Reported during TUI v2 blitz retest: `/history` in the TUI only shows
prompts from non-TUI Hermes runs and can't scroll the window. Root
cause is the slash-worker subprocess: it's a detached HermesCLI that
never sees the TUI's turns, so its `conversation_history` starts empty
and `show_history` surfaces whatever was persisted from earlier CLI
sessions — not what the user just did inside the TUI.
Intercept `/history` as a local slash command so it dumps
`ctx.local.getHistoryItems()` — the TUI's own transcript — routed
through the pager (which scrolls after #13591). Accepts an optional
preview-length argument (default 400 chars per message).
Adds createSlashHandler coverage.