diff --git a/src/hqt/cli.py b/src/hqt/cli.py
index 6460e94..84625fb 100644
--- a/src/hqt/cli.py
+++ b/src/hqt/cli.py
@@ -1,5 +1,6 @@
 import logging
 import os
+import shlex
 import shutil
 import subprocess
 import sys
@@ -128,6 +129,114 @@ def doctor():
         click.echo("bubblewrap: ✗ not found — sandboxed sessions unavailable")
 
 
+def _build_session_service():
+    """Wire a SessionService the same way HqtApp.on_mount does (for CLI use).
+
+    Mirrors on_mount's DB + tmux wiring, including seeding harness rows, but
+    deliberately omits apply_theme — a one-off CLI call must not re-theme the
+    session's status bar.
+    """
+    from hqt.config import get_settings
+    from hqt.db.engine import ensure_db, get_engine, get_session_factory
+    from hqt.harnesses.registry import discover_harnesses, ensure_harnesses_in_db
+    from hqt.sessions.service import SessionService
+    from hqt.tmux.manager import TmuxManager
+    from hqt.tmux.runner import TmuxRunner
+
+    settings = get_settings()
+    ensure_db(settings)
+    factory = get_session_factory(get_engine(settings))
+    with factory() as db:
+        ensure_harnesses_in_db(db)
+    runner = TmuxRunner(settings.tmux_path, settings.tui_session_name)
+    return SessionService(factory, TmuxManager(runner), discover_harnesses())
+
+
+@main.command(name="tool")
+@click.argument("tool")
+@click.argument("window")
+def tool_cmd(tool, window):
+    """Run TOOL for the session in tmux WINDOW.
+
+    TOOL is nvim/lazygit/shell (opens a styled tool window) or "clone" (a fresh
+    harness with the same project + model). WINDOW is the tmux window name (the
+    hqt-<id> key, e.g. from #{window_name}).
+    """
+    import asyncio
+
+    from hqt.errors import ServiceError
+
+    svc = _build_session_service()
+    try:
+        if tool == "clone":
+            asyncio.run(svc.clone_session_for_window(window))
+        else:
+            asyncio.run(svc.open_tool_window_for_window(window, tool))
+    except ServiceError as err:
+        click.echo(str(err), err=True)
+        raise SystemExit(1)
+
+
+PALETTE_ENTRIES = ["nvim", "lazygit", "shell", "clone"]
+
+# fzf colors matching the Catppuccin Frappé status bar / the Alt+o switcher.
+_PALETTE_FZF_COLORS = (
+    "bg:#292c3c,bg+:#414559,fg:#c6d0f5,fg+:#c6d0f5,hl:#ef9f76,hl+:#ef9f76,"
+    "pointer:#ef9f76,prompt:#8caaee,info:#838ba7,border:#838ba7"
+)
+
+
+def _palette_popup_command(window: str) -> str:
+    """Shell pipeline for the fzf popup; `window` is baked in as a literal.
+
+    display-popup does NOT format-expand its command, so the window name must be
+    concrete here (run-shell already expanded #{window_name} before `hqt palette`
+    ran). The selected entry runs `hqt tool <choice> <window>`.
+    """
+    entries = "\\n".join(PALETTE_ENTRIES) + "\\n"
+    return (
+        f"printf '{entries}' | "
+        f"fzf --reverse --no-info --prompt='tool  ' --pointer='▌' "
+        f"--color='{_PALETTE_FZF_COLORS}' | "
+        f"xargs -r -I{{}} hqt tool {{}} {shlex.quote(window)}"
+    )
+
+
+@main.command(name="palette")
+@click.argument("window")
+def palette_cmd(window):
+    """Pop an fzf tool palette for the session in tmux WINDOW (bound to M-p)."""
+    from hqt.config import get_settings
+
+    settings = get_settings()
+    svc = _build_session_service()
+    if svc.session_id_for_window(window) is None:
+        subprocess.run(
+            [
+                settings.tmux_path,
+                "display-message",
+                "hqt: open the tool palette from a harness window",
+            ]
+        )
+        return
+    subprocess.run(
+        [
+            settings.tmux_path,
+            "display-popup",
+            "-E",
+            "-w",
+            "40%",
+            "-h",
+            "30%",
+            "-T",
+            " open tool ",
+            "-S",
+            "fg=#838ba7",
+            _palette_popup_command(window),
+        ]
+    )
+
+
 @main.command(name="list")
 def list_cmd():
     """List projects and sessions."""
diff --git a/src/hqt/sessions/service.py b/src/hqt/sessions/service.py
index 76b26bf..f2488da 100644
--- a/src/hqt/sessions/service.py
+++ b/src/hqt/sessions/service.py
@@ -2,6 +2,7 @@ import asyncio
 import contextlib
 import json
 import logging
+import shutil
 import time
 from collections.abc import Mapping, Sequence
 from dataclasses import dataclass
@@ -19,6 +20,7 @@ from hqt.git.worktree import WorktreeState
 from hqt.harnesses.base import HarnessConfigurator, SpawnConfig
 from hqt.sandbox import Bind, SandboxPolicy
 from hqt.status import window_label
+from hqt.tools import TOOLS
 from hqt.tmux.manager import SpawnRequest, TmuxManager
 from hqt.tmux.runner import WindowInfo
 
@@ -489,6 +491,85 @@ class SessionService:
                     )
         return True, ""
 
+    def session_id_for_window(self, window_name: str) -> int | None:
+        """Resolve a tmux window name to its active hqt session id, or None.
+
+        None means the window is not an hqt session window (a tool window, the
+        TUI home window, or an unrelated tmux window).
+        """
+        with self.factory() as db:
+            sess = (
+                db.query(Session)
+                .filter_by(tmux_session_name=window_name, archived=False)
+                .first()
+            )
+            return sess.id if sess else None
+
+    async def open_tool_window(self, session_id: int, tool: str) -> str | None:
+        """Open a tool (nvim/lazygit/shell) in a new styled window for a session.
+
+        Spawns at the next free index in the session's project directory and
+        switches to it. The window is NOT a tracked session. Raises ServiceError
+        for an unknown tool, a missing binary, or a missing session/project.
+        Returns the new window_id, or None if the tmux spawn fails.
+        """
+        log.info("Opening tool window: session=%s tool=%s", session_id, tool)
+        spec = TOOLS.get(tool)
+        if spec is None:
+            raise ServiceError(f"Unknown tool '{tool}'")
+        if spec.command and shutil.which(spec.command[0]) is None:
+            raise ServiceError(f"{spec.command[0]} not found on PATH")
+        with self.factory() as db:
+            sess = db.get(Session, session_id)
+            if sess is None:
+                raise ServiceError("Session not found")
+            project = db.get(Project, sess.project_id)
+            if project is None:
+                raise ServiceError(f"Project {sess.project_id} no longer exists")
+            cwd = project.path
+            label = f"{spec.label} · {project.name}"
+        return await self.tmux.open_aux_window(spec.label, cwd, spec.command, label)
+
+    async def open_tool_window_for_window(
+        self, window_name: str, tool: str
+    ) -> str | None:
+        """Open a tool window for the session identified by its tmux window name.
+
+        Used by the `hqt tool` CLI (the tmux binding passes #{window_name}).
+        Raises ServiceError if the name is not an active hqt session window.
+        """
+        session_id = self.session_id_for_window(window_name)
+        if session_id is None:
+            raise ServiceError(f"{window_name!r} is not an hqt session window")
+        return await self.open_tool_window(session_id, tool)
+
+    async def clone_session_for_window(
+        self, window_name: str
+    ) -> "CreateSessionResult":
+        """Open a fresh harness session cloning the one in `window_name`.
+
+        Same project, harness, and model as the source session, but a brand-new
+        conversation (a new hqt-<id> window at the next index). Raises
+        ServiceError if `window_name` is not an active hqt session window — so
+        invoking clone from a tool window (nvim/shell) or the TUI is a clean
+        no-op.
+        """
+        with self.factory() as db:
+            sess = (
+                db.query(Session)
+                .options(selectinload(Session.harness))
+                .filter_by(tmux_session_name=window_name, archived=False)
+                .first()
+            )
+            if sess is None:
+                raise ServiceError(f"{window_name!r} is not an hqt session window")
+            project_id = sess.project_id
+            harness_name = sess.harness.name
+            model = sess.model
+        return await self.create_session(
+            project_id, harness_name, nickname=None, model=model
+        )
+
     async def stop_session(self, session_id: int) -> None:
         with self.factory() as db:
             sess = db.get(Session, session_id)
diff --git a/src/hqt/tmux/manager.py b/src/hqt/tmux/manager.py
index e589ae1..bf43a81 100644
--- a/src/hqt/tmux/manager.py
+++ b/src/hqt/tmux/manager.py
@@ -128,3 +128,12 @@ class TmuxManager:
     async def reset_window_indexes(self, home_window: str) -> bool:
         """Compact tmux window indexes while keeping the home window at 0."""
         return await self.runner.reset_window_indexes(home_window)
+
+    async def open_aux_window(
+        self, name: str, cwd: str, command: list[str], label: str
+    ) -> str | None:
+        """Open a styled tool window (non-session) and switch to it.
+
+        Returns the new window_id, or None on failure.
+        """
+        return await self.runner.new_aux_window(name, cwd, command, label)
diff --git a/src/hqt/tmux/runner.py b/src/hqt/tmux/runner.py
index c90152d..a237ea6 100644
--- a/src/hqt/tmux/runner.py
+++ b/src/hqt/tmux/runner.py
@@ -1,5 +1,6 @@
 import asyncio
 import logging
+import shlex
 from dataclasses import dataclass
 
 log = logging.getLogger(__name__)
@@ -422,6 +423,77 @@ class TmuxRunner:
 
         return window_id
 
+    async def new_aux_window(
+        self, name: str, cwd: str, command: list[str], label: str
+    ) -> str | None:
+        """Create an auxiliary (non-session) tool window and switch to it.
+
+        Appends at the next free index, then styles by window_id — not name — so
+        duplicate names (tool windows are spawned fresh every time) stay
+        unambiguous. Deliberately does NOT set remain-on-exit: the window closes
+        when the tool exits (a quit shell closes its window too). The window is
+        never tracked by hqt; it lives purely as a tmux window.
+
+        Returns the window_id, or None on failure (the half-created window is
+        cleaned up).
+        """
+        idx = await self._next_window_index()
+        args = [
+            "new-window",
+            "-t",
+            f"{self.session_name}:{idx}",
+            "-n",
+            name,
+            "-c",
+            cwd,
+            "-P",
+            "-F",
+            "#{window_id}",
+        ]
+        if command:
+            args.append(shlex.join(command))
+        rc, stdout, err = await self._exec(*args)
+        if rc != 0:
+            log.error("new-window (aux) failed: %s", err)
+            return None
+        window_id = stdout.strip()
+
+        # Style by window_id: automatic-rename + allow-rename off (nvim/lazygit
+        # emit OSC title sequences that would otherwise scramble the label), the
+        # @hqt_label, then the Frappé per-window theme — one atomic invocation
+        # (";" argv separators). Mirrors new_window's window-option setup.
+        rc, _, err = await self._exec(
+            "set-option",
+            "-w",
+            "-t",
+            window_id,
+            "automatic-rename",
+            "off",
+            ";",
+            "set-option",
+            "-w",
+            "-t",
+            window_id,
+            "allow-rename",
+            "off",
+            ";",
+            "set-option",
+            "-w",
+            "-t",
+            window_id,
+            "@hqt_label",
+            label,
+            ";",
+            *_window_theme_args(window_id),
+        )
+        if rc != 0:
+            log.error("set-option (aux window) failed for %s: %s", name, err)
+            await self._exec("kill-window", "-t", window_id)
+            return None
+
+        await self._exec("select-window", "-t", window_id)
+        return window_id
+
     async def has_window(self, window_name: str) -> bool:
         """Check if a window with this name exists."""
         rc, stdout, _ = await self._exec(
diff --git a/src/hqt/tools.py b/src/hqt/tools.py
new file mode 100644
index 0000000..109ecae
--- /dev/null
+++ b/src/hqt/tools.py
@@ -0,0 +1,28 @@
+"""Tools that can be opened in their own tmux window for a session's project.
+
+A tool window is NOT an hqt session: hqt spawns and styles it, then forgets it.
+It lives purely as a tmux window until the tool exits. (``clone`` is handled
+separately in the service — it creates a real session, not an aux window.)
+"""
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class Tool:
+    """How to open a tool in its own window.
+
+    ``label`` is the base ``@hqt_label`` text (the project name is appended per
+    spawn). ``command`` is the argv to run; an empty list means "use tmux's
+    default shell" (a plain interactive shell).
+    """
+
+    label: str
+    command: list[str]
+
+
+TOOLS: dict[str, Tool] = {
+    "nvim": Tool(label="nvim", command=["nvim"]),
+    "lazygit": Tool(label="lazygit", command=["lazygit"]),
+    "shell": Tool(label="shell", command=[]),
+}
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 377c809..c31b6e0 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -2,9 +2,8 @@ from unittest.mock import patch
 
 from click.testing import CliRunner
 
-from hqt import cli as cli_module
-from hqt import sandbox
-from hqt.cli import main
+from hqt import cli, sandbox
+from hqt.config import Settings
 
 
 def _which(found: set[str]):
@@ -16,10 +15,10 @@ def test_doctor_reports_bwrap_present():
     # tmux is discovered via cli.shutil.which; bwrap availability comes from the
     # shared sandbox.is_available() helper (the single source of truth).
     with (
-        patch.object(cli_module.shutil, "which", side_effect=_which({"tmux", "bwrap"})),
+        patch.object(cli.shutil, "which", side_effect=_which({"tmux", "bwrap"})),
         patch.object(sandbox, "is_available", return_value=True),
     ):
-        result = CliRunner().invoke(main, ["doctor"])
+        result = CliRunner().invoke(cli.main, ["doctor"])
     assert result.exit_code == 0
     assert "bubblewrap: ✓" in result.output
 
@@ -27,9 +26,114 @@ def test_doctor_reports_bwrap_present():
 def test_doctor_reports_bwrap_missing():
     """Test that doctor reports bubblewrap as missing when not present."""
     with (
-        patch.object(cli_module.shutil, "which", side_effect=_which({"tmux"})),
+        patch.object(cli.shutil, "which", side_effect=_which({"tmux"})),
         patch.object(sandbox, "is_available", return_value=False),
     ):
-        result = CliRunner().invoke(main, ["doctor"])
+        result = CliRunner().invoke(cli.main, ["doctor"])
     assert result.exit_code == 0
     assert "bubblewrap: ✗" in result.output
+
+
+def test_tool_cmd_opens_tool_window(monkeypatch, tmp_path):
+    monkeypatch.setattr(
+        "hqt.config.get_settings", lambda: Settings(db_path=tmp_path / "t.db")
+    )
+    calls = {}
+
+    async def fake_for_window(self, window, tool):
+        calls["tool"] = (window, tool)
+        return "@9"
+
+    monkeypatch.setattr(
+        "hqt.sessions.service.SessionService.open_tool_window_for_window",
+        fake_for_window,
+    )
+
+    result = CliRunner().invoke(cli.main, ["tool", "lazygit", "hqt-5"])
+
+    assert result.exit_code == 0, result.output
+    assert calls["tool"] == ("hqt-5", "lazygit")
+
+
+def test_tool_cmd_clone_dispatches_to_clone(monkeypatch, tmp_path):
+    monkeypatch.setattr(
+        "hqt.config.get_settings", lambda: Settings(db_path=tmp_path / "t.db")
+    )
+    calls = {}
+
+    async def fake_clone(self, window):
+        calls["clone"] = window
+        return "RESULT"
+
+    monkeypatch.setattr(
+        "hqt.sessions.service.SessionService.clone_session_for_window", fake_clone
+    )
+
+    result = CliRunner().invoke(cli.main, ["tool", "clone", "hqt-5"])
+
+    assert result.exit_code == 0, result.output
+    assert calls["clone"] == "hqt-5"
+
+
+def test_tool_cmd_reports_service_error(monkeypatch, tmp_path):
+    from hqt.errors import ServiceError
+
+    monkeypatch.setattr(
+        "hqt.config.get_settings", lambda: Settings(db_path=tmp_path / "t.db")
+    )
+
+    async def boom(self, window, tool):
+        raise ServiceError("'hqt-5' is not an hqt session window")
+
+    monkeypatch.setattr(
+        "hqt.sessions.service.SessionService.open_tool_window_for_window", boom
+    )
+
+    result = CliRunner().invoke(cli.main, ["tool", "nvim", "hqt-5"])
+
+    assert result.exit_code == 1
+    assert "not an hqt session window" in result.output
+
+
+def test_palette_cmd_shows_popup_for_session_window(monkeypatch, tmp_path):
+    monkeypatch.setattr(
+        "hqt.config.get_settings", lambda: Settings(db_path=tmp_path / "t.db")
+    )
+    monkeypatch.setattr(
+        "hqt.sessions.service.SessionService.session_id_for_window",
+        lambda self, window: 5,
+    )
+    runs = []
+    monkeypatch.setattr(cli.subprocess, "run", lambda argv, **kw: runs.append(argv))
+
+    result = CliRunner().invoke(cli.main, ["palette", "hqt-5"])
+
+    assert result.exit_code == 0, result.output
+    assert len(runs) == 1
+    argv = runs[0]
+    assert "display-popup" in argv
+    popup_cmd = argv[-1]
+    assert "fzf" in popup_cmd
+    assert "nvim" in popup_cmd and "clone" in popup_cmd
+    # the window is baked into the command for `hqt tool {} <window>`
+    assert "hqt-5" in popup_cmd
+
+
+def test_palette_cmd_hints_for_non_session_window(monkeypatch, tmp_path):
+    monkeypatch.setattr(
+        "hqt.config.get_settings", lambda: Settings(db_path=tmp_path / "t.db")
+    )
+    monkeypatch.setattr(
+        "hqt.sessions.service.SessionService.session_id_for_window",
+        lambda self, window: None,
+    )
+    runs = []
+    monkeypatch.setattr(cli.subprocess, "run", lambda argv, **kw: runs.append(argv))
+
+    result = CliRunner().invoke(cli.main, ["palette", "nvim"])
+
+    assert result.exit_code == 0, result.output
+    assert len(runs) == 1
+    argv = runs[0]
+    assert "display-message" in argv
+    assert "display-popup" not in argv
diff --git a/tests/test_sessions.py b/tests/test_sessions.py
index 9c41477..5b5292e 100644
--- a/tests/test_sessions.py
+++ b/tests/test_sessions.py
@@ -2010,3 +2010,121 @@ async def test_sandboxed_worktree_binds_repo_git_dir(
         )
     binds = mock_wrap.call_args.args[3]
     assert Bind(Path("/tmp/myproj/.git"), writable=True) in binds
+
+
+# ---------------------------------------------------------------------------
+# Task 4: SessionService tool-window methods
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_open_tool_window_spawns_styled_window(service, db, tmux, monkeypatch):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    monkeypatch.setattr("hqt.sessions.service.shutil.which", lambda b: "/usr/bin/" + b)
+    tmux.open_aux_window = AsyncMock(return_value="@5")
+
+    wid = await service.open_tool_window(1, "lazygit")
+
+    assert wid == "@5"
+    tmux.open_aux_window.assert_awaited_once_with(
+        "lazygit", "/tmp/myproj", ["lazygit"], "lazygit · myproj"
+    )
+
+
+@pytest.mark.asyncio
+async def test_open_tool_window_shell_skips_which_check(service, db, tmux, monkeypatch):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    monkeypatch.setattr("hqt.sessions.service.shutil.which", lambda b: None)
+    tmux.open_aux_window = AsyncMock(return_value="@3")
+
+    wid = await service.open_tool_window(1, "shell")
+
+    assert wid == "@3"
+    tmux.open_aux_window.assert_awaited_once_with(
+        "shell", "/tmp/myproj", [], "shell · myproj"
+    )
+
+
+@pytest.mark.asyncio
+async def test_open_tool_window_unknown_tool_raises(service):
+    with pytest.raises(ServiceError):
+        await service.open_tool_window(1, "emacs")
+
+
+@pytest.mark.asyncio
+async def test_open_tool_window_missing_binary_raises(service, db, monkeypatch):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    monkeypatch.setattr("hqt.sessions.service.shutil.which", lambda b: None)
+    with pytest.raises(ServiceError):
+        await service.open_tool_window(1, "lazygit")
+
+
+@pytest.mark.asyncio
+async def test_open_tool_window_unknown_session_raises(service, monkeypatch):
+    monkeypatch.setattr("hqt.sessions.service.shutil.which", lambda b: "/usr/bin/" + b)
+    with pytest.raises(ServiceError):
+        await service.open_tool_window(999, "nvim")
+
+
+@pytest.mark.asyncio
+async def test_session_id_for_window_resolves_and_misses(service, db):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    assert service.session_id_for_window("hqt-1") == 1
+    assert service.session_id_for_window("not-an-hqt-window") is None
+
+
+@pytest.mark.asyncio
+async def test_open_tool_window_for_window_resolves_by_name(
+    service, db, tmux, monkeypatch
+):
+    await service.create_session(project_id=1, harness_name="claude-code")
+    monkeypatch.setattr("hqt.sessions.service.shutil.which", lambda b: "/usr/bin/" + b)
+    tmux.open_aux_window = AsyncMock(return_value="@2")
+
+    wid = await service.open_tool_window_for_window("hqt-1", "nvim")
+
+    assert wid == "@2"
+    tmux.open_aux_window.assert_awaited_once_with(
+        "nvim", "/tmp/myproj", ["nvim"], "nvim · myproj"
+    )
+
+
+@pytest.mark.asyncio
+async def test_open_tool_window_for_window_unknown_window_raises(service):
+    with pytest.raises(ServiceError):
+        await service.open_tool_window_for_window("not-an-hqt-window", "nvim")
+
+
+# ---------------------------------------------------------------------------
+# Task 5: clone_session_for_window
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_clone_session_for_window_reuses_project_harness_model(
+    service, db, monkeypatch
+):
+    await service.create_session(
+        project_id=1, harness_name="claude-code", nickname="orig", model="opus"
+    )
+    captured = {}
+
+    async def fake_create(
+        project_id, harness_name, nickname=None, model=None, worktree_branch=None
+    ):
+        captured["args"] = (project_id, harness_name, nickname, model)
+        return "SENTINEL"
+
+    monkeypatch.setattr(service, "create_session", fake_create)
+
+    result = await service.clone_session_for_window("hqt-1")
+
+    assert result == "SENTINEL"
+    # Same project + harness + model; a fresh sibling, so no nickname.
+    assert captured["args"] == (1, "claude-code", None, "opus")
+
+
+@pytest.mark.asyncio
+async def test_clone_session_for_window_unknown_window_raises(service):
+    with pytest.raises(ServiceError):
+        await service.clone_session_for_window("not-an-hqt-window")
diff --git a/tests/test_tmux.py b/tests/test_tmux.py
index 88fb6a4..c365de9 100644
--- a/tests/test_tmux.py
+++ b/tests/test_tmux.py
@@ -1208,3 +1208,90 @@ async def test_poll_info_empty_names(runner):
     result = await mgr.poll_info([])
     assert result == {}
     assert runner._exec.call_count == 1
+
+
+# ---------------------------------------------------------------------------
+# Task 2: new_aux_window — styled tool windows (never tracked)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_new_aux_window_spawns_styles_and_selects(runner):
+    runner._exec.side_effect = [
+        (0, "0\n", ""),   # _next_window_index: indices [0] -> next index 1
+        (0, "@7\n", ""),  # new-window -P -F '#{window_id}'
+        (0, "", ""),      # set-option (automatic-rename + allow-rename + @hqt_label + theme)
+        (0, "", ""),      # select-window
+    ]
+    wid = await runner.new_aux_window("lazygit", "/proj", ["lazygit"], "lazygit · proj")
+    assert wid == "@7"
+
+    calls = runner._exec.call_args_list
+    # new-window: next free index, name, cwd, print window_id, then the command.
+    assert calls[1].args == (
+        "new-window", "-t", "hqt-main:1", "-n", "lazygit",
+        "-c", "/proj", "-P", "-F", "#{window_id}", "lazygit",
+    )
+    # post-creation options target the window_id and NEVER set remain-on-exit.
+    assert calls[2].args[:6] == (
+        "set-option", "-w", "-t", "@7", "automatic-rename", "off",
+    )
+    # allow-rename off too, so nvim/lazygit OSC titles can't scramble the label.
+    assert "allow-rename" in calls[2].args
+    assert "@hqt_label" in calls[2].args
+    assert "lazygit · proj" in calls[2].args
+    assert "remain-on-exit" not in calls[2].args
+    # switch to it.
+    assert calls[3].args == ("select-window", "-t", "@7")
+
+
+@pytest.mark.asyncio
+async def test_new_aux_window_shell_omits_command_arg(runner):
+    runner._exec.side_effect = [
+        (0, "2\n", ""),   # indices [2] -> next index 3
+        (0, "@9\n", ""),
+        (0, "", ""),
+        (0, "", ""),
+    ]
+    wid = await runner.new_aux_window("shell", "/proj", [], "shell · proj")
+    assert wid == "@9"
+    calls = runner._exec.call_args_list
+    assert calls[1].args == (
+        "new-window", "-t", "hqt-main:3", "-n", "shell",
+        "-c", "/proj", "-P", "-F", "#{window_id}",
+    )
+
+
+@pytest.mark.asyncio
+async def test_new_aux_window_returns_none_when_new_window_fails(runner):
+    runner._exec.side_effect = [
+        (0, "0\n", ""),    # next index
+        (1, "", "boom"),   # new-window fails
+    ]
+    wid = await runner.new_aux_window("nvim", "/p", ["nvim"], "nvim · p")
+    assert wid is None
+
+
+@pytest.mark.asyncio
+async def test_new_aux_window_kills_window_when_set_option_fails(runner):
+    runner._exec.side_effect = [
+        (0, "0\n", ""),    # _next_window_index
+        (0, "@7\n", ""),   # new-window -> window_id @7
+        (1, "", "nope"),   # set-option fails
+        (0, "", ""),       # kill-window cleanup
+    ]
+    wid = await runner.new_aux_window("nvim", "/p", ["nvim"], "nvim · p")
+    assert wid is None
+    # the half-built window must be cleaned up by id.
+    assert runner._exec.call_args_list[-1].args == ("kill-window", "-t", "@7")
+
+
+@pytest.mark.asyncio
+async def test_manager_open_aux_window_delegates(runner):
+    from unittest.mock import AsyncMock
+
+    runner.new_aux_window = AsyncMock(return_value="@4")
+    mgr = TmuxManager(runner)
+    wid = await mgr.open_aux_window("nvim", "/p", ["nvim"], "nvim · p")
+    assert wid == "@4"
+    runner.new_aux_window.assert_awaited_once_with("nvim", "/p", ["nvim"], "nvim · p")
diff --git a/tests/test_tools.py b/tests/test_tools.py
new file mode 100644
index 0000000..51fcea8
--- /dev/null
+++ b/tests/test_tools.py
@@ -0,0 +1,24 @@
+from hqt.tools import TOOLS, Tool
+
+
+def test_registry_has_the_three_tools():
+    assert set(TOOLS) == {"nvim", "lazygit", "shell"}
+
+
+def test_each_entry_is_a_tool():
+    assert all(isinstance(t, Tool) for t in TOOLS.values())
+
+
+def test_nvim_and_lazygit_have_commands():
+    assert TOOLS["nvim"].command == ["nvim"]
+    assert TOOLS["lazygit"].command == ["lazygit"]
+
+
+def test_shell_has_empty_command_meaning_default_shell():
+    assert TOOLS["shell"].command == []
+
+
+def test_labels_are_the_bare_tool_names():
+    assert TOOLS["nvim"].label == "nvim"
+    assert TOOLS["lazygit"].label == "lazygit"
+    assert TOOLS["shell"].label == "shell"