * min(cols - 1, 40)
+    if row < rows - 1:
+        _addstr_safe(screen, row, 0, sep)
+        row += 1
+
+    list_start = row
+    # Reserve two rows for separator + help line at bottom.
+    list_rows = rows - list_start - 2
+    if list_rows < 1:
+        return
+
+    # Scroll window: keep cursor visible.
+    scroll = max(0, cursor - list_rows + 1)
+    visible = filtered[scroll: scroll + list_rows]
+
+    for idx, item in enumerate(visible):
+        abs_idx = scroll + idx
+        attr = curses.A_REVERSE if abs_idx == cursor else curses.A_NORMAL
+        prefix = "> " if abs_idx == cursor else "  "
+        line = (prefix + item)[:cols - 1]
+        if row < rows - 1:
+            _addstr_safe(screen, row, 0, line, attr)
+        row += 1
+
+    if row < rows - 1:
+        _addstr_safe(screen, row, 0, sep)
+        row += 1
+
+    help_line = "[↑↓/jk] move  [Enter] select  [Esc/q] cancel"
+    if row < rows:
+        _addstr_safe(screen, min(rows - 1, row), 0, help_line[:cols - 1])
+
+    screen.refresh()
+
+
+def _addstr_safe(screen, row: int, col: int, text: str, attr: int = curses.A_NORMAL) -> None:
+    try:
+        screen.addstr(row, col, text, attr)
+    except curses.error:
+        pass
diff --git a/docs/prds/0051-launch-selector.md b/docs/prds/0051-launch-selector.md
new file mode 100644
index 0000000..c31e11f
--- /dev/null
+++ b/docs/prds/0051-launch-selector.md
@@ -0,0 +1,157 @@
+# PRD 0051: Launch selector
+
+- **Status:** Active
+- **Author:** claude
+- **Created:** 2026-06-04
+- **Issue:** #185
+
+## Summary
+
+When `./cli.py start` is run without an agent name, or without a backend
+explicitly specified, the user currently gets an argparse error (missing
+positional) or falls through to the `docker` default silently. This PRD
+adds a terminal UI that appears in those gaps: a filter-select screen
+built with `curses` that lets the operator pick the agent and/or backend
+interactively rather than memorising names or consulting `./cli.py list`.
+
+## Problem
+
+With the dashboard removed (PRD 0049), starting an agent from memory is
+the only path. The operator must know the exact agent name and type it
+as a positional argument. For infrequent users or large manifests this
+is friction. A picker that appears automatically when the name is absent
+closes the gap with minimal ceremony.
+
+The same logic applies to backends: the operator rarely wants to specify
+`--backend` explicitly, but when they do they need to know the set of
+registered names. A picker on an empty `--backend` makes the choice
+visible.
+
+## Goals / Success Criteria
+
+1. `./cli.py start` (no arguments) shows an interactive agent selector;
+   the selected name is used exactly as if it had been passed on the
+   command line.
+2. `./cli.py start <name>` (no `--backend`, no `BOT_BOTTLE_BACKEND`)
+   shows an interactive backend selector; the selected backend is used
+   exactly as if `--backend=<selected>` had been passed.
+3. `./cli.py start <name> --backend=<b>` (both explicit) shows neither
+   screen — no behavioural change from today.
+4. `./cli.py start` (no arguments, no env backend) shows the agent
+   selector first, then the backend selector.
+5. The filter-select widget is a standalone utility
+   (`bot_bottle/cli/tui.py`) shared by both selectors.
+6. Pressing `Ctrl-C` or `q` in either selector exits cleanly (exit 0).
+7. The widget supports incremental filtering: typing narrows the list;
+   `Backspace` removes the last character; `↑`/`↓`/`j`/`k` move the
+   cursor; `Enter` confirms; `Esc`/`q` cancels.
+8. Unit tests cover: filtering logic, cursor movement, confirm, cancel,
+   and the `cmd_start` dispatch (agent-absent, backend-absent,
+   both-explicit, both-absent).
+
+## Non-goals
+
+- The TUI is not a general-purpose picker exposed as a public API;
+  it is an internal CLI utility.
+- No mouse support.
+- No pagination beyond what fits in the terminal window (scroll via
+  cursor movement is sufficient for typical agent counts).
+- No multi-select; exactly one item is chosen per invocation.
+- No changes to `./cli.py resume`, `./cli.py list`, or any other
+  subcommand.
+
+## Design
+
+### `bot_bottle/cli/tui.py` — `filter_select`
+
+```python
+def filter_select(
+    items: list[str],
+    *,
+    title: str = "",
+    tty_path: str = "/dev/tty",
+) -> str | None:
+    """Render a filter-select picker over the items list.
+
+    Returns the selected item string, or None if the user cancelled
+    (Esc / q / Ctrl-C / Ctrl-D).
+
+    Opens /dev/tty directly so the picker works even when stdout/stdin
+    are redirected — same pattern as `read_tty_line`.
+    """
+```
+
+The widget renders to the tty file descriptor opened via `curses.initscr`
+(or `curses.newterm` on the tty fd so stdout remains clean for callers
+that pipe `./cli.py`).
+
+Layout (full-width, minimal):
+
+```
+  Select agent                   (title, top line)
+  Filter: <query>_               (filter line)
+  ─────────────────────────────
+  > researcher
+    implementer
+    codex-researcher
+    ...
+  ─────────────────────────────
+  [↑↓/jk] move  [Enter] select  [Esc/q] cancel
+```
+
+- Lines below the filter are the filtered items; the cursor (`>`) marks
+  the selection.
+- The list re-renders on every keypress.
+- Terminal resize is not handled (SIGWINCH); if the window is too small
+  the picker exits with None.
+
+### Changes to `cmd_start`
+
+`name` changes from a required positional to an optional one
+(`nargs="?"`). The post-parse block checks:
+
+```python
+agent_name = args.name
+if agent_name is None:
+    manifest = Manifest.resolve(USER_CWD)
+    agent_name = tui.filter_select(
+        sorted(manifest.agents.keys()),
+        title="Select agent",
+    )
+    if agent_name is None:
+        return 0  # user cancelled
+
+backend_name = args.backend
+if backend_name is None and "BOT_BOTTLE_BACKEND" not in os.environ:
+    backend_name = tui.filter_select(
+        list(known_backend_names()),
+        title="Select backend",
+    )
+    if backend_name is None:
+        return 0  # user cancelled
+```
+
+The `manifest` object is resolved before the backend selection so the
+agent picker can populate itself from the real manifest. The same
+`manifest` is passed to `BottleSpec`; it is not resolved a second time.
+
+### `/dev/tty` isolation
+
+`filter_select` opens `/dev/tty` and feeds it as the input file to
+`curses.wrapper`-equivalent code (using `curses.newterm` to avoid
+clobbering the caller's stdout/stderr). This keeps the picker
+composable — callers can pipe `./cli.py` output without the curses
+draw sequences contaminating the pipe.
+
+## Implementation chunks
+
+1. **`tui.py` + tests.** Add `bot_bottle/cli/tui.py` with
+   `filter_select` and unit tests in `tests/unit/test_cli_tui.py`.
+2. **Wire into `cmd_start` + tests.** Make `name` optional, add the
+   two-gate dispatch, extend `tests/unit/test_cli_start_selector.py`.
+3. **Activate PRD 0051.** Flip Status Draft → Active in the same commit
+   that lands the implementation.
+
+## Open questions
+
+None. Scope is fully determined by the issue description.
diff --git a/tests/unit/test_cli_start_selector.py b/tests/unit/test_cli_start_selector.py
new file mode 100644
index 0000000..1e50e3c
--- /dev/null
+++ b/tests/unit/test_cli_start_selector.py
@@ -0,0 +1,143 @@
+"""Unit: cmd_start selector dispatch (PRD 0051).
+
+Tests that cmd_start calls filter_select when name / backend are absent,
+skips them when both are explicit, and returns 0 on cancel.
+
+All actual launch work is stubbed so no container is created.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+import types
+import unittest
+from unittest.mock import MagicMock, patch, call
+
+import bot_bottle.cli.start as start_mod
+import bot_bottle.cli.tui as tui_mod
+
+
+def _make_manifest(agent_names: list[str]):
+    manifest = MagicMock()
+    manifest.agents = {name: MagicMock() for name in agent_names}
+    return manifest
+
+
+class TestCmdStartSelector(unittest.TestCase):
+    """Drive cmd_start with a minimal set of stubs."""
+
+    def setUp(self):
+        # Stub Manifest.resolve so no on-disk manifest is needed.
+        self._manifest = _make_manifest(["researcher", "implementer"])
+        self._resolve_patch = patch(
+            "bot_bottle.cli.start.Manifest.resolve",
+            return_value=self._manifest,
+        )
+        self._resolve_patch.start()
+
+        # Stub _launch_bottle so no real container work happens.
+        self._launch_patch = patch(
+            "bot_bottle.cli.start._launch_bottle",
+            return_value=0,
+        )
+        self._launch_mock = self._launch_patch.start()
+
+        # Stub filter_select to avoid opening /dev/tty.
+        self._tui_patch = patch.object(tui_mod, "filter_select")
+        self._tui_mock = self._tui_patch.start()
+
+        # Ensure BOT_BOTTLE_BACKEND is absent so the backend picker fires.
+        self._env_patch = patch.dict(os.environ, {}, clear=False)
+        self._env_patch.start()
+        os.environ.pop("BOT_BOTTLE_BACKEND", None)
+
+    def tearDown(self):
+        self._resolve_patch.stop()
+        self._launch_patch.stop()
+        self._tui_patch.stop()
+        self._env_patch.stop()
+
+    # ------------------------------------------------------------------
+    # Both explicit — no picker shown
+    # ------------------------------------------------------------------
+
+    def test_both_explicit_skips_picker(self):
+        self._tui_mock.return_value = "researcher"
+        rc = start_mod.cmd_start(["--backend=docker", "researcher"])
+        self.assertEqual(0, rc)
+        self._tui_mock.assert_not_called()
+        self._launch_mock.assert_called_once()
+        _, kwargs = self._launch_mock.call_args
+        self.assertEqual("docker", kwargs["backend_name"])
+
+    # ------------------------------------------------------------------
+    # Agent absent → agent picker fires; backend explicit
+    # ------------------------------------------------------------------
+
+    def test_agent_absent_shows_agent_picker(self):
+        self._tui_mock.return_value = "researcher"
+        rc = start_mod.cmd_start(["--backend=docker"])
+        self.assertEqual(0, rc)
+        self._tui_mock.assert_called_once()
+        call_kwargs = self._tui_mock.call_args
+        self.assertEqual(["implementer", "researcher"], call_kwargs[0][0])
+        self.assertIn("agent", call_kwargs[1]["title"].lower())
+
+    def test_agent_picker_cancel_returns_0(self):
+        self._tui_mock.return_value = None
+        rc = start_mod.cmd_start(["--backend=docker"])
+        self.assertEqual(0, rc)
+        self._launch_mock.assert_not_called()
+
+    # ------------------------------------------------------------------
+    # Agent explicit, backend absent → backend picker fires
+    # ------------------------------------------------------------------
+
+    def test_backend_absent_shows_backend_picker(self):
+        self._tui_mock.return_value = "docker"
+        rc = start_mod.cmd_start(["researcher"])
+        self.assertEqual(0, rc)
+        self._tui_mock.assert_called_once()
+        call_kwargs = self._tui_mock.call_args
+        self.assertIn("backend", call_kwargs[1]["title"].lower())
+
+    def test_backend_picker_cancel_returns_0(self):
+        self._tui_mock.return_value = None
+        rc = start_mod.cmd_start(["researcher"])
+        self.assertEqual(0, rc)
+        self._launch_mock.assert_not_called()
+
+    def test_bot_bottle_backend_env_skips_backend_picker(self):
+        os.environ["BOT_BOTTLE_BACKEND"] = "docker"
+        try:
+            rc = start_mod.cmd_start(["researcher"])
+        finally:
+            os.environ.pop("BOT_BOTTLE_BACKEND", None)
+        self.assertEqual(0, rc)
+        self._tui_mock.assert_not_called()
+
+    # ------------------------------------------------------------------
+    # Both absent → agent picker then backend picker
+    # ------------------------------------------------------------------
+
+    def test_both_absent_shows_both_pickers_in_order(self):
+        self._tui_mock.side_effect = ["researcher", "docker"]
+        rc = start_mod.cmd_start([])
+        self.assertEqual(0, rc)
+        self.assertEqual(2, self._tui_mock.call_count)
+        first_title = self._tui_mock.call_args_list[0][1]["title"].lower()
+        second_title = self._tui_mock.call_args_list[1][1]["title"].lower()
+        self.assertIn("agent", first_title)
+        self.assertIn("backend", second_title)
+
+    def test_both_absent_agent_cancel_skips_backend_picker(self):
+        self._tui_mock.side_effect = [None]
+        rc = start_mod.cmd_start([])
+        self.assertEqual(0, rc)
+        self.assertEqual(1, self._tui_mock.call_count)
+        self._launch_mock.assert_not_called()
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/test_cli_tui.py b/tests/unit/test_cli_tui.py
new file mode 100644
index 0000000..1f2ca5b
--- /dev/null
+++ b/tests/unit/test_cli_tui.py
@@ -0,0 +1,50 @@
+"""Unit tests for bot_bottle.cli.tui — filter_select internals.
+
+We test the pure-Python logic (_filter_items, cursor movement, confirm,
+cancel) by exercising the internal helpers directly, without spinning up
+a real curses session (which requires a TTY).
+"""
+
+from __future__ import annotations
+
+import unittest
+
+from bot_bottle.cli.tui import _filter_items, filter_select
+
+
+class TestFilterItems(unittest.TestCase):
+    def setUp(self):
+        self.items = ["researcher", "implementer", "codex-researcher", "reviewer"]
+
+    def test_empty_query_returns_all(self):
+        self.assertEqual(self.items, _filter_items(self.items, ""))
+
+    def test_query_filters_case_insensitively(self):
+        result = _filter_items(self.items, "RESEARCH")
+        self.assertEqual(["researcher", "codex-researcher"], result)
+
+    def test_no_match_returns_empty(self):
+        self.assertEqual([], _filter_items(self.items, "zzz"))
+
+    def test_partial_match(self):
+        result = _filter_items(self.items, "impl")
+        self.assertEqual(["implementer"], result)
+
+    def test_empty_items_returns_empty(self):
+        self.assertEqual([], _filter_items([], "foo"))
+
+
+class TestFilterSelectEmptyItems(unittest.TestCase):
+    def test_returns_none_for_empty_list(self):
+        # No TTY needed — the short-circuit fires before opening tty.
+        result = filter_select([], title="Pick one", tty_path="/dev/null")
+        self.assertIsNone(result)
+
+    def test_returns_none_when_tty_unavailable(self):
+        # /nonexistent is guaranteed to not open.
+        result = filter_select(["a", "b"], tty_path="/nonexistent/tty")
+        self.assertIsNone(result)
+
+
+if __name__ == "__main__":
+    unittest.main()