- ConversationWindowManager: cap reserve token at 50% of effective max
to prevent negative historyBudget on small-context models (8K/16K)
- common.security.SecretEquals: new constant-time comparison utility
(MessageDigest.isEqual wrapper) for secrets/tokens/signatures
- WeixinChannelAdapter: migrate context_token comparison to SecretEquals
- FeishuChannelAdapter: fail-fast on empty encrypt_key when connection_mode=webhook
- TelegramChannelAdapter: sanitize attachment captions — strip control bytes
(\p{Cc} except \t\r\n) + format chars (\p{Cf}) + 4096 char cap
- AgentGraphBuilder: fallback Anthropic max_tokens to 4096 on null/0/negative
Tests: SecretEqualsTest (5) + TelegramCaptionSanitizeTest (5) — all green.
