What Problem This Solves

Twitch outbound text had two raw UTF-16 splitters. OpenClaw's markdown-aware planner could bisect an emoji at its 500-unit hard boundary, and the Twurple 8.1.4 ChatClient.say() fallback uses the same unsafe raw slicing when a caller sends more than 500 units.

Why This Change Was Made

Reuse the public surrogate-safe outbound chunker in both places that own the invariant:

• the Twitch markdown planner strips formatting, then delegates its word/hard boundaries to the shared helper;
• TwitchClientManager.sendMessage pre-chunks every transport send before Twurple receives it.

The monitor fallback now routes through that canonical manager path instead of calling ChatClient.say() directly. A single Twitch limit constant keeps adapter metadata and transport enforcement aligned.

User Impact

Emoji and other supplementary-plane characters remain intact when Twitch replies cross the 500-unit boundary. Chunk order is deterministic, and all normal outbound, message-adapter, direct internal, and inbound-reply fallback sends share the same transport guard.

Evidence

• Direct dependency inspection: @twurple/chat 8.1.4 ChatClient.say() delegates to splitOnSpaces(text, 500), whose hard fallback uses raw slice().
• Blacksmith Testbox tbx_01kx7a49qv2xqp9yt3dbrt1mmh: three focused Twitch suites — 44/44 passed.
• Same Testbox: path-scoped pnpm check:changed — extension production/test typechecks, lint, import-cycle, and repository guards passed.
• Fresh autoreview — clean, correctness 0.94.
• Regressions cover markdown planning, exact transport calls at the 499 ASCII units + emoji boundary, and fallback routing through the guarded sender.
• Production code is net smaller; git diff --check passed.