Background-session classifier gains a chat-relay mode and ignores virtual messages

What

Claude Code can run sessions in the background, and a classifier gives each one its status text. A classifier here is a step that reads the session's messages and decides what state it is in, such as blocked or failed. This release changes what that classifier reads and how it behaves.

• Virtual messages (marked isVirtual) are now filtered out before classification. Before, every message counted.
• A new chatRelay mode is passed into the classify call. One finding saw it set from a size check. The other saw it set only when n.chatRelay === true, the recap flag is off, the engine is the llm one, and one more check passes.
• In chatRelay mode, the quick pre-classification result is skipped unless its state is blocked or failed.
• A new CLASSIFIER_CHAT_RELAY_ADDENDUM block is added to the classifier's instructions in this mode.
• Script posts are also passed into the classify call.
• Whether chatRelay was on is now recorded with each classification.

Why

This changes how the status text for background sessions is worked out, adding a separate path for sessions whose chat is relayed. Status lines for those sessions may read differently. Virtual messages no longer affect the status of any session.