Adds a router middleware that extracts the X-Session-Tag header from
each request and decorates the request context via
project_events.WithSessionTag. Service- and model-layer publishers
then read it back via project_events.SessionTagFromContext and
attach it to outgoing CardMoved / CardLinked / CardUnlinked events.
The originating browser tab compares the incoming session_tag to
its own and skips the echo, avoiding double-application of the
optimistic local update. Other tabs see no tag match and apply the
event normally.
Wired into both the web router chain (before Contexter so the base
context inherits the tag) and the API router chain (before
APIContexter for the same reason).
Oleks
47f3e4137e