fix: duplicate user message on first send in a new tab

When a draft is promoted to a real conversation, send() appends the
user message as a provisional chunk (optimistic echo). But load()
also fires syncTail, which fetches the CR-6 persisted user message
as a committed chunk — showing the message twice until turn seal.

Fix: applyHistory now removes provisional chunks that duplicate the
last committed chunk (matching role + text content) when new committed
chunks arrive during generation. The optimistic echo is dropped once
the authoritative committed version arrives.

684 tests green.

0 files changed, 0 insertions, 0 deletions