commitment: eliminate BranchMerger from fold→encode→write hot path

[awskii]

Summary

Encode complete BranchData (full afterMap) instead of partial data that required a Merge step on the read path. This removes BranchMerger entirely from the hot path.

Changes

• foldBranch(): use afterMap as the encoding bitmap instead of touchMap & afterMap — encoded branch now contains all cells
• CollectUpdate() (immediate path): remove merger.Merge(prev, update) call; remove merger field and pool from BranchEncoder
• encodeDeferredUpdate() (deferred path): remove merger parameter and workerMergerPool; update all callers in ApplyDeferredBranchUpdates
• Add benchmarks: BenchmarkEncodeBranch, BenchmarkCollectUpdate_EncodeDirect

Benchmark Results (encode+merge vs encode-direct)

Cells	Old (encode+merge)	New (encode-direct)	Improvement
2	~174 ns/op	~118 ns/op	−32%
8	~454 ns/op	~404 ns/op	−11%
16	~868 ns/op	~813 ns/op	−6%

Verification

• All commitment tests pass (including deferred, concurrent, multi-step)
• make lint passes
• make erigon integration builds successfully

[Copilot]

Pull request overview

This PR optimizes the commitment trie “fold → encode → write” path by always encoding complete BranchData (all afterMap cells), eliminating the need to merge partial branch encodings with previous data.

Changes:

• Update foldBranch() to encode with bitmap = afterMap and to pass touchMap=afterMap so written BranchData is complete.
• Remove BranchMerger usage from both immediate (CollectUpdate) and deferred (encodeDeferredUpdate / ApplyDeferredBranchUpdates) encoding paths, including removing the merger pool and encoder field.
• Add benchmarks to compare encode-direct vs the prior encode+merge approach, and add a completed implementation plan doc.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
execution/commitment/hex_patricia_hashed.go	Switch branch encoding bitmap to afterMap and pass complete maps into update collection.
execution/commitment/commitment.go	Remove merger from encoder/deferred update hot paths and simplify worker pooling accordingly.
execution/commitment/commitment_bench_test.go	Add benchmarks for EncodeBranch and end-to-end encode+merge vs encode-direct comparison.
docs/plans/completed/20260413-complete-branchdata-encoding.md	Document the approach, testing strategy, and benchmark expectations/results for the change.

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[awskii]

branch works multiple steps but even wit revert of f5593e6 still have gas mismatch on it after a while

[awskii]

[WARN] [04-15|19:48:00.725]   tx gas detail                          block=10666684 txIdx=165 txHash=0xbe4964f37cf3aab6 gasUsed=50636 cumGasUsed=25911890 computedCumGas=25911890 status=1
[WARN] [04-15|19:48:00.725] [4/6 Execution] Execution failed         block=10666684 txNum=944868573 header-hash=0x39c24a34a5be5f40761d27ac6f5f0e0689810afb1e6a09a6298b2ad65733200c err="invalid block, txnIdx=166, gas used by execution: 25911890, in header: 25928990, headerNum=10666684, 39c24a34a5be5f40761d27ac6f5f0e0689810afb1e6a09a6298b2ad65733200c" isForkValidation=false
[INFO] [04-15|19:48:00.739] [4/6 Execution] serial done              in=374.961457ms buf=7.4MB/512.0MB blk=10666679 blks=1 blk/s=2 txs=0 tx/s=0 gas/s=443.44M stepsInDB=0.86 step=2418.9 alloc=7.6GB sys=15.1GB isForkValidation=false isApplyingBlocks=true
[WARN] [04-15|19:48:00.740] Cannot update chain head                 hash=0x0f311e6be6e66da2a14f18916a017f0e29dc0d9ccd18321f91e76eb0ee405ab1 err="updateForkChoice: [4/6 Execution] invalid block, txnIdx=166, gas used by execution: 25911890, in header: 25928990, headerNum=10666684, 39c24a34a5be5f40761d27ac6f5f0e0689810afb1e6a09a6298b2ad65733200c"
[WARN] [04-15|19:48:00.740] error executing clstage                  app=caplin stage=ForkChoice err="failed to compute and notify services of new fork choice: failed to run forkchoice: bad block as forkchoice"

[AskAlexSharov]

blocked by:
#20593
and
#20445