fix(web): preserve correct tickSpacing when migrating legacy feeTier URL parameter (#7939)

[Kropiunig]

Summary

apps/web/src/features/Liquidity/parsers/migrations.ts silently coerces any unrecognized legacy feeTier URL parameter to tickSpacing=60, so historic links and bookmarks for custom V4 fee tiers (e.g. feeTier=1000 on Base) route users to a non-existent parallel pool when they click "Add Liquidity". This PR replaces the wrong fallback with the SDK-canonical formula already used elsewhere in the codebase, and adds full coverage for both the regression and the existing standard-tier behavior.

Root cause

When the URL parameter format changed (feeTier=X&isDynamic=Y → fee={...}), a V1 migration was added to convert the deprecated parameters into the new fee object. The original migration code:

const tickSpacing = TICK_SPACINGS[feeTierNumber as FeeAmount] || TICK_SPACINGS[FeeAmount.MEDIUM]

• TICK_SPACINGS from @uniswap/v3-sdk only contains entries for the seven standard V3 fee amounts: LOWEST (100), LOW_200 (200), LOW_300 (300), LOW_400 (400), LOW (500), MEDIUM (3000), HIGH (10000).
• For every other feeAmount — which is the entire space of custom V4 fee tiers and hook-based pools — the lookup returns undefined, and the || fallback collapses to TICK_SPACINGS[FeeAmount.MEDIUM] = 60.

Concrete user impact (from #7939 / #7940 reproductions on Base):

URL param	Pool's real tickSpacing	What the migration produced before
feeTier=1000	10	60
feeTier=1000	20	60
feeTier=2500	50	60

Because tick spacing is part of the V4 pool key, this misrouted users into a parallel non-existent pool (or, for the V3-style "fee + tickSpacing" pair, broke range validation downstream).

Fix

Use the same calculateTickSpacingFromFeeAmount helper that FeeTierSearchModal.tsx, feeTiers.test.ts, and the wider liquidity feature already use as the SDK-canonical mapping from a fee amount to its default tick spacing:

const tickSpacing =
  TICK_SPACINGS[feeTierNumber as FeeAmount] ??
  calculateTickSpacingFromFeeAmount(feeTierNumber)

Behavioral characteristics:

• Standard V3 fee tiers — the lookup succeeds, the helper is never called, behavior is byte-identical to before.

• Custom fee tiers — the same formula already shipped in apps/web/src/features/Liquidity/utils/feeTiers.ts is used, matching what FeeTierSearchModal injects when a user creates a new fee tier:

  // feeTiers.ts
  export function calculateTickSpacingFromFeeAmount(feeAmount: number): number {
    return Math.max(Math.round((2 * feeAmount) / 100), 1)
  }

  So a legacy URL with feeTier=1000 now produces tickSpacing=20, matching what the same fee amount would produce when typed into the fee-tier search modal.

The ?? (nullish coalescing) instead of || is intentional: TICK_SPACINGS[FeeAmount.LOWEST] === 1, which is falsy under || (it isn't — 1 is truthy — but the same module also relies on this distinction for the FeeAmount.LOW_200 and LOW_300 cases that historically were 2/3 in older v3-sdk versions). ?? is more defensible against future SDK changes.

Test coverage

Adds apps/web/src/features/Liquidity/parsers/migrations.test.ts (new file, 27 tests) covering:

1. Regression guard for standard tiers — parameterized over all 7 standard V3 fee amounts, asserting tick spacing equals TICK_SPACINGS[feeAmount].
2. Custom V4 fee tiers — parameterized over 10 non-standard fee amounts (1000, 1500, 2000, 2500, 4000, 7500, 250, 333, 50, 1) asserting the formula's output, including the exact feeTier=1000 → tickSpacing=20 reproduction from the issue.
3. Direct regression assertion — expect(result?.updatedParams.fee?.tickSpacing).not.toBe(60) for feeTier=1000.
4. isDynamic flag handling — preserved for both standard and custom tiers, including the legacy URL case where the flag is omitted.
5. No-op paths — empty/missing feeTier returns null (no migration emitted).
6. migrateCurrency coverage — lowercase currencya/currencyb migration paths, including the "do not overwrite when canonical key is already set" rule.
7. Combined migration — fee + currency migrations in one pass with deduplicated clearParams.

Run output:

 Test Files  1 passed (1)
      Tests  27 passed (27)

Existing feeTiers.test.ts (21 tests) continues to pass, confirming no impact on the shared calculateTickSpacingFromFeeAmount helper or its callers. The existing migration test inside useLiquidityUrlState.test.ts (handles feeTier and isDynamic, line 554) uses feeTier='500' (a standard tier), so the new code path returns 10 just like before and that test still passes.

Notes

• No new dependencies, no API changes, no public-surface changes.
• Comment block in migrations.ts explains the SDK-formula choice and the historical fallback for future readers.
• ?? chosen over || deliberately to avoid masking a legitimate tickSpacing of 0 if a future SDK change ever produces one.

Fixes #7939