fix(router): invoke toToken.address.toLowerCase() in per-pair cache key

[thedavidmeister]

What

The per-pair throttle-cache key read toToken.address.toLowerCase without the call parens in all four RainSolverRouter query methods (getMarketPrice, tryQuote, findBestRoute, getTradeParams) and in the coupled reader prepareRouter (src/core/process/round.ts:109).

A method reference stringifies to its source code, so the key's second segment became the constant function toLowerCase() { [native code] } for every token — the key depended only on fromToken and collided across all toTokens.

BUGGY key = "0xfrom..-function toLowerCase() { [native code] }"   // same for every toToken
FIXED key = "0xfrom..-0xto.."                                     // distinct per toToken

Impact (real bug, latent)

RainSolverRouter.cache is a prefetch-throttle counter, not a result cache — the query methods always run a live Promise.all and return live results, so the collision never returned a stale route/quote/price. But the counter gates prepareRouter (skip pool-data prefetch once a pair's counter > 3). With the key collapsed to the sell token only:

• Cross-pair contamination: unrelated pairs sharing a sell token share one counter, so pair (X, Z) can push the gate past its skip threshold and cause (X, Y) to skip prefetch even though it was never warmed.
• Throttle saturates ~2x too fast: prepareRouter's (sell→buy) and (sell→native) calls collapse to the same key, double-incrementing the sell-token counter per round.

Mitigated (not catastrophic) by the newPoolCreated force-prefetch branch and the separately, correctly keyed route caches — but genuinely incorrect cross-pair behavior. Full diagnosis + probe in #445.

Fix

Add the missing () at all four router.ts sites and the coupled round.ts:109 reader (fixing only the writer would break the gate, since the reader key would stop matching the writer key).

Tests (mutation-validated)

• src/router/router.test.ts — for each of the four methods: one fromToken + two different toTokens yields two distinct cache entries (cache.size === 2, exact keys asserted). Collides to size 1 (FAILS) under the missing-() mutation.
• src/core/process/round.test.ts — a pair pre-warmed under the correctly-keyed counter skips prefetch; a different buyToken (same sellToken) still prefetches. FAILS under the round.ts missing-() mutation (prefetch wrongly runs).

Verified each new test passes with the fix and fails when the () is reverted at the corresponding site. tsc + eslint clean; full vitest unit suite green (the lone transport.test.ts flake is an environmental EADDRINUSE :9292 port clash, passes in isolation; e2e-fork is pre-existing/environmental).

Note: #443 also added tests to src/router/router.test.ts; trivial rebase if it lands first.

Closes #445

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ℹ️ Review info

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Configuration used: Organization UI

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Run ID: 04f12b5c-b4ba-4436-a782-df645b645a30

📥 Commits

Reviewing files that changed from the base of the PR and between 08492e8 and 80cf804.

📒 Files selected for processing (2)

• src/core/process/round.test.ts
• src/router/router.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-06-15-router-cache-key-fix

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[thedavidmeister]

Reviewed 80cf804: approved by maintainer; conflict resolved via merge of master (production fix already in master via #443 — this contributes the mutation-validated per-pair cache-key tests + corrected doc comments). build, unit tests, git-clean, CodeRabbit all green; the only reds are the e2e-fork suite, which is environmental (fails identically on master). Merging.

[github-actions]

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