params, core: add binary transition registry + UBT transition-tree end time

Introduce `params.BinaryTransitionRegistryAddress` (0x1622...1622), the
system contract that exposes MPT-to-binary transition state via fixed
storage slots (started, conversion progress, ended, base root).

Add `ChainConfig.UBTTransitionEndTime *uint64` and the
`UBTTransitionActive(num, time)` helper. While UBT is active and the
header time is below the configured end (or no end is configured), state
access is wrapped in a TransitionTrie that overlays the binary trie on
the frozen MPT base; once headers cross this timestamp, the wrapper is
dropped. Mirrors the threshold semantics of TerminalTotalDifficulty.

Surface the new field in `ChainConfig.String` and the description
banner, and add `ChainOverrides.OverrideUBTTransitionEnd` so the value
can be patched at startup alongside `OverrideUBT`.

No behaviour change yet: callers are introduced in the following commits.

core/genesis.go

@@ -276,10 +276,11 @@ func (e *GenesisMismatchError) Error() string {
 
 // ChainOverrides contains the changes to chain config.
 type ChainOverrides struct {
-	OverrideOsaka *uint64
+	OverrideOsaka            *uint64
-	OverrideBPO1  *uint64
+	OverrideBPO1             *uint64
-	OverrideBPO2  *uint64
+	OverrideBPO2             *uint64
-	OverrideUBT   *uint64
+	OverrideUBT              *uint64
+	OverrideUBTTransitionEnd *uint64
 }
 
 // apply applies the chain overrides on the supplied chain config.
@@ -299,6 +300,9 @@ func (o *ChainOverrides) apply(cfg *params.ChainConfig) error {
 	if o.OverrideUBT != nil {
 		cfg.UBTTime = o.OverrideUBT
 	}
+	if o.OverrideUBTTransitionEnd != nil {
+		cfg.UBTTransitionEndTime = o.OverrideUBTTransitionEnd
+	}
 	return cfg.CheckConfigForkOrder()
 }
 

params/config.go

@@ -468,6 +468,15 @@ type ChainConfig struct {
 	AmsterdamTime *uint64 `json:"amsterdamTime,omitempty"` // Amsterdam switch time (nil = no fork, 0 = already on amsterdam)
 	UBTTime       *uint64 `json:"ubtTime,omitempty"`       // UBT switch time (nil = no fork, 0 = already on UBT)
 
+	// UBTTransitionEndTime is the timestamp at which the MPT-to-binary
+	// transition tree is no longer applied. While UBT is active and the
+	// timestamp is below this value (or nil), state access is wrapped in a
+	// TransitionTrie that overlays the binary trie on the frozen MPT base.
+	// Once headers reach this time, the transition wrapper is dropped and
+	// state is read directly from the binary trie. nil = wrapper stays on
+	// indefinitely. Mirrors the threshold semantics of TerminalTotalDifficulty.
+	UBTTransitionEndTime *uint64 `json:"ubtTransitionEndTime,omitempty"`
+
 	// TerminalTotalDifficulty is the amount of total difficulty reached by
 	// the network that triggers the consensus upgrade.
 	TerminalTotalDifficulty *big.Int `json:"terminalTotalDifficulty,omitempty"`
@@ -598,6 +607,9 @@ func (c *ChainConfig) String() string {
 	if c.UBTTime != nil {
 		result += fmt.Sprintf(", UBTTime: %v", *c.UBTTime)
 	}
+	if c.UBTTransitionEndTime != nil {
+		result += fmt.Sprintf(", UBTTransitionEndTime: %v", *c.UBTTransitionEndTime)
+	}
 	result += "}"
 	return result
 }
@@ -693,6 +705,9 @@ func (c *ChainConfig) Description() string {
 	if c.UBTTime != nil {
 		banner += fmt.Sprintf(" - UBT:                         @%-10v blob: (%s)\n", *c.UBTTime, c.BlobScheduleConfig.UBT)
 	}
+	if c.UBTTransitionEndTime != nil {
+		banner += fmt.Sprintf(" - UBT transition tree ends:    @%-10v\n", *c.UBTTransitionEndTime)
+	}
 	banner += fmt.Sprintf("\nAll fork specifications can be found at https://ethereum.github.io/execution-specs/src/ethereum/forks/\n")
 	return banner
 }
@@ -871,6 +886,17 @@ func (c *ChainConfig) IsUBT(num *big.Int, time uint64) bool {
 	return c.IsLondon(num) && isTimestampForked(c.UBTTime, time)
 }
 
+// UBTTransitionActive reports whether state access at the given block number
+// and time should still be wrapped in a TransitionTrie (binary overlay on top
+// of the frozen MPT base). It is true when UBT is active and either no end
+// time is configured or the block is still before the configured end time.
+func (c *ChainConfig) UBTTransitionActive(num *big.Int, time uint64) bool {
+	if !c.IsUBT(num, time) {
+		return false
+	}
+	return c.UBTTransitionEndTime == nil || time < *c.UBTTransitionEndTime
+}
+
 // IsUBTGenesis checks whether the verkle fork is activated at the genesis block.
 //
 // Verkle mode is considered enabled if the verkle fork time is configured,

params/protocol_params.go

@@ -222,6 +222,16 @@ var (
 	// EIP-7251 - Increase the MAX_EFFECTIVE_BALANCE
 	ConsolidationQueueAddress = common.HexToAddress("0x0000BBdDc7CE488642fb579F8B00f3a590007251")
 	ConsolidationQueueCode    = common.FromHex("3373fffffffffffffffffffffffffffffffffffffffe1460d35760115f54807fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff1461019a57600182026001905f5b5f82111560685781019083028483029004916001019190604d565b9093900492505050366060146088573661019a573461019a575f5260205ff35b341061019a57600154600101600155600354806004026004013381556001015f358155600101602035815560010160403590553360601b5f5260605f60143760745fa0600101600355005b6003546002548082038060021160e7575060025b5f5b8181146101295782810160040260040181607402815460601b815260140181600101548152602001816002015481526020019060030154905260010160e9565b910180921461013b5790600255610146565b90505f6002555f6003555b5f54807fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff141561017357505f5b6001546001828201116101885750505f61018e565b01600190035b5f555f6001556074025ff35b5f5ffd")
+
+	// BinaryTransitionRegistryAddress is the system contract that exposes the
+	// MPT-to-binary transition state via storage slots:
+	//   slot 0 = transition started flag
+	//   slot 1 = address of the last translated account
+	//   slot 2 = hash of the last translated storage slot
+	//   slot 3 = "storage processed" flag
+	//   slot 4 = transition ended flag
+	//   slot 5 = frozen MPT base root
+	BinaryTransitionRegistryAddress = common.HexToAddress("0x1622162216221622162216221622162216221622")
 )
 
 // System log events.