The conversation fixture used an undeclared goal source and forced it
through MessageSource with a double assertion. That bypassed the V4
producer-owned source types instead of exercising an input accepted by
createUserMessage.
Use the fixture's existing declared test source for both injected plugin
messages and remove the unused MessageSource import. The resolver excludes
all non-user, non-checkpoint sources, so these cases do not depend on goal
identity or need a goal-package dependency. Message content, event order,
captured sequence numbers, and every projection assertion stay unchanged.
Validation: all 49 session-reference tests pass, the Host TypeScript
aggregate passes, and the diff passes whitespace checks.
Tianyi Cui
370e1efcdb