zod 3.25 (the version resolved by ^3.25.0) requires z.record() to take
both a key and a value schema. The single-arg form z.record(z.unknown())
is zod v4 syntax, which trips next build's typecheck.
Four call sites in packages/shared/src/schemas/agent.ts were written in
v4 form (lines 39, 41, 73, 74). This is a pure type-only fix — runtime
behavior is identical.