feat!: enable standalone consumers to reuse existing clients for ICS

.changelog/unreleased/api-breaking/2400-preccv.md

@@ -0,0 +1,12 @@
+- Enable existing (standalone) chains to use the existing client (and connection)
+  to the provider chain when becoming a consumer chain. This feature introduces 
+  the following API-breaking changes.
+  ([\#2400](https://github.com/cosmos/interchain-security/pull/2400))
+
+  - Add `connection_id` and `preCCV` to `ConsumerGenesisState`, the consumer 
+  genesis state created by the provider chain. If the `connection_id` is not empty,
+  `preCCV` is set to true and both `provider.client_state` and `provider.consensus_state`
+  are set to nil (as the consumer doesn't need to create a new provider client).
+  As a result, for older versions of consumers, the `connection_id` in 
+  `ConsumerInitializationParameters` must be empty and the resulting `ConsumerGenesisState`
+  needs to be adapted, i.e., both `connection_id` and `preCCV` need to be removed. 

.changelog/unreleased/features/2400-preccv.md

@@ -0,0 +1,13 @@
+- Enable existing (standalone) chains to use the existing client (and connection)
+  to the provider chain when becoming a consumer chain. This feature introduces 
+  the following changes.
+  ([\#2400](https://github.com/cosmos/interchain-security/pull/2400))
+
+  - Add `connection_id` to `ConsumerInitializationParameters`, the ID of 
+  the connection end _on the provider chain_ on top of which the CCV channel will 
+  be established. Consumer chain owners can set `connection_id` to a valid ID in 
+  order to reuse the underlying clients.
+  - Add `connection_id` to the consumer genesis state, the ID of the connection 
+  end _on the consumer chain_ on top of which the CCV channel will be established.
+  If `connection_id` is a valid ID, then the consumer chain will use the underlying 
+  client as the provider client and it will initiate the channel handshake.

.changelog/unreleased/state-breaking/2400-preccv.md

@@ -0,0 +1,3 @@
+- Enable existing (standalone) chains to use the existing client (and connection)
+  to the provider chain when becoming a consumer chain.
+  ([\#2400](https://github.com/cosmos/interchain-security/pull/2400))

FEATURES.md

@@ -2,22 +2,23 @@
 
 The following table indicates the major ICS features available in the [currently active releases](./RELEASES.md#version-matrix):
 
-| Feature | `v4.0.0` | `v4.4.0` |  `v4.5.0` | `v5.0.0` | `v5.2.0` |  `v6.1.0` |   `v6.3.0` | 
-|---------|---------:|---------:|---------:|---------:|----------:|---------:|---------:|
+| Feature | `v4.0.0` | `v4.4.0` |  `v4.5.0` | `v5.0.0` | `v5.2.0` |  `v6.1.0` | `v6.3.0` | `v6.4.0` | 
+|---------|---------:|---------:|---------:|---------:|----------:|---------:|---------:|---------:|
 | [Channel initialization: new chains](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#channel-initialization-new-chains) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Validator set update](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#validator-set-update) | ✅ |  ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Completion of unbonding operations](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#completion-of-unbonding-operations) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Consumer initiated slashing](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#consumer-initiated-slashing) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Reward distribution](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#reward-distribution) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Consumer chain removal](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/methods.md#consumer-chain-removal) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Key assignment](https://github.com/cosmos/interchain-security/issues/26) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Jail throttling](https://github.com/cosmos/interchain-security/issues/404) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Soft opt-out](https://github.com/cosmos/interchain-security/issues/851)  | ✅ | ❌ | ❌ | ✅ | ❌ | ❌ | ❌ |
-| [Channel initialization: existing chains](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#channel-initialization-existing-chains) (aka [Standalone to consumer changeover](https://github.com/cosmos/interchain-security/issues/756)) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Cryptographic verification of equivocation](https://github.com/cosmos/interchain-security/issues/732) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Jail throttling with retries](https://github.com/cosmos/interchain-security/issues/713) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [ICS epochs](https://cosmos.github.io/interchain-security/adrs/adr-014-epochs) | ❌ |  ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
-| [Partial Set Security](https://cosmos.github.io/interchain-security/adrs/adr-015-partial-set-security) | ❌ |  ✅ | ✅ | ❌ | ✅ | ✅ | ✅ |
-| [Inactive Provider Validators](https://cosmos.github.io/interchain-security/adrs/adr-017-allowing-inactive-validators) | ❌ | ❌ | ❌ | ❌ | ❌ | ✅ | ✅ |
-| [Permissionless](https://cosmos.github.io/interchain-security/adrs/adr-019-permissionless-ics) | ❌ | ❌ | ❌ | ❌ | ❌ | ✅ | ✅ |
-| [ICS Rewards in non-native denoms](https://github.com/cosmos/interchain-security/issues/1634) | ❌ | ❌ | ✅ | ❌ | ❌ | ❌ | ✅ |
+| [Validator set update](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#validator-set-update) | ✅ |  ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Completion of unbonding operations](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#completion-of-unbonding-operations) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ❌ | ❌ |
+| [Consumer initiated slashing](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#consumer-initiated-slashing) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Reward distribution](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#reward-distribution) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Consumer chain removal](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/methods.md#consumer-chain-removal) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Key assignment](https://github.com/cosmos/interchain-security/issues/26) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Jail throttling](https://github.com/cosmos/interchain-security/issues/404) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Soft opt-out](https://github.com/cosmos/interchain-security/issues/851)  | ✅ | ❌ | ❌ | ✅ | ❌ | ❌ | ❌ | ❌ |
+| [Channel initialization: existing chains](https://github.com/cosmos/ibc/blob/main/spec/app/ics-028-cross-chain-validation/overview_and_basic_concepts.md#channel-initialization-existing-chains) (aka [Standalone to consumer changeover](https://github.com/cosmos/interchain-security/issues/756)) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Cryptographic verification of equivocation](https://github.com/cosmos/interchain-security/issues/732) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Jail throttling with retries](https://github.com/cosmos/interchain-security/issues/713) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [ICS epochs](https://cosmos.github.io/interchain-security/adrs/adr-014-epochs) | ❌ |  ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
+| [Partial Set Security](https://cosmos.github.io/interchain-security/adrs/adr-015-partial-set-security) | ❌ |  ✅ | ✅ | ❌ | ✅ | ✅ | ✅ | ✅ |
+| [Inactive Provider Validators](https://cosmos.github.io/interchain-security/adrs/adr-017-allowing-inactive-validators) | ❌ | ❌ | ❌ | ❌ | ❌ | ✅ | ✅ | ✅ |
+| [Permissionless](https://cosmos.github.io/interchain-security/adrs/adr-019-permissionless-ics) | ❌ | ❌ | ❌ | ❌ | ❌ | ✅ | ✅ | ✅ |
+| [ICS Rewards in non-native denoms](https://github.com/cosmos/interchain-security/issues/1634) | ❌ | ❌ | ✅ | ❌ | ❌ | ❌ | ✅ | ✅ |
+| [Customizable Slashing and Jailing](https://cosmos.github.io/interchain-security/adrs/adr-020-cutomizable_slashing_and_jailing) | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ | ✅ |

Makefile

@@ -53,11 +53,17 @@ test-integration-cov:
 	go test ./tests/integration/... -timeout 30m -coverpkg=./... -coverprofile=integration-profile.out -covermode=atomic
 
 # run interchain tests
-# we can use PROVIDER_IMAGE_TAG and PROVIDER_IMAGE_NAME to run tests with a desired docker image,
-# including a locally built one that, for example, contains some of our changes that are not yet on the main branch.
-# if not provided, default value for PROVIDER_IMAGE_TAG is "latest" and for PROVIDER_IMAGE_NAME "ghcr.io/cosmos/interchain-security"
+# we can use PROVIDER_IMAGE_TAG, PROVIDER_IMAGE_NAME, SOUVEREIGN_IMAGE_TAG, and SOUVEREIGN_IMAGE_NAME to run tests with desired docker images,
+# including locally built ones that, for example, contain some of our changes that are not yet on the main branch.
+# if not provided, default value for PROVIDER_IMAGE_TAG and SOUVEREIGN_IMAGE_TAG is "latest" and for PROVIDER_IMAGE_NAME 
+# and SOUVEREIGN_IMAGE_NAME is "ghcr.io/cosmos/interchain-security"
 test-interchain:
-	cd tests/interchain && PROVIDER_IMAGE_NAME=$(PROVIDER_IMAGE_NAME) PROVIDER_IMAGE_TAG=$(PROVIDER_IMAGE_TAG) go test ./... -timeout 30m
+	cd tests/interchain && \
+	PROVIDER_IMAGE_NAME=$(PROVIDER_IMAGE_NAME) \
+	PROVIDER_IMAGE_TAG=$(PROVIDER_IMAGE_TAG) \
+	SOUVEREIGN_IMAGE_NAME=$(SOUVEREIGN_IMAGE_NAME) \
+	SOUVEREIGN_IMAGE_TAG=$(SOUVEREIGN_IMAGE_TAG) \
+	go test ./... -timeout 30m
 
 # run mbt tests
 test-mbt:

RELEASES.md

@@ -66,6 +66,7 @@ All missing minor release versions have been discontinued.
 | `v5.2.x` | May 9, 2025      |
 | `v6.1.x` | Sep 13, 2025     |
 | `v6.3.x` | Sep 13, 2025     |
+| `v6.4.x` | Sep 13, 2025     |
 
 ## Version Matrix
 
@@ -80,6 +81,7 @@ Versions of Golang, IBC, Cosmos SDK and CometBFT used by ICS in the currently ac
 | [v5.2.0](https://github.com/cosmos/interchain-security/releases/tag/v5.2.0) | 1.22   | v8.3.2 | v0.50.8    | v0.38.9  |      |
 | [v6.1.0](https://github.com/cosmos/interchain-security/releases/tag/v6.1.0) | 1.22   | v8.5.0 | v0.50.9    | v0.38.11 |      |
 | [v6.3.0](https://github.com/cosmos/interchain-security/releases/tag/v6.3.0) | 1.22   | v8.5.1 | v0.50.9    | v0.38.11 |      |
+| [v6.4.0](https://github.com/cosmos/interchain-security/releases/tag/v6.4.0) | 1.22   | v8.5.2 | v0.50.11   | v0.38.15 |      |
 
 **Note:** For a list of major ICS features available in the currently active releases, see [FEATURES.md](./FEATURES.md).
 
@@ -89,14 +91,15 @@ A MAJOR version of ICS will always be backwards compatible with the previous MAJ
 
 The following table indicates the compatibility of currently active releases:
 
-| Consumer | Provider | `v5.2.0` | `v6.1.0` | `v6.3.0` |
-| -------- | -------- | -------- | -------- | -------- |
-| `v4.0.0` |          | ✅       | ✅       | ✅ (1)   |
-| `v4.4.0` |          | ✅       | ✅       | ✅ (1)   |
-| `v4.5.0` |          | ✅       | ✅       | ✅       |
-| `v5.0.0` |          | ✅       | ✅       | ✅ (1)   |
-| `v5.2.0` |          | ✅       | ✅       | ✅ (1)   |
-| `v6.3.0` |          | ✅       | ✅       | ✅       |
+| Consumer            | Provider | `v5.2.0` | `v6.1.0` | `v6.3.0` | `v6.4.0` |
+| ------------------- | -------- | -------- | -------- | -------- | -------- |
+| `v4.0.0`            |          | ✅       | ✅       | ✅ (1)   | ✅ (1)   |
+| `v4.4.0`            |          | ✅       | ✅       | ✅ (1)   | ✅ (1)   |
+| `v4.5.0`            |          | ✅       | ✅       | ✅       | ✅ (1)   |
+| `v5.0.0`            |          | ✅       | ✅       | ✅ (1)   | ✅ (1)   |
+| `v5.2.0`            |          | ✅       | ✅       | ✅ (1)   | ✅ (1)   |
+| `v6.2.0` / `v6.3.0` |          | ✅       | ✅       | ✅       | ✅ (1)   |
+| `v6.4.0`            |          | ✅       | ✅       | ✅       | ✅       |
 
 #### Notes
 The following adjustments must be made to the CCV consumer genesis state that is obtained from the provider chain after the spawn time is reached in order for the consumer chain to start without errors.

app/consumer-democracy/app.go

@@ -689,8 +689,6 @@ func New(
 
 			consumerGenesis := consumertypes.GenesisState{}
 			appCodec.MustUnmarshalJSON(appState[consumertypes.ModuleName], &consumerGenesis)
-
-			consumerGenesis.PreCCV = true
 			app.ConsumerKeeper.InitGenesis(sdkCtx, &consumerGenesis)
 
 			app.Logger().Info("start to run module migrations...")

app/consumer/genesis.go

@@ -31,13 +31,17 @@ type GenesisState map[string]json.RawMessage
 type IcsVersion string
 
 const (
-	v4_x_x IcsVersion = "v4.x"
-	v5_x_x IcsVersion = "v5.x"
+	v4_x_x IcsVersion = "<v4.5.x" // all v4 versions < v4.5.0
+	v4_5_x IcsVersion = "v4.5.x"
+	v5_x_x IcsVersion = "v5.x"    // all v5 version
+	v6_x_x IcsVersion = "<v6.4.x" // all v6 versions < v6.4.0
 )
 
 var TransformationVersions map[string]IcsVersion = map[string]IcsVersion{
-	"v4.x": v4_x_x,
-	"v5.x": v5_x_x,
+	"<v4.5.x": v4_x_x,
+	"v4.5.x":  v4_5_x,
+	"v5.x":    v5_x_x,
+	"<v6.4.x": v6_x_x,
 }
 
 // Remove a parameter from a JSON object
@@ -56,7 +60,7 @@ func removeParameterFromParams(params json.RawMessage, param string) (json.RawMe
 // Transformation of consumer genesis content as it is exported by provider version >= v6.2.x
 // to a format supported by consumer chains version with either SDK v0.47 and ICS < v4.5.0 or SDK v0.50 and ICS < v6.2.0
 // This transformation removes the 'consumer_id' parameter from the 'params' field introduced in ICS v6.2.x
-func transformToV5(jsonRaw []byte, ctx client.Context) (json.RawMessage, error) {
+func removeConsumerID(jsonRaw []byte, ctx client.Context) (json.RawMessage, error) {
 	srcConGen := types.ConsumerGenesisState{}
 	err := ctx.Codec.UnmarshalJSON(jsonRaw, &srcConGen)
 	if err != nil {
@@ -100,7 +104,8 @@ func transformGenesis(ctx client.Context, targetVersion IcsVersion, jsonRaw []by
 
 	switch targetVersion {
 	case v4_x_x, v5_x_x:
-		newConsumerGenesis, err = transformToV5(jsonRaw, ctx)
+		newConsumerGenesis, err = removeConsumerID(jsonRaw, ctx)
+	// TODO: in addition, remove both `connection_id` and `preCCV` fields if target is v4_5_x or v6_x_x
 	default:
 		err = fmt.Errorf("unsupported target version '%s'. Run %s --help",
 			targetVersion, version.AppName)
@@ -165,17 +170,17 @@ func NewDefaultGenesisState(cdc codec.JSONCodec) GenesisState {
 func GetConsumerGenesisTransformCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "transform [-to version] genesis-file",
-		Short: "Transform CCV consumer genesis data exported to a specific target format",
+		Short: "Transform consumer module genesis data exported to a specific target format",
 		Long: strings.TrimSpace(
 			fmt.Sprintf(`
-Transform the consumer genesis data exported from a provider version v5.x v6.x to a specified consumer target version.
+Transform the consumer genesis data exported from a provider version >= v6.3.x to a specified consumer target version.
 The result is printed to STDOUT.
 
 Note: Content to be transformed is not the consumer genesis file itself but the exported content from provider chain which is used to patch the consumer genesis file!
 
 Example:
 $ %s transform /path/to/ccv_consumer_genesis.json
-$ %s --to v2.x transform /path/to/ccv_consumer_genesis.json
+$ %s --to v5.x transform /path/to/ccv_consumer_genesis.json
 `, version.AppName, version.AppName),
 		),
 		Args: cobra.RangeArgs(1, 2),