fix(cli): ignore stale HERMES_TUI_RESUME env

HERMES_TUI_RESUME is an internal env var the Python wrapper exports to hand
a session ID off to the Ink TUI. Because _launch_tui started from
os.environ.copy(), any exported/stale value in the user's shell leaked
through — so plain `hermes --tui` would try to resume a missing session
and leave the UI at 'error: session not found' with no live session.

Drop HERMES_TUI_RESUME from the env before conditionally re-setting it
from the argparse-resolved resume_session_id. Tests cover both the drop
path and the set-from-arg path.

Salvage of #28080 by @noctilust.

hermes_cli/main.py

@@ -1278,6 +1278,14 @@ def _launch_tui(
     if "--expose-gc" not in _tokens:
         _tokens.append("--expose-gc")
     env["NODE_OPTIONS"] = " ".join(_tokens)
+    # HERMES_TUI_RESUME is an internal hand-off from the Python wrapper to the
+    # Ink app.  Because we start from os.environ.copy(), an exported/stale value
+    # in the user's shell would otherwise make a plain `hermes --tui` try to
+    # resume a non-existent session and leave the UI at "error: session not
+    # found" with no live session.  Only forward a resume id that argparse
+    # resolved for this invocation; direct `node ui-tui/dist/entry.js` users can
+    # still set HERMES_TUI_RESUME themselves.
+    env.pop("HERMES_TUI_RESUME", None)
     if resume_session_id:
         env["HERMES_TUI_RESUME"] = resume_session_id
 

tests/hermes_cli/test_tui_resume_flow.py

@@ -541,6 +541,48 @@ def test_launch_tui_exit_code_42_relaunches_update(monkeypatch, main_mod):
     mock_relaunch.assert_called_once_with(["update"], preserve_inherited=False)
 
 
+def test_launch_tui_drops_stale_resume_env_without_resume_arg(monkeypatch, main_mod):
+    captured = {}
+
+    monkeypatch.setenv("HERMES_TUI_RESUME", "stale-missing-session")
+    monkeypatch.setattr(
+        main_mod,
+        "_make_tui_argv",
+        lambda tui_dir, tui_dev: (["node", "dist/entry.js"], Path(".")),
+    )
+    monkeypatch.setattr(
+        main_mod.subprocess,
+        "call",
+        lambda argv, cwd=None, env=None: captured.update({"env": env}) or 1,
+    )
+
+    with pytest.raises(SystemExit):
+        main_mod._launch_tui()
+
+    assert "HERMES_TUI_RESUME" not in captured["env"]
+
+
+def test_launch_tui_sets_resume_env_from_resume_arg(monkeypatch, main_mod):
+    captured = {}
+
+    monkeypatch.setenv("HERMES_TUI_RESUME", "stale-missing-session")
+    monkeypatch.setattr(
+        main_mod,
+        "_make_tui_argv",
+        lambda tui_dir, tui_dev: (["node", "dist/entry.js"], Path(".")),
+    )
+    monkeypatch.setattr(
+        main_mod.subprocess,
+        "call",
+        lambda argv, cwd=None, env=None: captured.update({"env": env}) or 1,
+    )
+
+    with pytest.raises(SystemExit):
+        main_mod._launch_tui(resume_session_id="20260518_000000_goodid")
+
+    assert captured["env"]["HERMES_TUI_RESUME"] == "20260518_000000_goodid"
+
+
 def test_make_tui_argv_dev_prebuilds_hermes_ink(monkeypatch, main_mod, tmp_path):
     tui_dir = tmp_path / "ui-tui"
     tsx = tui_dir / "node_modules" / ".bin" / "tsx"