Control UI chat startup coalesces model and command metadata

Control UI chat startup gets faster: a new negotiated `chat.metadata` Gateway RPC coalesces the configured model catalog and text slash commands, and metadata builders are now dynamically imported only inside `chat.metadata`, keeping the first chat message path free of the metadata dependency graph [1]. Old-gateway fallback to `models.list` plus `commands.list` is preserved, with stale selected-agent guards and agent-scoped model visibility [1].

A shared channel progress draft compositor now consolidates progress for tool, commentary, and reasoning across channels: Discord was moved to it, and Telegram progress drafts route through the same path [2]. Regressions cover hidden progress details, suppressed drafts, tagged reasoning, and repeated reasoning snapshots [2]. Meanwhile, internal agent and tool trace-line stripping moved into the shared assistant-visible text sanitizer, so non-Discord delivery users get the same suppression for failed-tool payloads that Discord already had [3]. Discord keeps its stricter send-boundary guard for plain internal labels like `analysis:`, `commentary:`, `thinking:`, and `reasoning:`; trace-only error-context payloads get stripped before user-facing delivery, while explicit tool-progress and non-text Discord payloads are preserved [3].

Telegram `/new` and hard `/reset` session-boundary detection no longer materializes every previous cached message, thanks to a targeted message-cache helper that looks for the latest matching message at or before the current one [4]. Previously the code scanned with `recentBefore(..., Number.MAX_SAFE_INTEGER)`; now current-message and previous-message boundary selection folds into one cache scan, leaving `recentBefore` and `around` behavior unchanged [4].