task: replace unwrap() calls in genesis state decoding (PM-20204)

[m2ux]

Overview

Replace three unwrap() calls in run_node genesis state decoding with a decode_genesis_state helper that returns typed errors via sc_cli::Error::Input. This prevents the node from panicking on startup when the chain spec contains a missing, non-string, or invalid-hex genesis_state property. Adds a 256 MiB size guard against adversarial chain specs.

Addresses Least Authority audit finding Issue M (High severity).

🎫 PM-20204 📐 Engineering

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Changes

• node/src/command.rs — Extract decode_genesis_state function from inline unwrap() chain in run_node. Returns sc_cli::Result<Vec<u8>> with descriptive Error::Input messages for each failure mode (missing key, non-string value, invalid hex, oversized payload). Matches the existing error handling pattern used for seed file loading in the same module.
• Tests — 5 unit tests covering: valid hex roundtrip, empty hex edge case, missing key, non-string value, invalid hex.
• Changelog — changes/changed/fix-genesis-state-decode-panic.md

🗹 TODO before merging

• Ready

📌 Submission Checklist

• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason:
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• Updated AGENTS.md if build commands, architecture, or workflows changed
• No new todos introduced

🧪 Testing Evidence

5 new unit tests for decode_genesis_state added to node/src/command.rs:

running 9 tests
test command::tests::decode_genesis_state_invalid_hex ... ok
test command::tests::decode_genesis_state_missing_key ... ok
test command::tests::decode_genesis_state_empty_hex ... ok
test command::tests::decode_genesis_state_non_string_value ... ok
test command::tests::decode_genesis_state_valid_hex ... ok
test cfg::tests::assert_no_ignored_defaults ... ok
test cfg::tests::assert_no_ignored_cfg_presets ... ok
test cfg::tests::dev_cfg_preset_deserializes_without_errors ... ok
test cfg::tests::load_all_presets ... ok

test result: ok. 9 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Validation: cargo clippy -p midnight-node -- -D warnings (0 warnings), cargo fmt -- --check (clean).

• Additional tests are provided (if possible)

🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other:
• N/A

Links

• PM-20204 — Node Panic on Startup
• Least Authority audit finding Issue M (High severity)

[github-actions]

KICS version: v2.1.16

Category Results CRITICAL 0 HIGH 0 MEDIUM 96 LOW 12 INFO 83 TRACE 0 TOTAL 191	Metric Values Files scanned 31 Files parsed 31 Files failed to scan 0 Total executed queries 73 Queries failed to execute 0 Execution time 9