fix(light-client): bound leaf proof construction to prevent OOM

crates/espresso/node/api/light-client.toml

@@ -16,7 +16,7 @@ PATH = [
 ":payload-hash" = "TaggedBase64"
 DOC = """
 Fetch a leaf plus a proof of it's finality (a chain of leaves leading from that leaf to either a
-chain of consecutive valid QCs or a known-finalized leaf).
+chain of consecutive valid QCs, a finality certificate, or a known-finalized leaf).
 
 `:height` and `:finalized`, if provided, must both be block numbers. If provided, `:finalized` must
 be greater than `:height`.
@@ -27,8 +27,14 @@ to be finalized). This consists of a chain of valid leaves from the requested le
 either
 * a 2-chain of QCs (if the last leaf in the leaf chain is from HotShot >= 0.3)
 * a 3-chain of QCs (if the last leaf in the leaf chain is from HotShot < 0.3)
+* a certificate directly committing the last leaf in the chain (HotShot >= 0.6)
 * the assumed `:finalized` leaf
 
+The server bounds the number of leaves it will include in a single proof. The `:finalized` hint is
+ignored if it is too far past the requested leaf for a bounded proof, or if a finality certificate
+nearer the requested leaf yields a shorter proof; the proof instead ends in a QC chain or
+certificate, which the client must verify against the appropriate quorum.
+
 Returns
 ```json
 {
@@ -47,6 +53,12 @@ Returns
             "deciding_qc": QC
         } | undefined,
 
+        // Finality proof for HotShot >= 0.6
+        "NewProtocol": {
+            "cert2": Certificate2,
+            "leaf_qc": QC
+        } | undefined,
+
         // Leaf chain ends in assumed-finalized leaf.
         "Assumption": {}
     }