feat(lsp): add PowerShellEditorServices language server (#55930)

Registers PowerShell (.ps1/.psm1/.psd1) in the LSP server registry,
spawning PowerShellEditorServices over stdio via a pwsh/powershell
host. PSES ships as a GitHub release zip (no npm/go/pip recipe), so it
sits in the manual install tier alongside rust-analyzer and clangd.

The spawn builder resolves the module bundle from (in order) the
lsp.servers.powershell.command override, init bundlePath, the
PSES_BUNDLE_PATH env var, or <HERMES_HOME>/lsp/PowerShellEditorServices,
then launches Start-EditorServices.ps1 -Stdio with a non-interactive,
no-profile host. hermes lsp status/list report it as manual-only until
pwsh is present.

Docs and tests included.

tests/agent/lsp/test_powershell_server.py

@@ -0,0 +1,114 @@
+"""Tests for the PowerShellEditorServices (PSES) server registration.
+
+PSES is unusual among the registry entries: it's a PowerShell module
+bundle (GitHub release zip) driven by a ``pwsh`` bootstrap script, not a
+single binary on PATH. These tests cover the registry wiring plus the
+two-prerequisite spawn logic (pwsh host + module bundle).
+"""
+from __future__ import annotations
+
+import os
+
+import agent.lsp.servers as srv
+from agent.lsp.install import detect_status
+from agent.lsp.servers import (
+    ServerContext,
+    find_server_for_file,
+    language_id_for,
+)
+
+
+def test_powershell_extensions_route_to_pses():
+    for ext in ("script.ps1", "module.psm1", "manifest.psd1"):
+        s = find_server_for_file(ext)
+        assert s is not None, ext
+        assert s.server_id == "powershell"
+
+
+def test_powershell_language_ids():
+    assert language_id_for("a.ps1") == "powershell"
+    assert language_id_for("a.psm1") == "powershell"
+    assert language_id_for("a.psd1") == "powershell"
+
+
+def test_powershell_install_status_is_manual_tier():
+    # PSES has no npm/go/pip recipe; it's manual-only (like rust-analyzer).
+    # When pwsh isn't on PATH the status is manual-only, not "missing".
+    status = detect_status("powershell")
+    assert status in {"manual-only", "installed"}
+
+
+def test_spawn_skips_when_pwsh_missing(monkeypatch, tmp_path):
+    monkeypatch.setattr(srv, "_which", lambda *names: None)
+    ctx = ServerContext(workspace_root=str(tmp_path), install_strategy="manual")
+    assert srv._spawn_powershell_es(str(tmp_path), ctx) is None
+
+
+def test_spawn_skips_when_bundle_missing(monkeypatch, tmp_path):
+    # pwsh present, but no bundle anywhere.
+    monkeypatch.setattr(srv, "_which", lambda *names: "/usr/bin/pwsh")
+    monkeypatch.delenv("PSES_BUNDLE_PATH", raising=False)
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path / "hermes_home"))
+    ctx = ServerContext(workspace_root=str(tmp_path), install_strategy="manual")
+    assert srv._spawn_powershell_es(str(tmp_path), ctx) is None
+
+
+def _make_fake_bundle(root) -> str:
+    bundle = root / "PowerShellEditorServices"
+    inner = bundle / "PowerShellEditorServices"
+    inner.mkdir(parents=True)
+    (inner / "Start-EditorServices.ps1").write_text("# fake")
+    return str(bundle)
+
+
+def test_spawn_builds_command_with_bundle_via_env(monkeypatch, tmp_path):
+    monkeypatch.setattr(srv, "_which", lambda *names: "/usr/bin/pwsh")
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path / "hermes_home"))
+    bundle = _make_fake_bundle(tmp_path)
+    monkeypatch.setenv("PSES_BUNDLE_PATH", bundle)
+
+    ctx = ServerContext(workspace_root=str(tmp_path), install_strategy="manual")
+    spec = srv._spawn_powershell_es(str(tmp_path), ctx)
+    assert spec is not None
+    assert spec.command[0] == "/usr/bin/pwsh"
+    assert "-Stdio" in spec.command[-1]
+    assert "Start-EditorServices.ps1" in spec.command[-1]
+    assert bundle in spec.command[-1]
+    # -NonInteractive / -NoProfile keep the host from hanging on a prompt.
+    assert "-NonInteractive" in spec.command
+    assert "-NoProfile" in spec.command
+
+
+def test_spawn_prefers_command_override_bundle(monkeypatch, tmp_path):
+    monkeypatch.setattr(srv, "_which", lambda *names: "/usr/bin/pwsh")
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path / "hermes_home"))
+    monkeypatch.delenv("PSES_BUNDLE_PATH", raising=False)
+    bundle = _make_fake_bundle(tmp_path)
+
+    ctx = ServerContext(
+        workspace_root=str(tmp_path),
+        install_strategy="manual",
+        binary_overrides={"powershell": [bundle]},
+    )
+    spec = srv._spawn_powershell_es(str(tmp_path), ctx)
+    assert spec is not None
+    assert bundle in spec.command[-1]
+
+
+def test_bundle_path_init_override_not_leaked_into_init_options(monkeypatch, tmp_path):
+    monkeypatch.setattr(srv, "_which", lambda *names: "/usr/bin/pwsh")
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path / "hermes_home"))
+    monkeypatch.delenv("PSES_BUNDLE_PATH", raising=False)
+    bundle = _make_fake_bundle(tmp_path)
+
+    ctx = ServerContext(
+        workspace_root=str(tmp_path),
+        install_strategy="manual",
+        init_overrides={"powershell": {"bundlePath": bundle, "foo": "bar"}},
+    )
+    spec = srv._spawn_powershell_es(str(tmp_path), ctx)
+    assert spec is not None
+    # bundlePath is a Hermes-internal resolution key — it must not be sent
+    # to the server as an LSP initializationOption.
+    assert "bundlePath" not in spec.initialization_options
+    assert spec.initialization_options.get("foo") == "bar"