Auto-mining failures are swallowed, allowing submission success without required mining pass

[roninjin10]

Summary

In auto mining mode, submission handlers ignore all errors from the mining pass and still return a tx hash success response.

Why this matters

Contract semantics define auto mode as an immediate mining pass on accepted executable submission, and runtime failures should map to runtime rejection (no result hash). Swallowing mining errors can report success even when the auto-mining step failed.

Contract anchors

• docs/specs/json-rpc-contract.md:877-880
  • auto mode trigger is accepted submission and effect is immediate single-block mining pass.
• docs/specs/json-rpc-contract.md:607-610
  • runtime rejection returns error (no tx hash result).

Evidence

Both submission paths suppress mining errors:

• src/rpc/handlers/tx_submission.zig:118-120
• src/rpc/handlers/tx_submission.zig:447-449

if (rt.mining_mode == .auto) {
    automine(allocator, rt, indexes) catch {};
}
return .{ .value = .{ .bytes = tx_hash } };

automine is fallible (allocation/state/block-seal/index writes):

• src/rpc/handlers/tx_submission.zig:466-619

Errors from these paths are currently dropped and cannot surface to RPC callers.

Suggested scope

1. Do not suppress automine errors in submission handlers.
2. Distinguish validation errors (-32602) from runtime mining failures (-32603) at handler boundary.
3. Add regression coverage where a forced mining failure in auto mode returns runtime error and does not return a success hash.