Conversation Continuity
What Changed Since Last Scan?
Unread tells you what you have not opened. Change tells you what became newly consequential.
Most inbox views are snapshots.
Unread shows what you have not opened. Recent shows what arrived last. Search shows what you can retrieve when you already know what to ask for.
None of those naturally answer a more useful question: what changed while I was not looking?
Delta can matter more than state
A prospect who was quiet for eight days replies. A client thread shifts from waiting on them to waiting on you. A stakeholder joins a conversation. A promise crosses its expected window. A thread that looked resolved becomes active again.
The important information is not just the current thread. It is the difference between the thread now and the thread before.
A radar becomes useful when it remembers enough of the previous state to notice the delta.
Why recency is a weak proxy
Recency treats every new message as a reason to rise.
But a new calendar notification and a revived investor conversation can arrive one second apart and deserve completely different levels of attention. The timestamp is real. The consequence is not encoded in it.
Change detection adds context: this person was silent, now they replied; this thread was theirs, now it is yours; this conversation was warm, now the timing window is narrowing.
The product implication
This is why Sidekick Log needs memory even though Gmail already stores the messages.
Gmail is the source of truth for the conversation. Sidekick Log only needs enough derived state to ask whether something meaningful changed.
The longer-term version of that idea is broader than email: useful software should notice changes in your world that alter what deserves attention, even when you did not know to search for them.