execution/execmodule, node: remove the FCU background flush/commit path

[AskAlexSharov]

--fcu.background.commit has been default-off since it landed in #18756 (2026-01-23) and was never enabled on any branch — release/3.4, release/3.5, release/3.6 and main all carry FcuBackgroundCommit: false.

It can't be turned on as-is: FCU N returns before its commit lands, so FCU N+1 reads stale state from the DB. That is why its own TestNotificationDispatchBackgroundCommit was skipped, and why the default carries the "needs rawdb API via execctx + Coherent cache revived for rpcdaemon" note. Removing it instead of carrying a dead branch through every FCU change.

What goes

• --fcu.background.commit flag and ethconfig.Config.FcuBackgroundCommit
• the bg-commit branch in updateForkChoice: roTx/SD ownership transfer, the goroutine's PublishOverlay(nil) signal, and the extra closeModuleContext on the bad-block path
• runPostForkchoice's commit half, so it takes only initialCycle (sd, bgRoTx, finishProgressBefore, isSynced were all bg-commit-only)
• execmoduletester.WithFcuBackgroundCommit

What stays

Flush+commit is now unconditionally inline — identical to the behaviour every node already had. Background prune (--fcu.background.prune, default true) and --sync.parallel-state-flushing are untouched, as is the publishedSD fallback, which the foreground path also uses while a commit is in flight.

Tests

TestInsertBlocksWithBatchedFCU_BadBlockRecovery_{Foreground,Background} collapse into one — both cleanup branches are the same path now. The bg-commit case drops out of TestReorgBackAndForwardIntoCanonicalChain, and the skipped TestNotificationDispatchBackgroundCommit goes with the feature it covered.

go vet ./... compiles clean; ./execution/execmodule/..., ./node/ethconfig/..., ./node/cli/... pass.

The docs/site/versioned_docs/version-v3.4 copy keeps the flag on purpose — 3.4 still has it.

[Copilot]

Pull request overview

Removes the unusable FCU background commit path while preserving inline commits and optional background pruning.

Changes:

• Removes the background-commit configuration, CLI flag, and documentation.
• Simplifies fork-choice processing to always flush and commit inline.
• Removes background-commit test infrastructure and consolidates recovery coverage.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
cmd/utils/flags.go	Removes the CLI flag and config assignment.
docs/site/docs/fundamentals/configuring-erigon.mdx	Removes current-version flag documentation.
docs/site/static/llms-full.txt	Updates generated documentation content.
execution/execmodule/exec_module.go	Removes background-commit state and constructor input.
execution/execmodule/exec_module_test.go	Removes obsolete cases and consolidates recovery testing.
execution/execmodule/execmoduletester/exec_module_tester.go	Removes the tester option and configuration.
execution/execmodule/forkchoice.go	Makes commit inline and retains background pruning only.
execution/execmodule/getters.go	Updates overlay fallback terminology.
llms-full.txt	Removes the flag from consolidated documentation.
node/cli/default_flags.go	Removes the flag from default CLI registration.
node/eth/backend.go	Updates execution-module construction.
node/ethconfig/config.go	Removes the configuration field and default.
node/ethconfig/gen_config.go	Removes TOML serialization support for the field.

Files not reviewed (1)

• node/ethconfig/gen_config.go: Generated file

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