docs/superpowers/plans/2026-04-15-phase-2g-parity.md

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+# Phase 2G — Parity Harnesses
+
+> **Parent:** `2026-04-14-phase-2-online-board-master.md` (sub-plan 2G)
+> **Depends on:** 2B (URL serializer), 2F (SEO builders)
+
+## Goal
+
+Build generic, reusable parity harnesses for URL serialization and SEO output.
+Register the Online Board feature against both harnesses. Phase 3+ features
+will register their own serializers into the same framework.
+
+## Deliverables
+
+1. **URL parity harness** (`tests/parity/url/harness.ts`) — generic framework
+   for table-driven + `fast-check` property-based URL roundtrip tests.
+2. **URL parity test** (`tests/parity/url/onlineboard.test.ts`) — Online Board
+   registered against the harness, testing against fixture corpus.
+3. **URL fixture corpus** (`tests/fixtures/phase-2/url-corpus/onlineboard.json`)
+   — ~20 representative URLs covering all 6 route types.
+4. **SEO parity harness** (`tests/parity/seo/harness.ts`) — generic framework
+   for testing SEO builder output shape/completeness.
+5. **SEO parity test** (`tests/parity/seo/onlineboard.test.ts`) — Online Board
+   SEO builders registered against the harness.
+6. **`fast-check`** installed as a dev dependency.
+
+## Task list
+
+### T1 — Install `fast-check`
+
+- `pnpm add -D fast-check`
+- Verify: `pnpm typecheck`
+
+### T2 — Create URL fixture corpus
+
+- File: `tests/fixtures/phase-2/url-corpus/onlineboard.json`
+- ~20 entries covering: start, flight (with/without suffix, 3-char carrier),
+  departure (with/without time range), arrival (with/without time range),
+  route (with/without time range), details (with/without suffix).
+- Each entry: `{ url: string, expected: OnlineBoardParams }`.
+
+### T3 — URL parity harness
+
+- File: `tests/parity/url/harness.ts`
+- Exports `UrlParityConfig<T>` interface and `defineUrlParityTests<T>()`.
+- Table-driven tests: reads fixture file, for each entry asserts
+  `parse(url) === expected` and `build(expected) === url`.
+- Fuzz tests: uses `fast-check` arbitrary to generate random params,
+  asserts `parse(build(params)) deep-equals params` (roundtrip property).
+
+### T4 — Register Online Board URL parity
+
+- File: `tests/parity/url/onlineboard.test.ts`
+- Imports harness + URL serializer + fixtures.
+- Defines `fc.Arbitrary<OnlineBoardParams>` covering all 6 discriminants.
+- Calls `defineUrlParityTests(config)`.
+
+### T5 — SEO parity harness
+
+- File: `tests/parity/seo/harness.ts`
+- Exports `SeoParityConfig` interface and `defineSeoParityTests()`.
+- Tests: for each registered SEO builder call, asserts output has all required
+  fields (title, description, canonical, hreflang with 10 entries, OG tags).
+
+### T6 — Register Online Board SEO parity
+
+- File: `tests/parity/seo/onlineboard.test.ts`
+- Registers all 6 Online Board SEO builders.
+- Asserts shape correctness for each route type x 2 languages (ru, en).
+
+### T7 — Verification
+
+- `pnpm typecheck && pnpm lint && pnpm test`
+- All new tests pass. All existing tests still pass.
+
+## Exit gates
+
+- URL parity: 100% of fixture corpus passes roundtrip.
+- `fast-check` fuzz finds no roundtrip asymmetry (100 iterations default).
+- SEO parity: all 6 route types produce complete SeoHeadProps.
+- `pnpm typecheck`, `pnpm lint`, `pnpm test` green.
+- No `any` types in harness code.