fix(evmrpc): use synthetic IDs in slow-path batch to handle duplicate and null request IDs

[amir-deris]

Problem

In the slow-path (gated) handleBatch flow, mergeSeiLegacyHTTPBatch built idToIdx keyed on the original request ID echoed back by the inner server. When a batch contained multiple requests sharing the same ID — including multiple "id":null entries — the old code detected the ID collision and fell through to appendMergeFailure, replacing all responses in the batch with internal errors.

Fix

Assign a unique sequential synthetic integer ID (0, 1, 2, …) to each forwarded non-notification request before dispatching to the inner server. The inner server echoes these synthetic IDs back, so idToIdx is always collision-free regardless of duplicate or null original IDs. Original IDs are restored in the output via patchJSONRPCResponseIDIfNeeded.

Changes:

• Merge the blocked-check into the same parse loop to avoid a second pass over msgs
• Replace appendMergeFailure on duplicate inner-ID with a best-effort continue (the synthetic-ID scheme makes this unreachable in normal operation, but it's safer than a hard failure)
• Drop redundant json.RawMessage(...) casts on already-[]byte return values

Tests

• Added TestWrapSeiLegacyHTTP_BatchTwoNullIDsDifferentResults: regression test covering two "id":null requests + a notification + a unique-ID request + a blocked sei_ method in one batch — verifies correct per-slot responses and that the notification is omitted from output
• Updated existing tests to expect synthetic IDs (0, 1, …) instead of original IDs in the forwarded body

Linear

Closes PLT-282, PLT-292

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Apr 29, 2026, 9:32 AM

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.17%. Comparing base (740b2dd) to head (b03f9d1).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
evmrpc/sei_legacy_http.go	85.71%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3331      +/-   ##
==========================================
+ Coverage   59.16%   59.17%   +0.01%     
==========================================
  Files        2097     2097              
  Lines      172485   172496      +11     
==========================================
+ Hits       102053   102078      +25     
+ Misses      61570    61562       -8     
+ Partials     8862     8856       -6     

Flag	Coverage Δ
sei-chain-pr	64.56% <85.71%> (?)
sei-db	70.41% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
evmrpc/sei_legacy_http.go	80.91% <85.71%> (+0.83%)	⬆️

... and 28 files with indirect coverage changes

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[seidroid]

Created backport PR for release/v6.4:

• Backport release/v6.4: fix(evmrpc): use synthetic IDs in slow-path batch to handle duplicate and null request IDs #3333 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-3331-to-release/v6.4
git worktree add --checkout .worktree/backport-3331-to-release/v6.4 backport-3331-to-release/v6.4
cd .worktree/backport-3331-to-release/v6.4
git reset --hard HEAD^
git cherry-pick -x e47d7a2ba3c0234a84baaa8adc1a0af04665af79
git push --force-with-lease