Require analyzed source manifests before project actions

Why: A durable observation receipt must not be mistaken for completed risk analysis or permission to execute a project action.

Evidence: Exact-source preflight tests cover pending versus proceed, partial attachment, post-ACK source tampering, current authorization, and receipt idempotency; go test -p 1 ./... and go build ./... passed.

Impact: Add a fail-closed host preflight helper and per-message manifest read, still unwired to the public product path pending recovery and four-route coverage.

Refs: TT-N03, TT-R01; approved X3 design r1

pkg/extension/project_work.go

@@ -29,6 +29,7 @@ type WorkObservation struct {
 	Text               string    `json:"text,omitempty"` // only the actual authorized fragment
 	Scope              string    `json:"scope"`          // private|project|controlled
 	Delivery           string    `json:"delivery"`       // complete|summary-only|partial
+	DeliveryReason     string    `json:"deliveryReason,omitempty"`
 	AuthorizationEpoch string    `json:"authorizationEpoch"`
 	ObservedAt         time.Time `json:"observedAt"`
 }