Add assurance structs (#26)

internal/block/assurance.go

@@ -0,0 +1,20 @@
+package block
+
+import "github.com/eigerco/strawberry/internal/crypto"
+
+// Assurance represents a single validator's attestation of data availability
+// for work reports on specific cores. It is part of the Assurances Extrinsic (E_A).
+// Each Assurance contains:
+// - An anchor to the parent block
+// - A bitstring flag indicating availability for each core
+// - The index of the attesting validator (0 to 1023)
+// - A signature validating the assurance
+// Assurances must be ordered by validator index in the extrinsic.
+type Assurance struct {
+	Anchor         crypto.Hash                       // Parent block hash (a ∈ H)
+	Flag           bool                              // Bitstring of assurances, one bit per core (f ∈ B_C)
+	ValidatorIndex uint16                            // Index of the attesting validator (v ∈ N_V)
+	Signature      [crypto.Ed25519SignatureSize]byte // Ed25519 signature (s ∈ E)
+}
+
+type AssurancesExtrinsic []Assurance

internal/block/block.go

@@ -11,4 +11,5 @@ type Extrinsic struct {
 	ET []*TicketProof
 	EP *PreimageExtrinsic
 	ED *DisputeExtrinsic
+	EA *AssurancesExtrinsic
 }