Initial version of CIP for introducing a default SPO vote

Author: teodanciu

CIP-XXXX/README.md

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+---
+CIP: XXXX
+Title: Default SPO vote
+Category: Ledger
+Authors:
+  - Teodora Danciu <[email protected]>
+  - Alexey Kuleshevich <[email protected]>
+Implementors: N/A
+Status: Proposed
+Discussions:
+  - https://github.com/cardano-foundation/CIPs/pull/1108
+  - https://github.com/IntersectMBO/cardano-ledger/issues/4645
+Created: 2025-10-28
+License: CC-BY-4.0
+---
+
+## Abstract
+
+We propose introducing an explicit mechanism for SPOs to define their default governance vote as part of their pool's registration parameters.
+This would replace the current indirect approach, which relies on delegating the pool’s reward account to predefined DReps AlwaysNoConfidence and AlwaysAbstain.
+
+## Motivation: why is this CIP necessary?
+
+The current approach was always intended as a temporary workaround. While it solved the immediate problem (as discussed in [cardano-ledger#4645](https://github.com/IntersectMBO/cardano-ledger/issues/4645)), it introduces several issues:
+  * It is not transparent or easily inspectable what a pool’s default vote actually is, making it difficult to understand how undelegated or non-voting stake will behave in governance actions.
+  * It couples operational reward accounts with governance semantics, constraining how SPOs can use their reward accounts.
+  * It can distort governance outcomes, as SPOs who do not configure their reward accounts may unintentionally default to voting No, potentially skewing proposal results.
+
+By contrast, providing SPOs with a clear, explicit default vote parameter allows them to opt in or out of governance participation transparently, mitigating the coupling between financial and governance mechanisms and reducing long-term bias in voting behaviour.
+
+## Specification
+
+### Current behaviour
+
+The "default vote" determines how *not voting* counts toward the ratification of a proposal.
+For SPOs, this is currently implemented as folllows:
+  * `HardForkInitiation` proposals: default is `No`
+  * `NoConfidence` proposals:
+      - if the pool's reward account is delegated to `AlwaysNoConfidence`, the default is `Yes`
+      - otherwise, `No`
+  * `UpdateCommittee` and `ParameterUpdate` (for security-group parameters) proposals:
+      - if the pool reward account is delegated to `AlwaysAbstain`, the default is `Abstain`
+      - otherwise, `No`
+
+### Proposed changes
+
+Add a new non-optional field to the pool parameters that specifies the SPO's default vote, with 3 possible values:
+  * `DefaultNoConfidence`: `Yes` on `NoConfidence`, `No` on all other actions (matches delegation to `AlwaysNoConfidence`)
+  * `DefaultAbstain`: `Abstain` on all actions (matches delegation to `AlwaysAbstain`)
+  * `NoDefault`: `No` on all actions (matches no delegation to a default DRep)
+
+<br>
+
+Currently the pool parameters are specified in cddl like this:
+
+```cddl
+pool_params =
+  ( operator       : pool_keyhash
+    , vrf_keyhash    : vrf_keyhash
+    , pledge         : coin
+    , cost           : coin
+    , margin         : unit_interval
+    , reward_account : reward_account
+    , pool_owners    : set<addr_keyhash>
+    , relays         : [* relay]
+    , pool_metadata  : pool_metadata/ nil
+  )
+```
+
+The proposed definition is:
+```cddl
+pool_params =
+  ( operator       : pool_keyhash
+    , vrf_keyhash    : vrf_keyhash
+    , pledge         : coin
+    , cost           : coin
+    , margin         : unit_interval
+    , reward_account : reward_account
+    , pool_owners    : set<addr_keyhash>
+    , relays         : [* relay]
+    , pool_metadata  : pool_metadata/ nil
+    , default_vote   : stakepool_default_vote
+  )
+
+stakepool_default_vote = default_vote_abstain / default_vote_no_confidence / no_default_vote
+default_vote_abstain = 0
+default_vote_no_confidence = 1
+no_default_vote  = 2
+```
+
+This change requires a hard fork, since it modifies transaction serialization.
+
+### Migration of currently configured default votes
+
+At the hard-fork boundary, the pool parameters of each existing pool will be updated to reflect the implicit preference currently expressed through its reward account delegation.
+For each pool, we'll set the new `defaultVote` parameter to:
+  * `DefaultAbstain`, if the reward account is delegated to `AlwaysAbstain`
+  * `DefaultNoConfidence`, if the reward account is delegated to `AlwaysNoConfidence`
+  * `NoDefault`, if the reward account is not delegated to a defaul DRep
+
+## Path to Active
+
+### Acceptance Criteria
+
+- [ ] Transaction serializers and deserializers in [cardano-ledger](https://github.com/IntersectMBO/cardano-ledger) are implemented such that they follow the cddl specification described above, and reflected in the cddl specs
+- [ ] The migration of the existing default vote preferences is implemented in ledger
+- [ ] The feature is integrated into [cardano-node](https://github.com/IntersectMBO/cardano-node) with necessary adjustments made to [ouroboros-consensus](https://github.com/IntersectMBO/ouroboros-consensus) and released as part of the Dijkstra era hard fork
+
+### Implementation Plan
+
+- [ ] Add support for a new pool parameter without changing serialization in existing eras
+- [ ] Implement and test migration logic to populate the new parameter at the hard-fork boundary.
+
+## Copyright
+
+This CIP is licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/legalcode).