fix(precompiles): preserve mega overrides across spec changes

[mega-putin]

Generated by engineer-agent — review carefully before merging.

Summary

Make the MegaContext precompile provider treat set_spec(OpSpecId) as a no-op so the precompile table baked at EVM construction is never rebuilt from a vanilla op spec. This preserves Mega-specific overrides like the 100k-gas KZG pricing even if upstream starts exercising set_spec on the warm transaction path, and adds a regression test to pin that behavior.

Fixes #286

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.6%. Comparing base (be4418d) to head (16f94a5).
⚠️ Report is 1 commits behind head on main.

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[mega-putin]

🔧 Pushed CI fixes.

Agent log

I fixed the `doc-impact` failure by adding the missing spec clarification to `docs/spec/evm/precompiles.md`. The page now states that Mega-specific precompile overrides must be preserved whenever an implementation refreshes its internal precompile table, and that the upstream baseline spec id alone is not enough to reconstruct the Mega table when multiple Mega specs share the same baseline.

Commit: `5fea50db378fe37531048b58ea3ee722ed0d5122`  
Message: `fix CI: document preservation of mega precompile overrides`

Verification:
- `npx prettier --write 'docs/**/*.md'`
- `npx prettier --check 'docs/**/*.md'`

[mega-putin]

Updated the PR labels accordingly.

spec:unchanged has been replaced with spec:stable, and the PR now carries:

• spec:stable
• comp:core
• api:unchanged

This matches the behavior of the change: it fixes stable-spec precompile behavior rather than leaving behavior unchanged.

[mega-putin]

Updated accordingly.

spec:unchanged has already been replaced with spec:stable, and the PR label set is now:

• spec:stable
• comp:core
• api:unchanged

That matches the intent of the change: this PR fixes stable-spec precompile behavior rather than leaving behavior unchanged.

[mega-putin]

Added comp:doc to the PR label set.

The PR now carries:

• spec:stable
• comp:core
• comp:doc
• api:unchanged

That reflects both parts of the change: the stable-spec precompile fix and the follow-up spec documentation update in docs/spec/evm/precompiles.md.

[mega-putin]

Updated already.

spec:unchanged has been replaced with spec:stable, and the PR label set now includes:

• spec:stable
• comp:core
• comp:doc
• api:unchanged

That matches the behavior of the change: this PR fixes stable-spec precompile behavior and also includes the follow-up documentation update.

[mega-putin]

No action needed here.

This is the automated Codecov coverage report. It is informational, and it already shows the relevant result for this PR:

• all modified and coverable lines are covered by tests
• project coverage remains healthy

There is no question to answer or requested change to make from this comment.

[claude]

LGTM. The fix is minimal and correct:

• The no-op on PrecompilesMap::set_spec is the right call: the table is baked at construction from MegaSpecId, and since all current Mega specs share the same OpSpecId::ISTHMUS, delegating to the upstream rebuild would silently wipe the 100k-gas KZG override.
• The comment in the code explicitly acknowledges the future-proofing caveat ("all current Mega specs"), so a developer adding a new spec will be prompted to revisit this.
• The regression test correctly pins the KZG gas cost after a set_spec call. The set_spec_for_context helper for type inference is an acceptable pattern.
• Doc addition in precompiles.md accurately captures the implementation contract.

[mega-putin]

Thanks. That matches the intent of the change.

The fix is meant to make the MegaContext runtime path explicitly preserve the Mega-selected precompile table instead of inheriting behavior from the upstream OpSpecId-keyed provider, and the regression test and spec note are there to keep that invariant visible on future dependency or spec updates.

[RealiCZ]

LGTM