fix(tui): @folder: only yields directories, @file: only yields files

Reported during TUI v2 blitz testing: typing `@folder:` in the composer
pulled up .dockerignore, .env, .gitignore, and every other file in the
cwd alongside the actual directories. The completion loop yielded every
entry regardless of the explicit prefix and auto-rewrote each completion
to @file: vs @folder: based on is_dir — defeating the user's choice.

Also fixed a pre-existing adjacent bug: a bare `@file:` or `@folder:`
(no path) used expanded=="." as both search_dir AND match_prefix,
filtering the list to dotfiles only. When expanded is empty or ".",
search in cwd with no prefix filter.

- want_dir = prefix == "@folder:" drives an explicit is_dir filter
- preserve the typed prefix in completion text instead of rewriting
- three regression tests cover: folder-only, file-only, and the bare-
  prefix case where completions keep the `@folder:` prefix

tests/hermes_cli/test_at_context_completion_filter.py

@@ -0,0 +1,90 @@
+"""Regression test: `@folder:` completion must only surface directories and
+`@file:` must only surface regular files.
+
+Reported during TUI v2 blitz testing: typing `@folder:` showed .dockerignore,
+.env, .gitignore, etc. alongside the actual directories because the path-
+completion branch yielded every entry regardless of the explicit prefix, and
+auto-switched the completion kind based on `is_dir`. That defeated the user's
+explicit choice and rendered the `@folder:` / `@file:` prefixes useless for
+filtering.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Iterable
+
+from hermes_cli.commands import SlashCommandCompleter
+
+
+def _run(tmp_path: Path, word: str) -> list[tuple[str, str]]:
+    (tmp_path / "readme.md").write_text("x")
+    (tmp_path / ".env").write_text("x")
+    (tmp_path / "src").mkdir()
+    (tmp_path / "docs").mkdir()
+
+    completer = SlashCommandCompleter.__new__(SlashCommandCompleter)
+    completions: Iterable = completer._context_completions(word)
+
+    return [(c.text, c.display_meta) for c in completions if c.text.startswith(("@file:", "@folder:"))]
+
+
+def test_at_folder_only_yields_directories(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+
+    texts = [t for t, _ in _run(tmp_path, "@folder:")]
+
+    assert all(t.startswith("@folder:") for t in texts), texts
+    assert any(t == "@folder:src/" for t in texts)
+    assert any(t == "@folder:docs/" for t in texts)
+    assert not any(t == "@folder:readme.md" for t in texts)
+    assert not any(t == "@folder:.env" for t in texts)
+
+
+def test_at_file_only_yields_files(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+
+    texts = [t for t, _ in _run(tmp_path, "@file:")]
+
+    assert all(t.startswith("@file:") for t in texts), texts
+    assert any(t == "@file:readme.md" for t in texts)
+    assert any(t == "@file:.env" for t in texts)
+    assert not any(t == "@file:src/" for t in texts)
+    assert not any(t == "@file:docs/" for t in texts)
+
+
+def test_at_folder_preserves_prefix_on_empty_match(tmp_path, monkeypatch):
+    """User typed `@folder:` (no partial) — completion text must keep the
+    `@folder:` prefix even though the previous implementation auto-rewrote
+    it to `@file:` for non-dir entries.
+    """
+    monkeypatch.chdir(tmp_path)
+
+    texts = [t for t, _ in _run(tmp_path, "@folder:")]
+
+    assert texts, "expected at least one directory completion"
+    for t in texts:
+        assert t.startswith("@folder:"), f"prefix leaked: {t}"
+
+
+def test_at_folder_bare_without_colon_lists_directories(tmp_path, monkeypatch):
+    """Typing `@folder` alone (no colon yet) should surface directories so
+    users don't need to first accept the static `@folder:` hint before
+    seeing what they're picking from.
+    """
+    monkeypatch.chdir(tmp_path)
+
+    texts = [t for t, _ in _run(tmp_path, "@folder")]
+
+    assert any(t == "@folder:src/" for t in texts), texts
+    assert any(t == "@folder:docs/" for t in texts), texts
+    assert not any(t == "@folder:readme.md" for t in texts)
+
+
+def test_at_file_bare_without_colon_lists_files(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+
+    texts = [t for t, _ in _run(tmp_path, "@file")]
+
+    assert any(t == "@file:readme.md" for t in texts), texts
+    assert not any(t == "@file:src/" for t in texts)