fix(cnight-observation): bound IDP queries by CardanoBlockWindowSize (0.22.5 backport)

[skylar-simoncelli]

Overview

Backport of #1432 to release/node-0.22.5.

The cNight observation Inherent Data Provider was querying cardano-db-sync from NextCardanoPosition all the way to the current Cardano tip on every Midnight block. For sparse assets like cNight — which appear in only a tiny fraction of Cardano outputs — this caused db-sync queries that effectively scanned the entire Cardano history on every 6-second Midnight block, blocking block import to ~0.1 bps whenever the IDP's start position fell behind tip.

CardanoBlockWindowSize already exists as runtime storage on pallet-cnight-observation (default 1000) and is already exposed via CNightObservationApi::get_cardano_block_window_size, but the IDP never actually read it. The "window" was effectively [start, ∞). This PR finishes that wiring on the 0.22.5 release branch.

Change

1. MidnightCNightObservationInherentDataProvider::new reads block_window_size from the runtime API.
2. MidnightCNightObservationDataSource::get_utxos_up_to_capacity takes a new block_window_size: u32 parameter.
3. The data source clamps the query upper bound to start + block_window_size. When tip is closer than start + window, behavior is unchanged.
4. A new db::get_block_by_block_no helper is added (uses runtime-checked sqlx::query_as so it doesn't require regenerating the offline sqlx cache).
5. The genesis-creation tool passes u32::MAX to preserve its existing full-history scan.
6. The previously-unused DEFAULT_CARDANO_BLOCK_WINDOW_SIZE constant in the IDP module is removed.

The cap on end also tightens the get_high_bounds integer-id ranges that constrain tx/tx_out/ma_tx_out/tx_in joins, so each query benefits twice from the smaller window.

🗹 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

• SQLX_OFFLINE=true cargo check -p midnight-primitives-mainchain-follower — clean
• SKIP_WASM_BUILD=1 SQLX_OFFLINE=true cargo check -p midnight-node — clean
• cargo fmt -p midnight-primitives-mainchain-follower -p midnight-node — no diff

Functional verification: replace the running node binary with this build on a node that's currently stuck at 0.0–0.1 bps with ~118s db-sync queries. Expect query latency to drop to sub-second and bps to recover to normal AURA cadence.

Please describe any additional testing aside from CI:

• Additional tests are provided (if possible)

🔱 Fork Strategy

Node-client behavior change only — the runtime API surface is unchanged (the get_cardano_block_window_size API already exists in 0.22.5 and is implemented; only its consumer changed). Old nodes continue to function with the existing slow behavior; new nodes use the bounded window.

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

Links

• main PR: fix(cnight-observation): bound IDP queries by CardanoBlockWindowSize #1432