P2-1 (agent-runner.ts): Restrict direct completion notice to
block-streaming runs. The condition now checks blockStreamingEnabled
in addition to opts?.onBlockReply, preventing duplicate completion
notices in non-streaming sessions where verboseNotices already handles
the compaction-complete text.
P2-2 (agent-runner-execution.ts): Emit compaction start notice when
streaming is off. blockReplyHandler is a no-op for non-streaming runs,
so add a direct fallback path: when blockStreamingEnabled is false and
opts.onBlockReply is present, send the start notice directly with
applyReplyToMode threading applied.
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