Backport release/v6.7: Bound block reference parsing depth

[seidroid]

Backport of #4030 to release/v6.7.

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Aug 27, 2026, 2:57 PM

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.34%. Comparing base (b117536) to head (6ce2194).

Files with missing lines	Patch %	Lines
cmd/frozen-rpc-router/router.go	80.48%	4 Missing and 4 partials ⚠️
cmd/frozen-rpc-router/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v6.7    #4035      +/-   ##
================================================
- Coverage         61.34%   60.34%   -1.01%     
================================================
  Files              2163     2064      -99     
  Lines            188757   177173   -11584     
================================================
- Hits             115792   106912    -8880     
+ Misses            62256    60491    -1765     
+ Partials          10709     9770     -939     

Flag	Coverage Δ
sei-chain-pr	60.63% <80.00%> (?)
sei-db	69.80% <ø> (ø)
sei-db-state-db	?

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

Files with missing lines	Coverage Δ
cmd/frozen-rpc-router/config.go	80.95% <100.00%> (+1.46%)	⬆️
cmd/frozen-rpc-router/main.go	0.00% <0.00%> (ø)
cmd/frozen-rpc-router/router.go	64.21% <80.48%> (+0.44%)	⬆️

... and 99 files with indirect coverage changes

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[cursor]

PR Summary

Low Risk
Small, localized hardening of RPC request parsing with a safe default; routing behavior only changes for abnormally deep nested block references.

Overview
Adds a configurable cap on how deeply the frozen RPC router unwraps nested EIP-1898-style {"blockNumber": ...} block parameters when choosing live vs frozen upstreams.

--max-block-reference-depth (default 16) is wired through config into the router; non-positive values are rejected at startup. parseBlockReference is now a router method that iterates up to that limit instead of recursing without bound; references nested one level beyond the limit resolve as unknown (empty reference), which keeps routing on the live node rather than spinning on pathological JSON.

Tests cover flag parsing, rejection of zero depth, and behavior at exactly the limit vs one level over.

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[seidroid]

The automated review did not complete; see the failing AI Review check for details.