Checkpoint receive scans to subgraph head block

[garyghayrat]

Summary

This changes the Receive page checkpointing logic so subgraph-backed scans advance to the subgraph head block instead of the RPC latest block.

Why

On Base and other subgraph-dependent chains, the previous logic stored the provider latest block after a scan. If the subgraph lagged behind the RPC head, a newly indexed announcement could be skipped permanently because future scans would start after the missed block.

What changed

• fetch the subgraph head block from _meta
• support both Ponder _meta.status and legacy _meta.block.number shapes
• use that head block as the next cached lastFetchedBlock
• fall back conservatively to the prior scan checkpoint if the head-block lookup fails

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[github-actions]

Coverage after merging codex/checkpoint-scans-to-subgraph-head into master will be

83.87%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
contracts-periphery/src
UmbraBatchSend.sol	100%	100%	100%	100%
UniswapWithdrawHook.sol	100%	100%	100%	100%
umbra-js/src
ethers.ts	86.27%	100%	75%	100%
types.ts	50%	100%	0%	100%
umbra-js/src/classes
KeyPair.ts	98.54%	97.62%	100%	98.75%	248, 250
RandomNumber.ts	100%	100%	100%	100%
StealthKeyRegistry.ts	100%	100%	100%	100%
TxHistoryProvider.ts	81.48%	65%	80%	93.10%	12, 17, 20, 23, 29, 43, 48, 54, 8
Umbra.ts	82.47%	74.25%	85.37%	87%	144–145, 166, 239–240, 308, 326–329, 365–366, 397, 412, 415, 422–424, 426, 433, 436–437, 462, 462, 462, 464, 464, 464, 466, 466, 466, 466–467, 467, 467–469, 484, 484, 484–485, 489, 492, 512, 530–532, 573, 628, 632, 678, 691–692, 702–703, 717, 725–726, 756–757, 832–833, 836, 839–840, 846–848, 855, 855, 855–858, 893, 895–896, 896–897
umbra-js/src/utils
cns.ts	50%	33.33%	50%	55%	33–36, 40, 40, 40, 40, 40–41, 44–46
constants.ts	100%	100%	100%	100%
ens.ts	36.11%	25%	33.33%	40%	25–27, 35, 56–57, 57, 57–58, 63–64, 66, 70, 70, 70, 70, 70–71, 75–77
sharedSecret.ts	83.05%	72.73%	100%	87.88%	24, 27–28, 42–43, 47–48, 62, 62–63
utils.ts	71.02%	63.98%	80%	74.82%	102, 102, 1026–1027, 1039–1040, 118–120, 122–124, 130, 152–153, 179–181, 181, 181–182, 182, 182, 203, 268, 271, 276, 280, 284, 294, 306–311, 313–320, 320, 320, 320, 320, 320, 320–321, 323, 333, 347–348, 348, 348–349, 353–354, 364, 364, 364–366, 368, 384–386, 414, 437, 440, 444, 444–445, 445, 445–446, 446, 448, 452–453, 456–457, 480, 483, 483, 483–485, 515, 517–518, 527, 527, 527–528, 530, 533, 542–543, 584, 601, 601, 601, 630, 652–654, 657, 667, 679, 679, 68, 680, 685, 687–688, 69, 699–703, 716, 718, 769–770, 770, 770–772, 772, 772, 783, 94
umbra-js/test
testPrivateKeys.ts	100%	100%	100%	100%
utils.ts	100%	100%	100%	100%