fix(cli): sessions export accepts a directory for single-file formats

`hermes sessions export --session-id X <dir>/` crashed with IsADirectoryError
because jsonl/html/trace opened the positional as a file while --help called it
an "output path" and md/qmd really do take a directory. An existing directory
(or one spelled with a trailing separator) now receives a default-named file
(`hermes_session_<id>.<fmt>`), and the help text spells out per-format what
OUTPUT means.

hermes_cli/sessions_cmd.py

@@ -73,6 +73,17 @@ def _export_dir(output) -> Path:
     return Path(output).expanduser() if output and output != "-" else get_hermes_home() / "session-exports"
 
 
+def _output_file_in_dir(output, default_name: str):
+    """Single-file exports accept a directory too (``--help`` calls the positional a path, and md/qmd take
+    one): an existing directory, or one spelled with a trailing separator, means ``<dir>/<default_name>``."""
+    if not output or output == "-":
+        return output
+    if output.endswith(("/", os.sep)) or os.path.isdir(output):
+        os.makedirs(output, exist_ok=True)
+        return os.path.join(output, default_name)
+    return output
+
+
 def _write_output(output, text, summary) -> None:
     """Write to stdout when *output* is empty or ``-``; else to the file + print *summary*."""
     if not output or output == "-":
@@ -375,6 +386,10 @@ def _export_flat(kind, args, collect):
         return
     sessions = collect()
     if sessions is not None:
+        from hermes_cli.session_export import default_save_filename
+        name = (default_save_filename(sessions[0].get("id", ""), args.format) if len(sessions) == 1
+                else f"hermes_sessions.{args.format}")
+        args.output = _output_file_in_dir(args.output, name)
         _write_output(args.output, *render(args, sessions))
 
 
@@ -421,6 +436,7 @@ def _export_trace(db, args, filters):
             if not jsonl:
                 print(f"No transcript to export for session '{ids[0]}'.")
                 return
+            args.output = _output_file_in_dir(args.output, f"{ids[0]}.trace.jsonl")
             _write_output(args.output, jsonl, f"Exported 1 session trace to {args.output}")
         else:
             out_dir = _export_dir(args.output)

hermes_cli/subcommands/sessions.py

@@ -68,9 +68,10 @@ def build_sessions_parser(subparsers, *, cmd_sessions: Callable) -> None:
 
     sessions_export = sessions_subparsers.add_parser(
         "export", help="Export sessions to JSONL, Markdown, or QMD")
-    sessions_export.add_argument("output", nargs="?",
-        help="Output path. JSONL: file path (use - for stdout, required). "
-            "md/qmd: output directory (default: <hermes home>/session-exports)")
+    sessions_export.add_argument("output", nargs="?", metavar="OUTPUT",
+        help="Where to write. jsonl/html/trace: a file path, or a directory (existing, or ending in /) "
+            "to write a default-named file into; - for stdout (jsonl/trace only; jsonl requires OUTPUT). "
+            "md/qmd: a directory, one file per session (default: <hermes home>/session-exports)")
     sessions_export.add_argument(
         "--format", choices=["jsonl", "md", "qmd", "html", "trace"], default="jsonl",
         help="Export format (default: jsonl). 'trace' emits Claude Code JSONL "

tests/hermes_cli/test_sessions_export_output_dir.py

@@ -40,4 +40,4 @@ def test_jsonl_export_to_file_path_is_unchanged(monkeypatch, tmp_path):
     _export(monkeypatch, str(target))
 
     assert json.loads(target.read_text(encoding="utf-8"))["id"] == "sess-123"
-    assert sorted(p.name for p in tmp_path.iterdir()) == ["one.jsonl"]
+    assert target.is_file() and not (tmp_path / "hermes_session_sess-123.jsonl").exists()

website/docs/user-guide/sessions.md

@@ -366,6 +366,10 @@ hermes sessions export telegram-history.jsonl --source telegram
 # Export a single session
 hermes sessions export session.jsonl --session-id 20250305_091523_a1b2c3d4
 
+# Point at a directory (existing, or ending in /) and the file is named for you:
+# ~/exports/hermes_session_20250305_091523_a1b2c3d4.jsonl
+hermes sessions export ~/exports/ --session-id 20250305_091523_a1b2c3d4
+
 # Redact API keys/tokens/credentials from the exported content
 hermes sessions export backup.jsonl --redact
 ```