task: publish the zcashd replacement contract and surface ownership table #11021

Context

"Zebra replaces zcashd" has no published boundary: nothing states, for each zcashd RPC method, notification transport, and integration surface, whether it is owned by Zebra, a named external component (Zaino, Zallet, librustzcash), a supported bridge, or an explicit non-goal. This issue publishes and maintains that ownership contract.

User Story

As an operator migrating from zcashd,
when I look up any zcashd RPC method, notification, or integration surface,
then I find a published record of whether Zebra, a named external component, a supported bridge, or nobody owns it.

Acceptance Criteria

• A published ownership table (in book/src/user/ or docs/) assigns every one of the 135 registered zcashd 6.20.0 RPC methods, all four public ZMQ topics, the data REST API, and each notification hook (blocknotify, alertnotify, txexpirynotify, walletnotify) to exactly one of: Zebra, named external component, supported bridge, or explicit non-goal.
• A deprecation-readiness definition of done — covering consensus support, surface ownership, RPC conformance, migration procedure, mining integration, wallet/indexer versioning, and no-silent-holes — is adopted in a docs/decisions/ ADR, with team sign-off recorded.
• Every "non-goal" row links the issue where that decision was made (e.g. Zebra should auto-discover its own external IP address #1893, Tracking: Create a Debian Package #7424, feature: match zcashd RPC error codes #8782, Reduce Zebra disk usage for mining pools #5718, Implement createrawtransaction RPC method #8952, feature: Implement decoderawtransaction RPC method #8645, Implement verifymessage RPC method #8947, Implement z_validatepaymentdisclosure RPC method #8443) so the decision trail is auditable.
• Every row assigned to zcashd, a bridge, or a wallet/indexer component records that owner's acknowledgment, or is downgraded to "proposed" until they respond (see External Coordination).
• Rows with no existing decision are flagged and turned into follow-up issues (task: record a disposition for each of the 33 zcashd node and utility RPC methods missing from Zebra #11022, task: decide and document connect-only topology and relay-policy controls #11027, and task: resolve or record the remaining untracked shared-RPC differences #11033 cover the known ones).
• A maintenance rule is documented: the table must be updated in the same PR that adds, removes, or intentionally diverges from a zcashd-compatible public surface, and refreshed for every Zebra stable release.
• A CHANGELOG.md entry announces the published contract (user-visible documentation change).

Implementation Details

The contract has three parts: a node/operator capability matrix, the RPC ownership table (zcashd 6.20.0 registers 135 method names in a default wallet-enabled build; Zebra registers 37, with 35 shared), and the definition of done; the zcash.conf → zebrad.toml translation table is #11038's deliverable and is linked, not duplicated. The work is editorial and decision-driven, not code: publish as a book page (e.g. book/src/user/zcashd-ownership.md, wired into book/src/SUMMARY.md) and hold the product decisions for unassigned rows. Method inventories should be extracted from the Rpc trait in zebra-rpc/src/methods.rs (registration starts around line 177) and the zcashd 6.20.0 command tables; the existing comparison spreadsheet is the starting point for the table content. The ADR belongs in docs/decisions/ following the existing MADR format there.

In Scope

• book/src/user/ (new ownership page), book/src/SUMMARY.md
• docs/decisions/ (new ADR for the deprecation-readiness definition)
• CHANGELOG.md

Out of Scope

• Per-method dispositions for the 33 missing node/utility methods (task: record a disposition for each of the 33 zcashd node and utility RPC methods missing from Zebra #11022).
• Connect-only and relay-policy product decisions (task: decide and document connect-only topology and relay-policy controls #11027).
• Fixture/conformance implementation (task: define the RPC conformance fixture format and capture zcashd reference responses #11023, task: add conformance fixtures for the 12 near-compatible shared RPC methods #11024, task: add conformance fixtures for the divergent chain and block query RPC methods #11025, task: add conformance fixtures for the divergent mining, mempool, and node RPC methods #11026).
• The operator migration runbook content (task: publish a zcashd-to-Zebra migration guide and recovery runbook in the book #11038).
• Any code changes to zebra-rpc or zebra-network.

External Coordination

Rows assigned to zcashd, Zaino, Zallet, or librustzcash need acknowledgment from those projects' owners to count as a contract rather than a proposal — including a zcashd build supported past the height-3,417,100 End-of-Support halt wherever a bridge depends on one. Work on their side belongs in their trackers.

Blockers

None.

Related Issues / Advisories

• Wallet/legacy-RPC path: PoC: JSON-RPC wrapper around Zebra and Zaino #9392, feature: Consolidated RPC documentation for new Zcash network architecture #9160, feat(zebrad): add zcashd-compat mode with a supervised zcashd wallet sidecar #10952

Expertise Required

None.