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Move the "Changes to ZIP 221" section from ZIP 229 into ZIP 258
The NU6.3 deployment ZIP (258) already absorbed the "Changes to ZIP 209" and the corresponding § 4.17 protocol-spec changes in zcash#1301; move the "Changes to ZIP 221" (Ironwood history-tree metadata) there too, so that all of the cross-ZIP consensus/spec edits live in the deployment ZIP rather than the transaction-format ZIP. Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Signed-off-by: Daira-Emma Hopwood <daira@jacaranda.org>
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‎zips/zip-0229.md‎

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@@ -412,71 +412,6 @@ digest — which now includes the Ironwood auth digest, and (per the change abov
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no further structural change.
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## Changes to ZIP 221
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The history tree that commits to chain history [^zip-0221] gains Ironwood metadata, exactly
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as it gained Orchard metadata at NU5. The new fields are computed and aggregated identically
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to the corresponding `...Orchard...` fields.
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In the "Tree Node specification" section, after field 14 `nOrchardTxCount`, add:
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> 15. [NU6.3 onward] `hashEarliestIronwoodRoot`
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>
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> Leaf node
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> Calculated as the note commitment root of the final Ironwood treestate
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> (similar to `hashEarliestOrchardRoot`).
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>
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> Internal or root node
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> Inherited from the left child.
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>
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> Serialized as `char[32]`.
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>
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> 16. [NU6.3 onward] `hashLatestIronwoodRoot`
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>
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> Leaf node
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> Calculated as the note commitment root of the final Ironwood treestate
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> (similar to `hashLatestOrchardRoot`).
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>
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> Internal or root node
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> Inherited from the right child.
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>
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> Serialized as `char[32]`.
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>
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> 17. [NU6.3 onward] `nIronwoodTxCount`
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>
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> Leaf node
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> The number of transactions in the leaf block where `vActionsIronwood`
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> is non-empty.
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>
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> Internal or root node
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> The sum of the `nIronwoodTxCount` field of both children.
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>
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> Serialized as `CompactSize uint`.
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Replace
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> The fields marked "[NU5 onward]" are omitted before NU5 activation [^zip-0252].
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>
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> Each node, when serialized, is between 147 and 171 bytes long (between 212 and 244 bytes
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> after NU5 activation). [...]
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with
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> The fields marked "[NU5 onward]" are omitted before NU5 activation [^zip-0252]. The fields
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> marked "[NU6.3 onward]" are omitted before NU6.3 activation.
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>
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> Each node, when serialized, is between 147 and 171 bytes long (between 212 and 244 bytes
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> after NU5 activation, and between 277 and 317 bytes after NU6.3 activation). [...]
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The pseudocode node structure and `serialize` / `make_leaf` / `make_parent` functions are
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extended with `hashEarliestIronwoodRoot`, `hashLatestIronwoodRoot`, and `nIronwoodTxCount`
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in the same way the "# NU5 only" Orchard fields were added (present iff NU6.3 has activated;
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the roots inherited from the left/right child and the count summed, in internal nodes).
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`hashChainHistoryRoot` continues to be the BLAKE2b-256 digest of the serialized root node;
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its value changes at NU6.3 only through the added node fields. The `hashBlockCommitments`
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header field [^zip-0244] is unaffected beyond this.
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# Rationale
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The main purpose of the NU6.3 network upgrade is to bolster confidence in Zcash's supply
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[^zip-0209]: [ZIP 209: Prohibit Negative Shielded Chain Value Pool Balances](zip-0209.rst)
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[^zip-0221]: [ZIP 221: FlyClient - Consensus-Layer Changes](zip-0221.rst)
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[^zip-0224]: [ZIP 224: Orchard Shielded Protocol](zip-0224.rst)
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[^zip-0225]: [ZIP 225: Version 5 Transaction Format](zip-0225.rst)

‎zips/zip-0258.md‎

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pool balance alongside those for the existing *Sprout*, *Sapling*, and *Orchard pools*. These
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mirror the changes above and are not spelled out here.
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## Changes to ZIP 221
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The history tree that commits to chain history [^zip-0221] gains Ironwood metadata, exactly
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as it gained Orchard metadata at NU5. The new fields are computed and aggregated identically
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to the corresponding `...Orchard...` fields.
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In the "Tree Node specification" section, after field 14 `nOrchardTxCount`, add:
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> 15. [NU6.3 onward] `hashEarliestIronwoodRoot`
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>
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> Leaf node
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> Calculated as the note commitment root of the final Ironwood treestate
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> (similar to `hashEarliestOrchardRoot`).
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>
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> Internal or root node
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> Inherited from the left child.
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>
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> Serialized as `char[32]`.
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>
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> 16. [NU6.3 onward] `hashLatestIronwoodRoot`
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>
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> Leaf node
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> Calculated as the note commitment root of the final Ironwood treestate
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> (similar to `hashLatestOrchardRoot`).
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>
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> Internal or root node
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> Inherited from the right child.
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>
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> Serialized as `char[32]`.
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>
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> 17. [NU6.3 onward] `nIronwoodTxCount`
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>
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> Leaf node
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> The number of transactions in the leaf block where `vActionsIronwood`
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> is non-empty.
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>
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> Internal or root node
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> The sum of the `nIronwoodTxCount` field of both children.
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>
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> Serialized as `CompactSize uint`.
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Replace
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> The fields marked "[NU5 onward]" are omitted before NU5 activation [^zip-0252].
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>
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> Each node, when serialized, is between 147 and 171 bytes long (between 212 and 244 bytes
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> after NU5 activation). [...]
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with
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> The fields marked "[NU5 onward]" are omitted before NU5 activation [^zip-0252]. The fields
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> marked "[NU6.3 onward]" are omitted before NU6.3 activation.
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>
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> Each node, when serialized, is between 147 and 171 bytes long (between 212 and 244 bytes
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> after NU5 activation, and between 277 and 317 bytes after NU6.3 activation). [...]
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The pseudocode node structure and `serialize` / `make_leaf` / `make_parent` functions are
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extended with `hashEarliestIronwoodRoot`, `hashLatestIronwoodRoot`, and `nIronwoodTxCount`
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in the same way the "# NU5 only" Orchard fields were added (present iff NU6.3 has activated;
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the roots inherited from the left/right child and the count summed, in internal nodes).
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`hashChainHistoryRoot` continues to be the BLAKE2b-256 digest of the serialized root node;
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its value changes at NU6.3 only through the added node fields. The `hashBlockCommitments`
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header field [^zip-0244] is unaffected beyond this.
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## ZIP 2005 activation
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ZIP 2005 [^zip-2005] activates at NU6.3: its $\mathsf{ZIP2005ActivationHeight}$ (also referenced
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[^zip-0209]: [ZIP 209: Prohibit Negative Shielded Chain Value Pool Balances](zip-0209.rst)
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[^zip-0221]: [ZIP 221: FlyClient - Consensus-Layer Changes](zip-0221.rst)
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[^zip-0229]: [ZIP 229: Version 6 Transaction Format](zip-0229.md)
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[^zip-0244]: [ZIP 244: Transaction Identifier Non-Malleability](zip-0244.rst)
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[^zip-0252]: [ZIP 252: Deployment of the NU5 Network Upgrade](zip-0252.rst)
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[^zip-0256]: [ZIP 256: Deployment of Consensus Bug Fixes Between NU6.1 and NU6.2](zip-0256.md)
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[^zip-0318]: [ZIP 318: Orchard to Ironwood Migration](zip-0318)

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