When enforceFinalTag is active (Google providers), stripBlockTags
correctly returns empty for text without <final> tags. However, the
handleMessageEnd fallback recovered raw text, bypassing this protection
and leaking internal reasoning (e.g. "**Applying single-bot mention
rule**NO_REPLY") to Discord.
Guard the fallback with enforceFinalTag check: if the provider is
supposed to use <final> tags and none were seen, the text is treated
as leaked reasoning and suppressed.
Also harden stripSilentToken regex to allow bold markdown (**) as
separator before NO_REPLY, matching the pattern Gemini Flash Lite
produces.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>