Fix shell_and_cli command backstack test: clear history with @clear, keeping prior-session commands in the up-arrow back stack

[Copilot]

The shell_and_cli (windows-latest, 22) job failed on the command backstack shell test — ArrowUp past the startup greeting surfaced @shell setWindowZoomLevel 100 (a command persisted by an earlier serial test) instead of clamping at the expected command.

Error: Wrong back stack command found!
Expected: "@greeting --mock"
Received: "@shell setWindowZoomLevel 100"

Root cause — the serial shell tests share one session, so the dispatcher's persisted display history (every prior run's commands) is replayed into the ArrowUp back stack on startup via ChatPanel.replayHistory(). The command backstack test was asserting against a clean stack and tripped over the leaked prior-session commands.

Per review feedback, prior-session commands should remain in the back stack — replaying them is the intended behavior. So instead of excluding them, the affected test starts from a clean slate by issuing @clear.

Changes

• chatPanel.ts — clear(): also reset the up-arrow back stack (commandHistory / historyIndex). @clear ("reset the chat") now clears the command recall history as well, so it can be used to start from an empty stack.
• hostWindow.spec.ts — command backstack test: issue @clear at the start of the test so the shared-session back stack begins empty, then assert against this test's current-session commands (@history, @help, @config agent). The startup-greeting expectation was removed since @clear clears it along with the prior-session history.

The earlier exclusion-based commits on this branch (skipping replayed entries, @exit filtering, ArrowUp/ArrowDown delta swap) were reverted back to the base branch behavior, which keeps prior-session commands in the back stack.

Net effect: prior-session commands stay recallable in normal use, and the test deterministically walks [@config agent, @help, @history], clamping at @history.

[robgruen]

previous session commands should be in the back-stack of commands

[Copilot]

previous session commands should be in the back-stack of commands

Agreed — reverted the change that excluded prior-session commands from the back stack, so replayed history is seeded into the up-arrow stack again (the base branch already does this). To keep the shared-session command backstack test deterministic I now issue @clear at the start of that test, and made ChatPanel.clear() also reset the back stack so @clear clears the recall history. (3d331ef, latest)