Why: the completion doc assigns the Memory port to the library; today
memory recall is a product-side interface assertion with no library
surface, AgentSpec.MemoryScope has no consumer, and the model has no
write-back path.
Evidence: GOWORK=off go vet + go test -count=1 ./... green;
TestLoopInjectsMemoryAndRegistersWrite (recall block lands after the
system section, memory_write executes through the loop),
TestEmptyRecallInjectsNothing (empty recall changes nothing),
TestBlockRenderOrderingAndCaps (deterministic order, expiry/empty
pruning), TestWriteToolValidation (fail-closed scope/type/content).
Impact: new opt-in Config.Memory/MemoryScope; nil port keeps behavior
byte-identical; injection is request-scoped (never persisted, never
accumulates) and deterministic ([记忆] text shape preserved for the
product migration).
Refs: Agent-System-Documents#43 (N3 plan WP5)
