docs(prd): draft PRD 0051 — launch selector TUI

2026-06-04 01:52:29 +00:00
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+# PRD 0051: Launch selector
+
+- **Status:** Draft
+- **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.