Migrate Ironwood to the official librustzcash RC (+ merge upstream)

[emersonian]

Draft. Moves the Ironwood work off the Valar Group librustzcash fork and onto the official librustzcash Ironwood release candidate, and folds in the latest upstream zcash/zcash-devtool.

Supersedes c85bcb4 ("Supply NU6.3 activation heights for testnet/mainnet")

That commit hand-added a testnet NU6.3 override (4_134_000) because the fork's zcash_protocol returned None for NU6.3 on the production networks. The official RC ships that testnet height natively, so the override — and the whole src/network.rs wrapper it lived in — is removed. The tool now uses upstream's data::Network, which implements Parameters directly. (Confirmed: derivation/sync treat Ironwood as active on testnet with no override.)

Dependencies

• [patch.crates-io] → zcash/librustzcash rev 4b13be3c (the commit the zcash_*-*-pre.* RC tags point to), replacing valargroup/librustzcash.
• Bumped to RC versions: zcash_primitives/zcash_proofs 0.29.0-pre.0, zcash_keys 0.15.0-pre.0, zcash_protocol 0.10.0-pre.0, zcash_transparent 0.9.0-pre.0, zcash_address 0.13.0-pre.0.
• orchard pinned to =0.15.0-pre.1 from crates.io (the RC uses it directly); the orchard git patch is dropped. halo2 unchanged.

No more cfg gate

Ironwood is the stable Nu6_3 upgrade in the RC (→ V6 transactions), so it builds on a plain cargo build:

• Removed .cargo/config.toml (no more --cfg zcash_unstable="nu6.3").
• Added the now-ungated nu6_3 key to the regtest ActivationHeights schema and the inspect UFVK construction.

RC API adaptations

• Pczt::serialize() now returns Result — handled at every call site.
• propose_send_max_transfer dropped proposed_version; SendMaxErrorT uses BalanceError (ProposeSendMaxErrT).
• pay-manual's Orchard BundleView is a (BundleVersion, inputs, outputs) tuple.

Removed wallet migrate-to-ironwood

It wrapped create_orchard_to_ironwood_transaction, which exists only in the Valar fork; the official RC has no equivalent (its wallet still builds V6 transactions with ironwood_anchor: None). Everything else Ironwood-related stays: V6 build/inspect, PCZT Ironwood proofs, and V6 emission via the standard send path once a chain is ≥ NU6.3. Easy to reinstate when an upstream helper lands.

Upstream merge

Includes upstream zcash/zcash-devtool main: configurable regtest --activation-heights (persisted per wallet), non-interactive init, wallet get-info, restore-mnemonic, ZecRocks testnet servers, and more.

Network activation

Network	NU6.3 (Ironwood)	Status
mainnet	not yet scheduled (None)	works automatically once upstream assigns a height
testnet	4_134_000 (from zcash_protocol)	works today
regtest	operator-chosen via --activation-heights (nu6_3 key)	active from any height you set

Docs

doc/ironwood.md rewritten for the RC: activation model, step-by-step regtest usage, the cross-component height invariant, and the official Zebra v6.0.0-rc.0 companion (confirm exact node/indexer tags against the current RC before a run).

Verification

• cargo build (default and --features regtest_support)
• cargo test --features regtest_support (3/3, incl. regtest activation-height round-trip)
• cargo clippy --all-targets --features regtest_support -- -D warnings (clean)
• Runtime: address derivation exercised on regtest/testnet/mainnet.

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