diff --git a/docs/VALIDATION.md b/docs/VALIDATION.md
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index 0000000..b072d2b
--- /dev/null
+++ b/docs/VALIDATION.md
@@ -0,0 +1,219 @@
+# Site comparison validation
+
+Manual checklist for comparing **Jumbled Doubles Enhanced** (this repo) against the upstream site [jumbleddoubles.com](https://jumbleddoubles.com/) (source: [panathea/pickleball-shuffler](https://github.com/panathea/pickleball-shuffler)).
+
+Use this document before release to confirm upstream parity and to verify fork-only features (fixed pairs, stronger diversity scheduling).
+
+## References
+
+| | URL / path | Notes |
+|---|------------|-------|
+| **Upstream (baseline)** | https://jumbleddoubles.com/ | Production reference for layout, copy, and core flows |
+| **Enhanced clone (local)** | `yarn dev` → http://localhost:3000 | This fork |
+| **Architecture** | [docs/PLAN.md](./PLAN.md) | Feature design and issue map |
+| **Automated tests** | `yarn test:ci` | Algorithm + diversity + fixed-pair coverage in `test/heuristics.spec.tsx` |
+
+## What was implemented
+
+### Unchanged from upstream (parity target)
+
+- **Stack**: Next.js 13 (Pages Router), React 18, TypeScript, NextUI, Tailwind, Framer Motion
+- **State**: `useShuffler` context with `localStorage` persistence (`src/useShuffler.tsx`)
+- **Matching**: Web Worker (`src/matching/worker.ts`) → `heuristics.ts` + `PairMaker` (`ranked-matches.tsx`)
+- **Routes**: `/` (landing), `/new` (setup), `/rounds` (play)
+- **Core flows**: new game, round generation, edit players/courts/sit-outs, resume in-progress session, round pagination
+
+### Enhanced (fork-only)
+
+| Feature | Implementation | Verified by |
+|---------|----------------|-------------|
+| **Fixed pairs data model** | `fixedPairs: Team[]` in app state, persisted to `localStorage` | `src/fixedPairs.ts`, `src/useShuffler.tsx` |
+| **Fixed pairs — new game UI** | Link/unlink players on `/new` before starting | `pages/new.tsx` |
+| **Fixed pairs — in-game UI** | Pair picker in `PlayersModal` on `/rounds` | `src/PlayersModal.tsx`, `src/PlayerPairSelect.tsx` |
+| **Fixed pairs — algorithm** | Pre-formed teams before `PairMaker`; unpaired players enter partner matching | `src/matching/heuristics.ts` (`getActiveFixedTeams`, `buildSitOutUnits`) |
+| **Fixed pairs — sit-outs** | Fixed pair is an atomic sit-out unit; volunteer pulls partner | `heuristics.ts`, `test/heuristics.spec.tsx` |
+| **Fixed pairs — visuals** | Dashed border + link icon on court teams; partner label on badges | `src/TeamBadges.tsx`, `src/PlayerBadge.tsx` |
+| **Back-to-back penalty** | `BACK_TO_BACK_MATCHUP_PENALTY` (5000) for consecutive partner/opponent repeats | `src/matching/heuristics.ts` |
+| **Partner-pair counts** | Squared penalties via `partnerPairCounts` / `opponentPairCounts` | `src/matching/heuristics.ts` |
+| **Variance fairness** | `getVariance()` wired into `getNextBestRound` round selection | `src/matching/variance.tsx` |
+| **Tunable search** | `GENERATIONS = 4`, `ROUND_ATTEMPTS = 30`, `ROUND_LOOKAHEAD = 3` | `src/matching/heuristics.ts` |
+| **CI** | `yarn test:ci`, `yarn lint`, `yarn build` on push/PR | `.github/workflows/ci.yml` |
+
+---
+
+## Validation checklist
+
+Mark each item after a side-by-side or local walkthrough. **Upstream** = jumbleddoubles.com; **Enhanced** = this repo at `localhost:3000`.
+
+### A. Landing page (`/`)
+
+| # | Check | Upstream | Enhanced | Notes |
+|---|-------|----------|----------|-------|
+| A1 | Gradient hero headline (“Jumble your social play”) | ☐ | ☐ | |
+| A2 | “Why jumble?” explanatory copy | ☐ | ☐ | |
+| A3 | “Start shufflin'” CTA → `/new` | ☐ | ☐ | |
+| A4 | Compatible sports list | ☐ | ☐ | |
+| A5 | Beta / feedback section with email link | ☐ | ☐ | |
+| A6 | Navbar: curved “Jumbled Doubles” logo + Beta badge | ☐ | ☐ | CircleType on `#jumbled` (`src/Layout.tsx`) |
+| A7 | Navbar “New game” button (home only) | ☐ | ☐ | |
+| A8 | **Resume card** when `localStorage` has an active game | ☐ | ☐ | `src/ResumeActiveGame.tsx` — shows round number, links to `/rounds` |
+
+### B. New game (`/new`)
+
+| # | Check | Upstream | Enhanced | Notes |
+|---|-------|----------|----------|-------|
+| B1 | Add players via textarea (comma/newline) + add button | ☐ | ☐ | |
+| B2 | Inline edit / remove player names | ☐ | ☐ | |
+| B3 | “Reset players” confirmation modal | ☐ | ☐ | `src/ResetPlayersModal.tsx` |
+| B4 | Validation: minimum 4 players | ☐ | ☐ | |
+| B5 | Court count input with “enough players for N courts” hint | ☐ | ☐ | |
+| B6 | “Customize court names” toggle | ☐ | ☐ | |
+| B7 | Quick-set court names (1,2,3… / evens / odds) | ☐ | ☐ | |
+| B8 | Duplicate / empty court name validation | ☐ | ☐ | |
+| B9 | “Let's play!” starts game → `/rounds` | ☐ | ☐ | |
+| B10 | Pre-fills players/courts from last session | ☐ | ☐ | `localStorage` via `useShuffler` |
+| B11 | **Fixed pair link** on each unpaired player row | N/A | ☐ | Fork-only: chain icon, tap-two-to-pair |
+| B12 | **Paired players** show partner name + unlink | N/A | ☐ | Secondary highlight + `↔ Partner` label |
+| B13 | **Linking hint** while first player selected | N/A | ☐ | “Tap another player to pair…” |
+| B14 | Fixed pairs survive player rename before start | N/A | ☐ | |
+| B15 | Reset players clears fixed pairs | N/A | ☐ | |
+
+### C. Rounds view (`/rounds`)
+
+| # | Check | Upstream | Enhanced | Notes |
+|---|-------|----------|----------|-------|
+| C1 | Round header with round number | ☐ | ☐ | |
+| C2 | “Sitting out” card with player badges | ☐ | ☐ | |
+| C3 | Volunteer label on sit-out badges | ☐ | ☐ | `(volunteer)` suffix |
+| C4 | Edit sit-outs modal → regenerate current round | ☐ | ☐ | `src/SitoutsModal.tsx` |
+| C5 | Court cards: team A vs team B layout | ☐ | ☐ | `src/TeamBadges.tsx` |
+| C6 | Custom court names displayed | ☐ | ☐ | |
+| C7 | Round pagination (browse history) | ☐ | ☐ | |
+| C8 | “Jump to latest round” on older pages | ☐ | ☐ | |
+| C9 | “Start round N!” generates next round | ☐ | ☐ | Web Worker async generation |
+| C10 | Players button (count) → edit modal | ☐ | ☐ | Latest round only |
+| C11 | Courts button (count) → edit modal | ☐ | ☐ | `src/CourtsModal.tsx` |
+| C12 | **Fixed pair teams** show dashed border + link icon on court | N/A | ☐ | `TeamBadges` `aria-label="Fixed pair: …"` |
+| C13 | **Edit players modal** includes pair dropdown per player | N/A | ☐ | `PlayerPairSelect` — “No fixed partner” option |
+| C14 | Changing pairs forces round regenerate | N/A | ☐ | `pairsChanged ? true : regenerate` in `PlayersModal` |
+
+### D. Persistence and resume
+
+| # | Check | Upstream | Enhanced | Notes |
+|---|-------|----------|----------|-------|
+| D1 | Refresh `/rounds` — game state restored | ☐ | ☐ | |
+| D2 | Close tab, reopen `/` — resume card appears | ☐ | ☐ | |
+| D3 | Resume lands on correct round count | ☐ | ☐ | |
+| D4 | **Fixed pairs** restored after refresh | N/A | ☐ | `fixedPairs` in cached state |
+| D5 | Start new game clears old session appropriately | ☐ | ☐ | |
+
+### E. Edit flows (mid-session)
+
+| # | Check | Upstream | Enhanced | Notes |
+|---|-------|----------|----------|-------|
+| E1 | Add player in players modal | ☐ | ☐ | |
+| E2 | Remove (soft-delete) player | ☐ | ☐ | |
+| E3 | Regenerate vs keep history option after player edit | ☐ | ☐ | |
+| E4 | Increase/decrease courts | ☐ | ☐ | |
+| E5 | Volunteer sit-out reshuffles current round only | ☐ | ☐ | |
+| E6 | **Volunteer fixed-pair member** — partner also sits out | N/A | ☐ | See automated test “volunteer sit-out pulls fixed pair partner” |
+| E7 | **Add fixed pair mid-game** — pair stays together after regenerate | N/A | ☐ | |
+
+---
+
+## Enhanced feature validation (sample sessions)
+
+Run these on the **enhanced** site after upstream checks pass.
+
+### F. Fixed pairs — new game session
+
+**Setup:** 8 players, 2 courts. Pair Alice+Bob and Carol+Dave.
+
+| # | Check | Pass |
+|---|-------|------|
+| F1 | Alice and Bob on the same team every round (10 rounds) | ☐ |
+| F2 | Carol and Dave on the same team every round | ☐ |
+| F3 | Unpaired players still rotate partners/opponents | ☐ |
+| F4 | When 4 must sit out, each fixed pair sits out together (both in or both out) | ☐ |
+| F5 | Court display shows dashed fixed-pair styling for Alice+Bob and Carol+Dave | ☐ |
+
+### G. Fixed pairs — in-game
+
+**Setup:** Start 6-player / 1-court game with no pairs. Play 3 rounds.
+
+| # | Check | Pass |
+|---|-------|------|
+| G1 | Open players modal, pair two players, save with regenerate | ☐ |
+| G2 | Regenerated round shows pair on same team | ☐ |
+| G3 | Unlink pair in modal — subsequent regenerate allows separate teams | ☐ |
+| G4 | Removing one member of a pair drops the pair from `fixedPairs` | ☐ |
+
+### H. Diversity — no back-to-back (sample session)
+
+**Setup:** 8 players, 2 courts. Use “Start round” for **20 rounds** (enhanced uses `getNextBestRound`).
+
+| # | Check | Pass |
+|---|-------|------|
+| H1 | Scan rounds: note any **consecutive partner** repeats (same two players partnered in round N and N+1) | ☐ |
+| H2 | Scan rounds: note any **consecutive opponent** repeats | ☐ |
+| H3 | Repeats in H1/H2 only occur when unavoidable (small player count / court constraint) | ☐ |
+| H4 | Partner distribution feels even — no one stuck with same partner many rounds in a row | ☐ |
+| H5 | Sit-out rotation roughly fair across players | ☐ |
+
+**Automated equivalent:** `test/heuristics.spec.tsx` — “diversity enhancements” and “fixed pairs” suites cover H1–H3 and F1–F4 at the algorithm layer.
+
+---
+
+## Intentional UI differences
+
+Document any visual or copy differences that are **by design** (not bugs).
+
+| Area | Upstream | Enhanced | Rationale |
+|------|----------|----------|-----------|
+| Fixed pair controls on `/new` | Not present | Link icon + partner label per player | New feature (#4) |
+| Fixed pair controls in players modal | Not present | Dropdown pair selector per player | New feature (#5) |
+| Court team display | Separate badges | Dashed border + link icon for fixed pairs | Visual polish (#11) |
+| Sit-out / player badges | Plain badges | Partner name tooltip via `PairLinkIcon` when paired | Visual polish (#11) |
+| Matching quality | Baseline heuristics | Stronger penalties + variance + more search attempts | Not visible in UI; different round outcomes for same seed |
+| README “New features” | N/A | Lists fixed pairs + diversity | Docs only; upstream landing unchanged |
+
+*Add screenshots or notes below when differences need visual confirmation:*
+
+```
+[Screenshot: upstream /new vs enhanced /new with fixed pairs]
+[Screenshot: enhanced court card with fixed-pair dashed border]
+```
+
+---
+
+## Automated verification (required before merge)
+
+```bash
+yarn install
+yarn test:ci    # Jest: heuristics, variance, fixed pairs, diversity
+yarn lint       # ESLint
+yarn build      # Next.js production build
+```
+
+| Suite | What it validates |
+|-------|-------------------|
+| `test/variance.spec.tsx` | `getVariance()` ordering |
+| `test/heuristics.spec.tsx` — core | Round generation, sit-outs, preferences |
+| `test/heuristics.spec.tsx` — diversity | No avoidable back-to-back partner/opponent repeats; lower partner variance vs baseline |
+| `test/heuristics.spec.tsx` — fixed pairs | Same team, joint sit-out, mid-game pair, volunteer pulls partner |
+
+---
+
+## Sign-off
+
+| Role | Name | Date | Upstream parity (A–E) | Enhanced features (F–H) |
+|------|------|------|------------------------|-------------------------|
+| Tester | | | ☐ | ☐ |
+
+**Release criteria (from [PLAN.md](./PLAN.md)):**
+
+- [ ] All upstream flows work: new game, rounds, edit players/courts/sit-outs, resume
+- [ ] Fixed pairs always on same team; never split
+- [ ] No consecutive partner/opponent repeats unless mathematically unavoidable
+- [ ] `yarn test:ci` and `yarn build` pass
+- [ ] Visual parity with jumbleddoubles.com for core flows (enhanced adds pair UI only where noted)
diff --git a/test/heuristics.spec.tsx b/test/heuristics.spec.tsx
index 20c01c6..94e58f1 100644
--- a/test/heuristics.spec.tsx
+++ b/test/heuristics.spec.tsx
@@ -150,17 +150,22 @@ describe("calculateHeuristics()", () => {
   });
 
   test("no repeated partners before full cycle", async () => {
-    const players = sampleNames.slice(0, 9);
-    const rounds: Round[] = [];
-    for (let i = 0; i < players.length; i++) {
-      let round = await getNextBestRound(rounds, players, 3);
-      rounds.push(round);
+    const randomSpy = mockSeededRandom(1);
+    try {
+      const players = sampleNames.slice(0, 9);
+      const rounds: Round[] = [];
+      for (let i = 0; i < players.length; i++) {
+        let round = await getNextBestRound(rounds, players, 3);
+        rounds.push(round);
+      }
+      const heuristics = getHeuristics(rounds, players);
+      const numberOfMistakes = players.reduce((sum, player) => {
+        return sum + heuristics[player].playedWithCount.max - 1;
+      }, 0);
+      expect(numberOfMistakes).toBe(0);
+    } finally {
+      randomSpy.mockRestore();
     }
-    const heuristics = getHeuristics(rounds, players);
-    const numberOfMistakes = players.reduce((sum, player) => {
-      return sum + heuristics[player].playedWithCount.max - 1;
-    }, 0);
-    expect(numberOfMistakes).toBe(0);
   });
 
   test("low repeated partners after many iterations", async () => {