Cache fast-path quote solutions in the driver

[AryanGodara]

Description

Fast-path (out-of-competition) execution reuses a quote's solution to settle the matching order during an exclusivity window instead of running a full auction. For that the driver must keep the solution it computes at quote time (rn /quote discards it). Now we cache the fast-path quote solution in the driver, keyed by (auction_id, solution_id), and usesthose ids on the quote response so a later settle can find it.

Why cache the solution and not a ready Settlement: a quote runs against an unsigned order, so a submittable settlement can't be encoded/simulated until the real signed order exists at settle time. (tried this, goes beyond scope of the PR 🤔 )

Changes

• add a quote_solutions cache to Competition (CachedQuoteSolution { auction, solution }) + cache_quote_solution(): no simulation, bounded like the settlements deque.
• /quote caches the solution when the quote is fast-path and the request carries an auctionId, and echoes solutionId + auctionId on the response.
• /quote request accepts auctionId; the handler now passes the whole Competition to Order::quote (was just &risk_detector) so it can reach the cache — the risk-detector filtering is unchanged.
• add openApi docs and fix the request flag name fastPath → enableFastPath to match the code.

Out of scope / follow-ups:

• Orderbook allocating auctionId from the shared auctions sequence and sending it in the /quote request (BE-56) — not included; the driver accepts the id but nothing supplies one yet
• Fast-path settle path: read the cache, re-encode against the real signed order, submit (BE-57 / quote-reuse fork)
• Observer/accounting for fast-path settlements (BE-61)

Related Issues

BE-58

Follow-ups: BE-56, BE-57, BE-61.

[linear-code]

BE-58

[github-actions]

Reminder: Please consider backward compatibility when modifying the API specification.
If breaking changes are unavoidable, ensure:

• You explicitly pointed out breaking changes.
• You communicate the changes to affected teams (at least Frontend team and SAFE team).
• You provide proper versioning and migration mechanisms.

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Caused by:

• crates/driver/openapi.yml

[claude]

Claude finished @AryanGodara's task in 2m 7s —— View job

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PR Review: Cache fast-path quote solutions in the driver

• Read changed files & understand the change
• Review domain logic (competition cache, quote.rs)
• Review API DTOs & openapi
• Review tests

Overall this is a clean, well-scoped change and the code reads well. Caching the solution (not a Settlement) is the right call given the unsigned quote order, the eviction/locking mirrors the existing settlements deque, the API renaming fastPath → enableFastPath is a doc fix (not a real break), and the request/response DTOs, openapi, and tests all line up consistently.

One point worth revisiting — posted inline:

• Cache eviction bound is mis-sized for quotes (competition/mod.rs:558): reusing max_solutions_to_propose() * MAX_CONCURRENT_AUCTIONS (=5) from the settlements cache doesn't map to quote cadence; a cached fast-path solution could be evicted before its /settle arrives in the exclusivity window. Non-blocking since the settle path (BE-57) isn't wired up yet, but worth sizing against expected fast-path quote volume (or a time-based expiry) before it lands.

Nothing else stood out — the fast-path/auction_id gating in quote.rs, the Quote::try_new borrow change, and the serde skip_serializing_if on the new response fields are all correct.