Summary

Raise the chat.history text cap from 12_000 to 64_000 and make truncation UTF-8 byte-aware so long assistant replies stay readable instead of being replaced by the oversized placeholder.

What changed

• bumped CHAT_HISTORY_TEXT_MAX_CHARS in src/gateway/server-methods/chat.ts from 12_000 to 64_000
• added a byte-aware fallback inside truncateChatHistoryText() so UTF-8-heavy text is truncated to a safe prefix before the 128 * 1024 single-message byte guard runs
• added a regression test for a 50k-character ASCII assistant reply that should be preserved intact
• added a regression test for an emoji-heavy assistant reply that should truncate visibly instead of collapsing to [chat.history omitted: message too large]

Why

Before this change, chat.history truncated content[].text, partialJson, arguments, and thinking at 12k characters before the larger byte-budget logic ran.

Raising the char cap alone fixes premature truncation for long ASCII replies, but it leaves a second failure mode: long UTF-8-heavy text can bypass the char cap and then be replaced entirely by the oversized placeholder during the later byte-budget pass.

This update fixes both paths:

• long replies that still fit the budget remain visible
• byte-heavy replies are truncated to a readable prefix instead of being dropped completely

Test

pnpm -C /tmp/openclaw-pr-53243 exec vitest run --config vitest.gateway.config.ts src/gateway/server.chat.gateway-server-chat-b.test.ts

Fixes openclaw#53242