fix(cli): pin HERMES_KANBAN_BOARD at chat boot to stop subprocess board drift

Without an explicit pin, in-process kanban tools and shelled-out
`hermes kanban …` subprocesses resolve the active board on different
paths: the env var when set, otherwise the global `<root>/kanban/current`
file. When a concurrent session toggles the current-board pointer
mid-turn, the same chat ends up routing tool calls to board A while its
shell calls hit board B, surfacing as phantom "no such task" errors.

Pin the resolved board into env once at `cmd_chat` boot when
HERMES_KANBAN_BOARD isn't already set. Mirrors what the dispatcher does
for spawned workers (kanban_db.py:2622-2623). Idempotent and a no-op
when the env is already pinned by the caller.

Closes #20074

hermes_cli/main.py

@@ -1216,6 +1216,26 @@ def _launch_tui(
     sys.exit(code)
 
 
+def _pin_kanban_board_env() -> None:
+    """Pin the active kanban board into ``HERMES_KANBAN_BOARD`` for the chat session.
+
+    Without this, in-process tools (``kanban_*``) and shelled-out CLI calls
+    (``hermes kanban …``) resolve the board on different paths: the env-pin if
+    set, otherwise the global ``<root>/kanban/current`` file. A concurrent
+    ``hermes kanban boards switch`` from another session can flip the file
+    mid-turn, so the same chat sees its tool calls hit board A while its shell
+    calls hit board B (#20074). Pinning at chat boot mirrors what the
+    dispatcher already does for spawned workers.
+    """
+    if os.environ.get("HERMES_KANBAN_BOARD"):
+        return
+    try:
+        from hermes_cli.kanban_db import get_current_board
+        os.environ["HERMES_KANBAN_BOARD"] = get_current_board()
+    except Exception:
+        pass
+
+
 def cmd_chat(args):
     """Run interactive chat CLI."""
     use_tui = getattr(args, "tui", False) or os.environ.get("HERMES_TUI") == "1"
@@ -1324,6 +1344,8 @@ def cmd_chat(args):
     if getattr(args, "source", None):
         os.environ["HERMES_SESSION_SOURCE"] = args.source
 
+    _pin_kanban_board_env()
+
     if use_tui:
         _launch_tui(
             getattr(args, "resume", None),

tests/hermes_cli/test_pin_kanban_board_env.py

@@ -0,0 +1,54 @@
+"""Tests for `_pin_kanban_board_env` helper invoked by `cmd_chat`.
+
+Regression coverage for #20074: a chat session must export the active kanban
+board into `HERMES_KANBAN_BOARD` at boot so subprocess shell-outs (e.g.
+`hermes kanban …`) inherit the same board the in-process kanban tools resolve.
+Without this, a concurrent `hermes kanban boards switch` from another session
+can flip the global current-board file mid-turn and silently divert the
+shell calls to a different DB.
+"""
+import importlib
+
+
+def test_pin_writes_resolved_board_when_env_unset(monkeypatch):
+    monkeypatch.delenv("HERMES_KANBAN_BOARD", raising=False)
+    main_mod = importlib.import_module("hermes_cli.main")
+
+    import hermes_cli.kanban_db as kdb
+    monkeypatch.setattr(kdb, "get_current_board", lambda: "space")
+
+    main_mod._pin_kanban_board_env()
+
+    assert main_mod.os.environ.get("HERMES_KANBAN_BOARD") == "space"
+
+
+def test_pin_does_not_overwrite_existing_env(monkeypatch):
+    monkeypatch.setenv("HERMES_KANBAN_BOARD", "preset")
+    main_mod = importlib.import_module("hermes_cli.main")
+
+    import hermes_cli.kanban_db as kdb
+
+    def _explode():
+        raise AssertionError("get_current_board must not be called when env is set")
+
+    monkeypatch.setattr(kdb, "get_current_board", _explode)
+
+    main_mod._pin_kanban_board_env()
+
+    assert main_mod.os.environ.get("HERMES_KANBAN_BOARD") == "preset"
+
+
+def test_pin_swallows_resolution_failures(monkeypatch):
+    monkeypatch.delenv("HERMES_KANBAN_BOARD", raising=False)
+    main_mod = importlib.import_module("hermes_cli.main")
+
+    import hermes_cli.kanban_db as kdb
+
+    def _boom():
+        raise RuntimeError("disk gone")
+
+    monkeypatch.setattr(kdb, "get_current_board", _boom)
+
+    main_mod._pin_kanban_board_env()
+
+    assert "HERMES_KANBAN_BOARD" not in main_mod.os.environ