fix: reject unsupported custom LLMQ sizes

[thepastaclaw]

Issue being fixed

Devnet and regtest LLMQ size overrides accepted quorum sizes above 400 even though the signing protocol cannot carry them. Signing-session inventories and batched signature-share messages are capped at 400, so an oversized custom quorum could start successfully but fail later when peers exchange signing shares.

What was done

• Define Consensus::MAX_LLMQ_SIZE as the authoritative 400-member protocol maximum.
• Tie MAX_MSGS_TOTAL_BATCHED_SIGS to that shared maximum so the limits cannot drift.
• Reject oversized -llmqdevnetparams, -llmqtestparams, -llmqtestinstantsendparams, and -llmqtestplatformparams values during chain-parameter construction.
• Cover normal custom values, the inclusive 400-member boundary, and 401-member rejection for all four override paths.

This is a fail-fast configuration fix discovered while reviewing #7418. It does not change mainnet or testnet parameters, and accepted custom sizes at or below 400 retain their existing behavior.

Validation

• Full unit suite: 744 test cases passed.
• feature_llmq_signing.py: both variants passed.
• Direct startup checks: 401-member devnet/regtest overrides fail with the intended error; 400-member overrides start normally.
• git diff --check
• whitespace lint
• circular-dependency lint
• Independent pre-PR review: ship, no findings.

Scope

This intentionally adds only the missing upper bound. Existing behavior for zero, negative, or otherwise inconsistent custom size/threshold pairs is unchanged.

[thepastaclaw]

✅ Review complete (commit a54fcbe)

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: b5231da5-8843-4d2b-b6ec-2261315ae4fc

📥 Commits

Reviewing files that changed from the base of the PR and between ecf2382 and a54fcbe.

📒 Files selected for processing (4)

• src/chainparams.cpp
• src/llmq/params.h
• src/llmq/signing_shares.h
• src/test/llmq_params_tests.cpp

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Walkthrough

Adds Consensus::MAX_LLMQ_SIZE with a value of 400 and uses it for batched signature limits. Regtest and devnet LLMQ size overrides now throw std::runtime_error when exceeding this limit. Tests cover valid maximum-size overrides and rejection of larger values for both network types.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• dashpay/dash#7379: Updates related LLMQ batched-signature sizing logic.

Suggested reviewers: knst, kwvg, UdjinM6

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 28.57% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: rejecting oversized custom LLMQ sizes.
Description check	✅ Passed	The description directly matches the changeset and explains the LLMQ size limit fix and tests.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[thepastaclaw]

Code Review

Source: codex (gpt-5.6-sol, reasoning=high) — general & dash-core-commit-history lanes; sonnet5 (claude-sonnet-5, effort=high) — general & dash-core-commit-history lanes; opus (claude-opus-4-8) — general & dash-core-commit-history lanes. Final verifier: claude-sonnet-5 (verifier-sonnet5-7448-1783873850). Orchestrator (openai/gpt-5.6-sol) is orchestration-only, not a reviewer or finding source. Independently verified PR #7448 at head a54fcbe (base develop): the diff introduces Consensus::MAX_LLMQ_SIZE(400), ties MAX_MSGS_TOTAL_BATCHED_SIGS to it, and adds the upper-bound rejection to all four override paths (-llmqdevnetparams, -llmqtestparams, -llmqtestinstantsendparams, -llmqtestplatformparams) exactly as described. New unit test correctly exercises the 400-boundary and 401-rejection for all four paths. Single clean non-merge commit; message matches diff. All six native-token lanes found no defects, and independent verification confirms no in-scope issues.

Note: GitHub does not allow me to approve my own PR, so this verified clean review is posted as a COMMENT.