feat(wasm-utxo): add orchard (no-circuit) dep + Ironwood PCZT serialization

Introduce the `orchard` crate WITHOUT the `circuit` feature (Sinsemilla /
pasta / note-encryption only — no halo2 prover) plus `rand`, `postcard`,
and `ff`, and add the `zcash::ironwood_pczt` module that (de)serializes an
`orchard::pczt::Bundle`.

`orchard::pczt::Bundle` is not serde-serializable, so this bridges it to a
compact wire form: a 1-byte format version + a `postcard`-encoded mirror
struct whose fields are exactly what orchard's `Bundle/Action/Spend/
Output::parse(...)` consume. Serialize reads the bundle's public getters;
deserialize reconstructs via `parse(...)`. This is the witness payload
exchanged with the external Ironwood proof service and carried through the
PSBT (proving is delegated; no halo2 in wasm-utxo).

Notes:
- `>32`-byte fields are stored as `Vec<u8>` (serde derives arrays only up
  to length 32) and length-checked on the way back in.
- `note_version` is derived from the bundle version rather than carried on
  the wire; `zip32_derivation` (wallet metadata the prover doesn't need) is
  dropped.
- `serde` is now a non-optional dependency (the module derives
  Serialize/Deserialize); the `inspect` feature drops its `dep:serde`.

Verified: compiles for wasm32-unknown-unknown and native; a build ->
serialize -> deserialize -> re-serialize round-trip is byte-stable.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: 2 people

packages/wasm-utxo/Cargo.lock

@@ -22,7 +22,7 @@ unexpected_cfgs = { level = "warn", check-cfg = [
 
 [features]
 default = []
-inspect = ["dep:num-bigint", "dep:serde", "dep:serde_json", "dep:hex"]
+inspect = ["dep:num-bigint", "dep:serde_json", "dep:hex"]
 
 [dependencies]
 wasm-bindgen = "0.2"
@@ -37,10 +37,24 @@ musig2 = { version = "0.3.1", default-features = false, features = ["k256"] }
 getrandom = { version = "0.2", features = ["js"] }
 pastey = "0.1"
 num-bigint = { version = "0.4", optional = true }
-serde = { version = "1.0", features = ["derive"], optional = true }
+# serde is non-optional: the Ironwood PCZT serialization (always compiled) derives Serialize/
+# Deserialize for its postcard mirror struct.
+serde = { version = "1.0", features = ["derive"] }
 serde_json = { version = "1.0", optional = true }
 hex = { version = "0.4", optional = true }
 
+# Orchard/Ironwood shielded-bundle construction (PCZT Constructor/Signer/Extractor).
+# `default-features = false` DROPS the `circuit` feature, so halo2_proofs/halo2_gadgets
+# (the heavy prover) are NOT pulled in — only Sinsemilla/pasta/note-encryption. Proving is
+# delegated to an external service.
+orchard = { version = "0.15", default-features = false, features = ["std"] }
+rand = "0.8"
+# Compact deterministic encoding of the Ironwood PCZT witness (proof-service payload / PSBT carry).
+postcard = { version = "1.0", features = ["use-std"] }
+# `ff::PrimeField::to_repr` for the one PCZT witness field (`alpha`, a Pallas scalar) that orchard
+# exposes only as a curve scalar. Already in-tree via orchard/pasta_curves.
+ff = "0.13"
+
 # Pinned to avoid RUSTSEC-2026-0204 (invalid pointer dereference in fmt::Pointer)
 crossbeam-epoch = ">=0.9.20"