diff --git a/BUILD-STATE.md b/BUILD-STATE.md
index 7dd0707..6a87c33 100755
--- a/BUILD-STATE.md
+++ b/BUILD-STATE.md
@@ -1,7 +1,24 @@
 # VYNDR — Build State
 
 ## Last Updated
-2026-07-10
+2026-07-11
+
+## Session S3 (a1 board, 2026-07-11) — Affiliate + Partnership Plumbing ✅
+Zero out-of-pocket; everything config-flip-ready but DISABLED/organic.
+2398 → **2439 tests** (209 suites), web build exit 0.
+- **BOOK IT deep links** — `web/src/lib/bookLinks.js` + `affiliateConfig.js`
+  (every book `enabled:false`; Impact/Partnerize param shapes documented).
+  StatStrip BOOK IT is a real anchor now (organic); scan hand-off links moved
+  to the builder. Every book anchor renders `rel="sponsored noopener noreferrer"`.
+- **Best-price marker** — `slateAdapter.detectBestBook` (≥2 books, SAME line,
+  differing prices, else null) + green dot in StatStrip; `books[]` (the grouped
+  odds rows) now threads Slate → strips instead of being discarded by pickLine.
+- **Partner refs** — `?ref=CODE` → 90d first-party `vyndr_ref` cookie
+  (first-touch, `PartnerRefCapture` in layout) → signup metadata `partner_ref`
+  → internal `GET /api/partners/report/:code` (zeros + note until the TODO
+  migration in docs/PARTNERS.md adds `user_profiles.partner_ref`; NOT run).
+- **docs/PARTNERS.md** — ref link spec, Stripe promo-code mapping convention
+  (partner code == promotion code), TODO migration SQL.
 
 ## Current Phase
 SHIP BUILD v59.0 — Overnight session: ledger team/opponent addendum,
diff --git a/CLAUDE.md b/CLAUDE.md
index 0a4ee14..d64ffb7 100755
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -801,6 +801,32 @@ phased plan in the Session-57 conversation / BUILD-STATE Next section).
   amber / VALUE green / red = STALE-or-miss only), mono data surfaces, and
   schedule-derived waiting copy. Keep them green.
 
+## Affiliate + Partner Plumbing (A1 S3 — non-obvious)
+- **Every sportsbook link goes through `web/src/lib/bookLinks.js`**
+  (`buildBookLink` → `{url, tracking}`; unknown book → null). The affiliate
+  layer is `web/src/lib/affiliateConfig.js` — ALL books `enabled:false` (no
+  program approved); flipping a book + filling params produces tracked URLs
+  with NO component changes. Empty param values are SKIPPED (a half-filled
+  config degrades to organic, never a fabricated id). Anchors MUST render
+  `rel={BOOK_LINK_REL}` ("sponsored noopener noreferrer") — tests assert it.
+- **Best-price dot honesty rule:** `slateAdapter.detectBestBook(rows, side,
+  refLine)` returns a book ONLY when ≥2 books post the SAME line for the side
+  and prices differ — never compare odds across different lines, never mark a
+  lone price "best". The per-book rows reach the browser as `lines[]` on each
+  grouped prop; `Slate.groupByGame` now threads them as `books` on PropRowProp
+  (pickLine still picks the single displayed line).
+- **Partner attribution:** `?ref=CODE` → `vyndr_ref` cookie (90d, FIRST-touch,
+  `lib/partnerRef.js` + `PartnerRefCapture` in layout) → `signUp` metadata
+  `partner_ref` → internal `GET /api/partners/report/:code`. The
+  `user_profiles.partner_ref` column does NOT exist yet — the endpoint returns
+  zeros + note until the TODO migration in `docs/PARTNERS.md` runs (metadata
+  lands in auth.users.raw_user_meta_data, which PostgREST can't query). OAuth
+  signups carry no metadata (known gap). Partner code == Stripe promotion code,
+  verbatim (docs/PARTNERS.md §3).
+- **Worktree build gotcha:** `web/node_modules` isn't shared into git worktrees
+  and Turbopack REJECTS a symlink pointing outside the project root — use
+  `cp -al` (hardlink copy) from the main repo's web/node_modules.
+
 ## Active Skills
 - vyndr-voice (all user-facing output)
 - prop-analysis (grading methodology)
diff --git a/docs/PARTNERS.md b/docs/PARTNERS.md
new file mode 100644
index 0000000..8e88df4
--- /dev/null
+++ b/docs/PARTNERS.md
@@ -0,0 +1,119 @@
+# VYNDR Partner + Affiliate Plumbing (A1 Session 3)
+
+Everything here ships DISABLED / organic by default. No affiliate program is
+approved yet; nothing spends money and no link carries tracking params until an
+operator flips config. Data semantics apply to attribution too — the report
+endpoint returns zeros before it returns invented numbers.
+
+## 1. Partner ref links
+
+A partner shares:
+
+```
+https://vyndr.app/?ref=CODE
+```
+
+- `CODE` — A-Z 0-9 dash underscore, max 32 chars, case-insensitive
+  (canonicalized to UPPERCASE everywhere).
+- On first visit `PartnerRefCapture` (mounted in the layout) sets the
+  first-party cookie `vyndr_ref` for 90 days (SameSite=Lax, Path=/).
+- Attribution is FIRST TOUCH: an existing cookie is never overwritten.
+- On email/password signup, `AuthContext.signUp` forwards the cookie value
+  into Supabase signup metadata as `partner_ref`
+  (`auth.users.raw_user_meta_data.partner_ref`).
+- Known limitation: OAuth signups (Google, etc.) do not carry signup
+  metadata — those signups are not attributed yet.
+
+## 2. Partner report endpoint (internal)
+
+```
+GET /api/partners/report/:code
+Header: x-internal-key: $VYNDR_INTERNAL_KEY
+```
+
+Response:
+
+```json
+{ "ok": true, "code": "CODE", "signups": 0, "conversions": 0, "mrr_attributed": 0 }
+```
+
+- `signups` — user_profiles rows with `partner_ref = CODE`
+- `conversions` — those currently `subscription_status = 'active'` on a paid tier
+- `mrr_attributed` — sum of the real monthly price per active profile
+  (analyst 19.99 / 14.99 founder, desk 49.99 / 34.99 founder)
+
+### TODO migration (documented, NOT run)
+
+`user_profiles` has no `partner_ref` column today, and signup metadata lives in
+`auth.users.raw_user_meta_data`, which PostgREST cannot query. Until the
+migration below is applied, the endpoint returns zeros with a `note`. Once
+applied, real numbers flow with no code change.
+
+```sql
+-- TODO migration: 021_partner_ref.sql (do not run until reviewed)
+alter table public.user_profiles
+  add column if not exists partner_ref text;
+
+create index if not exists idx_user_profiles_partner_ref
+  on public.user_profiles(partner_ref)
+  where partner_ref is not null;
+
+-- Copy the signup metadata field on profile creation
+-- (extend the existing handle_new_user trigger):
+create or replace function public.handle_new_user()
+returns trigger as $$
+begin
+  insert into public.user_profiles (id, email, partner_ref)
+  values (
+    new.id,
+    new.email,
+    upper(nullif(new.raw_user_meta_data->>'partner_ref', ''))
+  )
+  on conflict (id) do nothing;
+  return new;
+end;
+$$ language plpgsql security definer;
+
+-- One-time backfill for signups that predate the column:
+update public.user_profiles p
+set partner_ref = upper(u.raw_user_meta_data->>'partner_ref')
+from auth.users u
+where u.id = p.id
+  and p.partner_ref is null
+  and nullif(u.raw_user_meta_data->>'partner_ref', '') is not null;
+```
+
+Note: migration 004 (`referral_codes` / `referral_conversions`) is the separate
+USER-referral system (codes owned by auth users). Partner codes are external
+strings and deliberately do not depend on those tables.
+
+## 3. Stripe promo-code mapping convention
+
+One code, three systems, zero lookup tables:
+
+- The partner's ref code IS their Stripe promotion code, verbatim.
+  Partner "HOOPSPOD" → `?ref=HOOPSPOD` link → Stripe promotion code
+  `HOOPSPOD` on checkout.
+- Codes are created in Stripe as promotion codes on a shared partner coupon;
+  set promotion code metadata `partner: <CODE>` so Stripe reporting can be
+  cross-checked against `/api/partners/report/:code`.
+- Cookie-attributed signups and promo-code redemptions are reconciled by the
+  shared code string — a signup that used the promo but arrived without the
+  cookie still attributes through Stripe's side.
+- Founder codes (VYNDR, BETONBLK, `FOUNDER_CODE_EXPIRY` in stripeService) are
+  NOT partner codes — do not issue a partner code that collides with a founder
+  code.
+
+## 4. Sportsbook affiliate config (BOOK IT deep links)
+
+- `web/src/lib/bookLinks.js` builds every sportsbook deep link (StatStrip
+  BOOK IT + scan hand-off). Organic shape: `https://{host}/?search={player}`.
+- `web/src/lib/affiliateConfig.js` is the single flip point: per book
+  `{ enabled: false, params: {} }`. Param shapes (Impact: irclickid /
+  sharedid / wpsrc; Partnerize-style: btag / afid / siteid) are documented in
+  that file. Empty param values are skipped — a half-filled config degrades to
+  organic, never a fabricated id.
+- Every book anchor renders `rel="sponsored noopener noreferrer"`
+  (`BOOK_LINK_REL`) — required for affiliate compliance, harmless organic.
+- BetRivers accepts an optional two-letter `state` for its state subdomain
+  (`mi.betrivers.com`); anything else falls back to `www`.
diff --git a/specs/a1-s3-affiliate-partner-plumbing.md b/specs/a1-s3-affiliate-partner-plumbing.md
new file mode 100644
index 0000000..90fd41c
--- /dev/null
+++ b/specs/a1-s3-affiliate-partner-plumbing.md
@@ -0,0 +1,72 @@
+# A1 Session 3 — Affiliate + Partnership Plumbing
+
+## Operating constraints
+- ZERO out-of-pocket. No affiliate program is approved yet — everything ships
+  config-flip-ready but DISABLED / organic by default.
+- Data semantics: never fabricate market values. A "best price" claim renders
+  only when genuinely multiple books post the same line — absent beats wrong.
+- No exclamation points in any copy (VOICE v1.1).
+
+## 1. BOOK IT deep-link builder
+- `web/src/lib/bookLinks.js` (CommonJS, unit-testable)
+  - `SUPPORTED_BOOKS`: draftkings, fanduel, betmgm, caesars, betrivers
+    (hosts sourced from the existing SPORTSBOOKS list in scan/page.tsx +
+    lib/books.js brand map).
+  - `buildBookLink({ book, player, sport, state? }, config?) → { url, tracking } | null`
+    - Unknown book → null (absent beats wrong).
+    - Organic base: `https://{host}/?search={player}` (existing deep-link shape).
+    - Affiliate layer: reads `web/src/lib/affiliateConfig.js` — per book
+      `{ enabled: false, params: {} }` with Impact/Partnerize-style param
+      shapes documented in comments (irclickid / sharedid / afid / btag).
+    - `tracking: true` only when the book is enabled AND at least one
+      non-empty param was appended. Disabled → clean organic link.
+  - `BOOK_LINK_REL = 'sponsored noopener noreferrer'` — every book anchor
+    renders this rel.
+- Wiring:
+  - `StatStrip.tsx` BookItTeaser → real `<a>` deep link (best-price book when
+    known, else the prop's book, else DraftKings). Organic until config flips.
+  - `scan/page.tsx` sportsbook hand-off anchors → `buildBookLink` +
+    `BOOK_LINK_REL` (replaces the local SPORTSBOOKS/deepLink pair).
+
+## 2. Best-line highlight (cheap version)
+- Finding (documented in the session report): the grouped odds proxy already
+  ships per-book rows to the browser as `lines[]` per player+stat;
+  `Slate.groupByGame`/`pickLine` collapse to ONE line and discard the rest.
+- Ship: thread `books` (the raw `lines[]`) onto each PropRowProp;
+  `slateAdapter.detectBestBook(rows, side, refLine)` returns
+  `{ book, odds }` ONLY when ≥2 books post the SAME line for the side and
+  prices differ; `buildPlayerStripsFromProps` attaches `bestBook` + `book`
+  to each strip prop; StatStrip renders a subtle signal-green dot
+  (one meaning: best available price).
+
+## 3. Partner ref system
+- (a) `web/src/lib/partnerRef.js` (CommonJS) — parse `?ref=CODE`, sanitize
+  (A–Z 0–9 - _, ≤32, uppercased), first-party cookie `vyndr_ref` (90d,
+  SameSite=Lax, Path=/), first-touch (never overwrites an existing cookie).
+  `components/vyndr/PartnerRefCapture.tsx` mounted in the layout
+  (GlobalHosts pattern).
+- (b) `src/routes/partners.js` — `GET /api/partners/report/:code` behind
+  `requireInternalAuth` → `{ signups, conversions, mrr_attributed }` read
+  from `user_profiles` filtered by `partner_ref`. The column does NOT exist
+  yet: the endpoint degrades to zeros + a note, and the TODO migration is
+  documented in docs/PARTNERS.md (NOT run).
+- (c) Signup: `AuthContext.signUp` forwards the `vyndr_ref` cookie into
+  Supabase signup metadata as `partner_ref`.
+- (d) `docs/PARTNERS.md` — Stripe promo-code mapping convention + the
+  TODO migration.
+
+## Acceptance criteria
+- All book links organic by default; flipping `enabled` + params in
+  affiliateConfig produces a tracked URL with the params appended.
+- Best-price dot never renders on single-book or unequal-line data.
+- `?ref=CODE` first visit sets `vyndr_ref` for 90 days; signup metadata
+  carries `partner_ref`; report endpoint 401s without the internal key.
+- Full `npx jest` green; `cd web && npx next build` exit 0.
+
+## Test plan
+- tests/unit/bookLinks.test.js — organic default, enabled param shapes,
+  aliases, betrivers state, unknown book, rel constant + source assertions.
+- tests/unit/slateAdapterBestBook.test.js — detectBestBook honesty rules +
+  strip attachment.
+- tests/unit/partnerRef.test.js — sanitize/parse/cookie/first-touch.
+- tests/unit/partnersRoute.test.js — report math + internal-auth mount.
diff --git a/src/app.js b/src/app.js
index 5d0f905..eacb9e7 100644
--- a/src/app.js
+++ b/src/app.js
@@ -187,6 +187,9 @@ app.use('/api/content', contentRoutes);
 // the public surface; the Next.js admin route proxies through with
 // the key kept server-side.
 app.use('/api/internal', internalRoutes);
+// A1 S3 — partner attribution report. Internal-key gated (router-level
+// requireInternalAuth); no Next proxy on purpose — never browser-facing.
+app.use('/api/partners', require('./routes/partners'));
 
 // Session 10 — Sentry's Express error handler catches uncaught
 // errors from every route mounted above. Must come AFTER routes but
diff --git a/src/routes/partners.js b/src/routes/partners.js
new file mode 100644
index 0000000..a08eef8
--- /dev/null
+++ b/src/routes/partners.js
@@ -0,0 +1,117 @@
+'use strict';
+
+/**
+ * Partner attribution report (A1 Session 3).
+ *
+ * GET /api/partners/report/:code — internal-only (requireInternalAuth,
+ * same key as the snapshot pipeline; never browser-reachable, no Next
+ * proxy on purpose). Returns per-partner attribution:
+ *
+ *   { ok, code, signups, conversions, mrr_attributed, note? }
+ *
+ * Data source: public.user_profiles filtered by `partner_ref` — the
+ * code a signup carried in its metadata (set by the web PartnerRefCapture
+ * → AuthContext.signUp flow).
+ *
+ * IMPORTANT — the `partner_ref` column does NOT exist on user_profiles
+ * yet. Signup metadata lands in auth.users.raw_user_meta_data, which
+ * PostgREST can't query. Until the TODO migration in docs/PARTNERS.md
+ * is applied (adds the column + copies it from the signup metadata in
+ * handle_new_user), the select errors and this endpoint HONESTLY
+ * degrades to zeros with a `note` — it never fabricates attribution.
+ * Once the migration runs, real numbers flow with no code change here.
+ *
+ * MRR attribution uses the REAL tier prices (founder_pricing-aware) on
+ * currently-active paid profiles. It is monthly recurring revenue at
+ * today's price book — not lifetime value, not a projection.
+ */
+
+const express = require('express');
+const { requireInternalAuth } = require('../middleware/internalAuth');
+const { getSupabaseServiceClient } = require('../utils/supabase');
+
+const router = express.Router();
+
+router.use(requireInternalAuth({ loopbackOnly: false }));
+
+// Tier price book (matches stripeService / pricing page).
+const TIER_MRR = {
+  analyst: { standard: 19.99, founder: 14.99 },
+  desk: { standard: 49.99, founder: 34.99 },
+};
+
+/** Same convention as web/src/lib/partnerRef.js — A-Z 0-9 - _, ≤32, uppercase. */
+function sanitizePartnerCode(raw) {
+  const s = String(raw == null ? '' : raw).trim().toUpperCase();
+  if (!s || s.length > 32) return null;
+  return /^[A-Z0-9_-]+$/.test(s) ? s : null;
+}
+
+/**
+ * Pure report math over user_profiles rows
+ * ({ tier, subscription_status, founder_pricing }).
+ *   signups        — every profile attributed to the code
+ *   conversions    — profiles currently on an active paid tier
+ *   mrr_attributed — sum of those profiles' monthly price (founder-aware)
+ */
+function buildPartnerReport(rows) {
+  const list = Array.isArray(rows) ? rows : [];
+  let conversions = 0;
+  let mrr = 0;
+  for (const r of list) {
+    if (!r) continue;
+    const tier = String(r.tier || 'free').toLowerCase();
+    const active = String(r.subscription_status || '') === 'active';
+    const prices = TIER_MRR[tier];
+    if (!prices || !active) continue;
+    conversions += 1;
+    mrr += r.founder_pricing === true ? prices.founder : prices.standard;
+  }
+  return {
+    signups: list.length,
+    conversions,
+    mrr_attributed: Math.round(mrr * 100) / 100,
+  };
+}
+
+// Injectable for tests (no network / no Supabase env needed).
+let _getClient = getSupabaseServiceClient;
+function _setClientForTests(fn) {
+  _getClient = typeof fn === 'function' ? fn : getSupabaseServiceClient;
+}
+
+router.get('/report/:code', async (req, res) => {
+  const code = sanitizePartnerCode(req.params.code);
+  if (!code) {
+    return res.status(400).json({ ok: false, error: 'invalid partner code' });
+  }
+  try {
+    const supabase = _getClient();
+    const { data, error } = await supabase
+      .from('user_profiles')
+      .select('tier, subscription_status, founder_pricing')
+      .eq('partner_ref', code);
+
+    if (error) {
+      // Column not migrated yet (docs/PARTNERS.md TODO) — zeros, never invented.
+      return res.json({
+        ok: true,
+        code,
+        signups: 0,
+        conversions: 0,
+        mrr_attributed: 0,
+        note: 'partner_ref is not queryable yet — apply the TODO migration in docs/PARTNERS.md to activate attribution',
+      });
+    }
+    return res.json({ ok: true, code, ...buildPartnerReport(data) });
+  } catch (err) {
+    const message = err && err.message ? err.message : String(err);
+    console.error('[partners/report] failed:', message);
+    return res.status(500).json({ ok: false, error: message });
+  }
+});
+
+module.exports = router;
+module.exports.sanitizePartnerCode = sanitizePartnerCode;
+module.exports.buildPartnerReport = buildPartnerReport;
+module.exports._setClientForTests = _setClientForTests;
diff --git a/tests/unit/bookItTeaser.test.js b/tests/unit/bookItTeaser.test.js
index 666fd2a..fbeec23 100644
--- a/tests/unit/bookItTeaser.test.js
+++ b/tests/unit/bookItTeaser.test.js
@@ -1,20 +1,26 @@
-// Session 52 — Push-to-Book "Coming Soon" teaser (source-asserted).
+// Session 52 shipped BOOK IT as a "coming soon" teaser. A1 Session 3
+// made it a REAL sportsbook deep link (organic until affiliateConfig
+// flips a book on). GradeResultCard's PUSH-TO-BOOK (account linking /
+// bet-slip push) remains a genuine teaser — that feature is unbuilt.
 
 const fs = require('fs');
 const path = require('path');
 const WEB = path.join(__dirname, '..', '..', 'web', 'src');
 const read = (rel) => fs.readFileSync(path.join(WEB, rel), 'utf8');
 
-describe('BOOK IT teaser', () => {
-  it('StatStrip renders the "BOOK IT" teaser on graded props', () => {
+describe('BOOK IT deep link (was the S52 teaser)', () => {
+  it('StatStrip renders BOOK IT as a real anchor built by bookLinks', () => {
     const src = read('components/vyndr/StatStrip.tsx');
     expect(src).toContain('BookItTeaser');
     expect(src).toContain('BOOK IT ⟶');
-    expect(src).toContain('Push-to-Book coming soon');
     expect(src).toContain('<BookItTeaser p={p} />');
+    expect(src).toContain('buildBookLink({ book: target, player, sport })');
+    expect(src).toContain('rel={BOOK_LINK_REL}');
+    // the dead-span teaser copy is gone
+    expect(src).not.toContain('Push-to-Book coming soon');
   });
 
-  it('GradeResultCard renders "PUSH-TO-BOOK · COMING SOON"', () => {
+  it('GradeResultCard still renders the honest "PUSH-TO-BOOK · COMING SOON" teaser', () => {
     const src = read('components/vyndr/GradeResultCard.tsx');
     expect(src).toContain('PUSH-TO-BOOK · COMING SOON');
     expect(src).toContain('Connect DraftKings, FanDuel, BetMGM');
diff --git a/tests/unit/bookLinks.test.js b/tests/unit/bookLinks.test.js
new file mode 100644
index 0000000..da6387c
--- /dev/null
+++ b/tests/unit/bookLinks.test.js
@@ -0,0 +1,114 @@
+// A1 Session 3 — BOOK IT deep-link builder. Organic by default; the
+// affiliate layer only fires when a book is explicitly enabled with
+// real params. Every anchor renders rel="sponsored noopener noreferrer".
+
+const fs = require('fs');
+const path = require('path');
+const { buildBookLink, resolveBookId, SUPPORTED_BOOKS, BOOK_LINK_REL } = require('../../web/src/lib/bookLinks');
+const { AFFILIATE_CONFIG } = require('../../web/src/lib/affiliateConfig');
+
+const WEB = path.join(__dirname, '..', '..', 'web', 'src');
+const read = (rel) => fs.readFileSync(path.join(WEB, rel), 'utf8');
+
+describe('buildBookLink — organic by default', () => {
+  it('builds a clean organic link for every supported book (default config)', () => {
+    for (const b of SUPPORTED_BOOKS) {
+      const out = buildBookLink({ book: b.id, player: 'Aaron Judge', sport: 'mlb' });
+      expect(out).not.toBeNull();
+      expect(out.tracking).toBe(false);
+      expect(out.url).toContain(`https://${b.host}/`);
+      expect(out.url).toContain('search=Aaron+Judge');
+      // no affiliate params leak into an organic link
+      expect(out.url).not.toMatch(/irclickid|sharedid|btag|afid|siteid/);
+    }
+  });
+
+  it('ships EVERY book disabled in the checked-in config', () => {
+    for (const b of SUPPORTED_BOOKS) {
+      expect(AFFILIATE_CONFIG[b.id]).toBeDefined();
+      expect(AFFILIATE_CONFIG[b.id].enabled).toBe(false);
+    }
+  });
+
+  it('resolves book aliases (DK / DraftKings / draftkings)', () => {
+    expect(resolveBookId('DK')).toBe('draftkings');
+    expect(resolveBookId('DraftKings')).toBe('draftkings');
+    expect(resolveBookId('fanduel')).toBe('fanduel');
+    expect(resolveBookId('MGM')).toBe('betmgm');
+    expect(resolveBookId('CZR')).toBe('caesars');
+    expect(resolveBookId('BR')).toBe('betrivers');
+  });
+
+  it('returns null for unknown books and missing player (absent beats wrong)', () => {
+    expect(buildBookLink({ book: 'bovada', player: 'Aaron Judge' })).toBeNull();
+    expect(buildBookLink({ book: 'prizepicks', player: 'Aaron Judge' })).toBeNull();
+    expect(buildBookLink({ book: 'draftkings', player: '' })).toBeNull();
+    expect(buildBookLink({})).toBeNull();
+  });
+
+  it('betrivers routes by two-letter state subdomain, else www', () => {
+    const mi = buildBookLink({ book: 'betrivers', player: 'Judge', state: 'MI' });
+    expect(mi.url).toContain('https://mi.betrivers.com/');
+    const bad = buildBookLink({ book: 'betrivers', player: 'Judge', state: 'Michigan' });
+    expect(bad.url).toContain('https://www.betrivers.com/');
+    const none = buildBookLink({ book: 'betrivers', player: 'Judge' });
+    expect(none.url).toContain('https://www.betrivers.com/');
+  });
+});
+
+describe('buildBookLink — affiliate layer (config-flip)', () => {
+  const enabled = {
+    draftkings: { enabled: true, params: { irclickid: 'IRC123', sharedid: 'vyndr', wpsrc: 'vyndr-slate' } },
+    betmgm: { enabled: true, params: { btag: 'BT-42', afid: '' } },
+    caesars: { enabled: false, params: { btag: 'SHOULD-NOT-APPEAR' } },
+  };
+
+  it('appends Impact-style params and reports tracking when enabled', () => {
+    const out = buildBookLink({ book: 'draftkings', player: 'Aaron Judge' }, enabled);
+    expect(out.tracking).toBe(true);
+    expect(out.url).toContain('irclickid=IRC123');
+    expect(out.url).toContain('sharedid=vyndr');
+    expect(out.url).toContain('wpsrc=vyndr-slate');
+    expect(out.url).toContain('search=Aaron+Judge');
+  });
+
+  it('skips empty param values (never emits a fabricated id)', () => {
+    const out = buildBookLink({ book: 'betmgm', player: 'Judge' }, enabled);
+    expect(out.tracking).toBe(true);
+    expect(out.url).toContain('btag=BT-42');
+    expect(out.url).not.toContain('afid=');
+  });
+
+  it('enabled with ONLY empty params stays organic (tracking false)', () => {
+    const out = buildBookLink({ book: 'fanduel', player: 'Judge' }, { fanduel: { enabled: true, params: { irclickid: ' ' } } });
+    expect(out.tracking).toBe(false);
+    expect(out.url).not.toContain('irclickid');
+  });
+
+  it('disabled book with params configured stays organic', () => {
+    const out = buildBookLink({ book: 'caesars', player: 'Judge' }, enabled);
+    expect(out.tracking).toBe(false);
+    expect(out.url).not.toContain('SHOULD-NOT-APPEAR');
+  });
+});
+
+describe('rel="sponsored noopener noreferrer" on every book anchor', () => {
+  it('exports the exact rel contract', () => {
+    expect(BOOK_LINK_REL).toBe('sponsored noopener noreferrer');
+  });
+
+  it('StatStrip BOOK IT anchor uses buildBookLink + BOOK_LINK_REL', () => {
+    const src = read('components/vyndr/StatStrip.tsx');
+    expect(src).toContain('buildBookLink');
+    expect(src).toContain('rel={BOOK_LINK_REL}');
+    expect(src).toContain('BOOK IT ⟶');
+  });
+
+  it('scan page hand-off anchors use buildBookLink + BOOK_LINK_REL', () => {
+    const src = read('app/scan/page.tsx');
+    expect(src).toContain('SUPPORTED_BOOKS');
+    expect(src).toContain('rel={BOOK_LINK_REL}');
+    // the old hardcoded organic builder is gone
+    expect(src).not.toContain('const deepLink =');
+  });
+});
diff --git a/tests/unit/partnerRef.test.js b/tests/unit/partnerRef.test.js
new file mode 100644
index 0000000..5ffcdb7
--- /dev/null
+++ b/tests/unit/partnerRef.test.js
@@ -0,0 +1,94 @@
+// A1 Session 3 — partner ref capture: ?ref=CODE → first-party vyndr_ref
+// cookie (90d, first-touch) → signup metadata partner_ref.
+
+const fs = require('fs');
+const path = require('path');
+const {
+  REF_COOKIE,
+  sanitizeRefCode,
+  parseRefFromSearch,
+  readRefCookie,
+  buildRefCookie,
+  captureRef,
+} = require('../../web/src/lib/partnerRef');
+
+const WEB = path.join(__dirname, '..', '..', 'web', 'src');
+const read = (rel) => fs.readFileSync(path.join(WEB, rel), 'utf8');
+
+describe('sanitizeRefCode', () => {
+  it('uppercases and accepts A-Z 0-9 - _', () => {
+    expect(sanitizeRefCode('hoopspod')).toBe('HOOPSPOD');
+    expect(sanitizeRefCode(' the-wire_22 ')).toBe('THE-WIRE_22');
+  });
+  it('rejects empty, too-long, and unsafe codes', () => {
+    expect(sanitizeRefCode('')).toBeNull();
+    expect(sanitizeRefCode(null)).toBeNull();
+    expect(sanitizeRefCode('a'.repeat(33))).toBeNull();
+    expect(sanitizeRefCode('bad code')).toBeNull();
+    expect(sanitizeRefCode('<script>')).toBeNull();
+    expect(sanitizeRefCode('a;b')).toBeNull();
+  });
+});
+
+describe('parseRefFromSearch / readRefCookie / buildRefCookie', () => {
+  it('parses ?ref= out of a search string', () => {
+    expect(parseRefFromSearch('?ref=hoopspod&utm_source=x')).toBe('HOOPSPOD');
+    expect(parseRefFromSearch('?utm_source=x')).toBeNull();
+    expect(parseRefFromSearch('')).toBeNull();
+  });
+  it('builds a 90-day first-party cookie string', () => {
+    const c = buildRefCookie('hoopspod');
+    expect(c).toContain(`${REF_COOKIE}=HOOPSPOD`);
+    expect(c).toContain(`Max-Age=${90 * 24 * 60 * 60}`);
+    expect(c).toContain('Path=/');
+    expect(c).toContain('SameSite=Lax');
+    expect(c).not.toContain('Secure');
+    expect(buildRefCookie('hoopspod', { secure: true })).toContain('; Secure');
+    expect(buildRefCookie('bad code')).toBeNull();
+  });
+  it('reads the cookie back out of a document.cookie string', () => {
+    expect(readRefCookie('foo=1; vyndr_ref=HOOPSPOD; bar=2')).toBe('HOOPSPOD');
+    expect(readRefCookie('foo=1; bar=2')).toBeNull();
+    expect(readRefCookie('')).toBeNull();
+  });
+});
+
+describe('captureRef — first touch wins', () => {
+  const fakeWindow = (search, cookie = '') => {
+    const doc = { cookie };
+    return { location: { search, protocol: 'https:' }, document: doc };
+  };
+
+  it('sets the cookie on a first visit with ?ref=', () => {
+    const w = fakeWindow('?ref=hoopspod');
+    expect(captureRef(w)).toBe('HOOPSPOD');
+    expect(w.document.cookie).toContain('vyndr_ref=HOOPSPOD');
+    expect(w.document.cookie).toContain('; Secure'); // https origin
+  });
+
+  it('does NOT overwrite an existing ref cookie (first touch)', () => {
+    const w = fakeWindow('?ref=newpartner', 'vyndr_ref=ORIGINAL');
+    expect(captureRef(w)).toBeNull();
+    expect(w.document.cookie).toBe('vyndr_ref=ORIGINAL');
+  });
+
+  it('no-ops without a ref param or without a window', () => {
+    const w = fakeWindow('?utm_source=x');
+    expect(captureRef(w)).toBeNull();
+    expect(w.document.cookie).toBe('');
+    expect(captureRef(null)).toBeNull();
+  });
+});
+
+describe('wiring (source-asserted)', () => {
+  it('PartnerRefCapture is mounted in the layout (GlobalHosts pattern)', () => {
+    const layout = read('app/layout.tsx');
+    expect(layout).toContain('<PartnerRefCapture />');
+    expect(layout).toContain("from '@/components/vyndr/PartnerRefCapture'");
+  });
+  it('signUp forwards the cookie as partner_ref signup metadata', () => {
+    const auth = read('contexts/AuthContext.tsx');
+    expect(auth).toContain('readRefCookie(document.cookie)');
+    expect(auth).toContain('partner_ref: partnerRef');
+  });
+});
diff --git a/tests/unit/partnersRoute.test.js b/tests/unit/partnersRoute.test.js
new file mode 100644
index 0000000..d8b7104
--- /dev/null
+++ b/tests/unit/partnersRoute.test.js
@@ -0,0 +1,99 @@
+// A1 Session 3 — internal partner attribution report.
+// Pure report math + route behavior with an injected Supabase client.
+
+const express = require('express');
+const request = require('supertest');
+
+const partnersRouter = require('../../src/routes/partners');
+const { sanitizePartnerCode, buildPartnerReport, _setClientForTests } = partnersRouter;
+
+const KEY = 'test-internal-key';
+
+function makeApp() {
+  const app = express();
+  app.use('/api/partners', partnersRouter);
+  return app;
+}
+
+describe('sanitizePartnerCode', () => {
+  it('uppercases and accepts the cookie convention (A-Z 0-9 - _, ≤32)', () => {
+    expect(sanitizePartnerCode('hoopspod')).toBe('HOOPSPOD');
+    expect(sanitizePartnerCode('THE-WIRE_22')).toBe('THE-WIRE_22');
+  });
+  it('rejects unsafe input', () => {
+    expect(sanitizePartnerCode('a b')).toBeNull();
+    expect(sanitizePartnerCode('a'.repeat(33))).toBeNull();
+    expect(sanitizePartnerCode('')).toBeNull();
+    expect(sanitizePartnerCode("x';drop")).toBeNull();
+  });
+});
+
+describe('buildPartnerReport', () => {
+  it('counts signups, active paid conversions, and founder-aware MRR', () => {
+    const rows = [
+      { tier: 'free', subscription_status: 'none', founder_pricing: false },
+      { tier: 'analyst', subscription_status: 'active', founder_pricing: false }, // 19.99
+      { tier: 'analyst', subscription_status: 'active', founder_pricing: true }, // 14.99
+      { tier: 'desk', subscription_status: 'active', founder_pricing: false }, // 49.99
+      { tier: 'desk', subscription_status: 'canceled', founder_pricing: false }, // not active
+    ];
+    expect(buildPartnerReport(rows)).toEqual({ signups: 5, conversions: 3, mrr_attributed: 84.97 });
+  });
+  it('empty / bad input → zeros', () => {
+    expect(buildPartnerReport([])).toEqual({ signups: 0, conversions: 0, mrr_attributed: 0 });
+    expect(buildPartnerReport(null)).toEqual({ signups: 0, conversions: 0, mrr_attributed: 0 });
+  });
+});
+
+describe('GET /api/partners/report/:code', () => {
+  const OLD_KEY = process.env.VYNDR_INTERNAL_KEY;
+  beforeAll(() => { process.env.VYNDR_INTERNAL_KEY = KEY; });
+  afterAll(() => {
+    if (OLD_KEY === undefined) delete process.env.VYNDR_INTERNAL_KEY;
+    else process.env.VYNDR_INTERNAL_KEY = OLD_KEY;
+    _setClientForTests(null);
+  });
+
+  const fakeClient = (result) => () => ({
+    from: () => ({ select: () => ({ eq: () => Promise.resolve(result) }) }),
+  });
+
+  it('401s without the internal key', async () => {
+    const res = await request(makeApp()).get('/api/partners/report/HOOPSPOD');
+    expect(res.status).toBe(401);
+  });
+
+  it('400s an invalid code', async () => {
+    const res = await request(makeApp())
+      .get('/api/partners/report/bad%20code')
+      .set('x-internal-key', KEY);
+    expect(res.status).toBe(400);
+  });
+
+  it('returns real attribution when the partner_ref column exists', async () => {
+    _setClientForTests(fakeClient({
+      data: [
+        { tier: 'analyst', subscription_status: 'active', founder_pricing: true },
+        { tier: 'free', subscription_status: 'none', founder_pricing: false },
+      ],
+      error: null,
+    }));
+    const res = await request(makeApp())
+      .get('/api/partners/report/hoopspod')
+      .set('x-internal-key', KEY);
+    expect(res.status).toBe(200);
+    expect(res.body).toEqual({ ok: true, code: 'HOOPSPOD', signups: 2, conversions: 1, mrr_attributed: 14.99 });
+  });
+
+  it('degrades to zeros + note when the column is not migrated yet', async () => {
+    _setClientForTests(fakeClient({ data: null, error: { message: 'column user_profiles.partner_ref does not exist' } }));
+    const res = await request(makeApp())
+      .get('/api/partners/report/HOOPSPOD')
+      .set('x-internal-key', KEY);
+    expect(res.status).toBe(200);
+    expect(res.body.signups).toBe(0);
+    expect(res.body.conversions).toBe(0);
+    expect(res.body.mrr_attributed).toBe(0);
+    expect(res.body.note).toContain('docs/PARTNERS.md');
+  });
+});
diff --git a/tests/unit/slateAdapterBestBook.test.js b/tests/unit/slateAdapterBestBook.test.js
new file mode 100644
index 0000000..7742574
--- /dev/null
+++ b/tests/unit/slateAdapterBestBook.test.js
@@ -0,0 +1,107 @@
+// A1 Session 3 — best available price detection. Honesty rules: a best
+// price only exists when ≥2 books post the SAME line for the side and
+// their prices differ. Absent beats wrong.
+
+const { detectBestBook, buildPlayerStripsFromProps } = require('../../web/src/lib/slateAdapter');
+
+describe('detectBestBook', () => {
+  const rows = [
+    { book: 'draftkings', line: 1.5, over_odds: -115, under_odds: -105 },
+    { book: 'fanduel', line: 1.5, over_odds: -105, under_odds: -115 },
+    { book: 'betmgm', line: 1.5, over_odds: -120, under_odds: 100 },
+  ];
+
+  it('picks the best over price at the shared line', () => {
+    const out = detectBestBook(rows, 'over', 1.5);
+    expect(out).toEqual({ book: 'fanduel', odds: -105 });
+  });
+
+  it('picks the best under price independently', () => {
+    const out = detectBestBook(rows, 'under', 1.5);
+    expect(out).toEqual({ book: 'betmgm', odds: 100 });
+  });
+
+  it('returns null for a single book (a lone price is not "best")', () => {
+    expect(detectBestBook([rows[0]], 'over', 1.5)).toBeNull();
+    expect(detectBestBook([], 'over', 1.5)).toBeNull();
+    expect(detectBestBook(null, 'over', 1.5)).toBeNull();
+  });
+
+  it('returns null when all books post the identical price', () => {
+    const flat = [
+      { book: 'draftkings', line: 1.5, over_odds: -110 },
+      { book: 'fanduel', line: 1.5, over_odds: -110 },
+    ];
+    expect(detectBestBook(flat, 'over', 1.5)).toBeNull();
+  });
+
+  it('returns null when books only post DIFFERENT lines (odds are not comparable)', () => {
+    const split = [
+      { book: 'draftkings', line: 1.5, over_odds: -200 },
+      { book: 'fanduel', line: 2.5, over_odds: 120 },
+    ];
+    expect(detectBestBook(split, 'over', 1.5)).toBeNull();
+    expect(detectBestBook(split, 'over', 2.5)).toBeNull();
+  });
+
+  it('without a reference line, compares at the modal line', () => {
+    const mixed = [
+      { book: 'draftkings', line: 1.5, over_odds: -115 },
+      { book: 'fanduel', line: 1.5, over_odds: -105 },
+      { book: 'betmgm', line: 2.5, over_odds: 200 },
+    ];
+    expect(detectBestBook(mixed, 'over')).toEqual({ book: 'fanduel', odds: -105 });
+  });
+
+  it('ignores rows with missing book / line / side odds', () => {
+    const dirty = [
+      { book: 'draftkings', line: 1.5, over_odds: -115 },
+      { book: null, line: 1.5, over_odds: -100 },
+      { book: 'fanduel', line: 1.5, over_odds: null },
+      { book: 'betmgm', over_odds: -105 },
+    ];
+    expect(detectBestBook(dirty, 'over', 1.5)).toBeNull();
+  });
+});
+
+describe('buildPlayerStripsFromProps — bestBook attachment', () => {
+  const books = [
+    { book: 'draftkings', line: 1.5, over_odds: -115, under_odds: -105 },
+    { book: 'fanduel', line: 1.5, over_odds: -105, under_odds: -115 },
+  ];
+
+  it('attaches bestBook + book to a graded prop (graded side)', () => {
+    const props = [{ player: 'Aaron Judge', stat_type: 'total_bases', line: 1.5, direction: 'over', book: 'draftkings', books }];
+    const gradeIndex = {
+      'aaron judge|total_bases': {
+        player: 'Aaron Judge', stat_type: 'total_bases', line: 1.5,
+        direction: 'over', grade: 'A', gradedAt: { line: 1.5, odds: -115, timestamp: new Date().toISOString() },
+      },
+    };
+    const strips = buildPlayerStripsFromProps(props, gradeIndex, {});
+    expect(strips).toHaveLength(1);
+    const p = strips[0].props[0];
+    expect(p.book).toBe('draftkings');
+    expect(p.bestBook).toEqual({ book: 'fanduel', odds: -105 });
+  });
+
+  it('attaches bestBook on awaiting props too (still real market data)', () => {
+    const props = [{ player: 'Aaron Judge', stat_type: 'total_bases', line: 1.5, direction: 'under', book: 'draftkings', books }];
+    const strips = buildPlayerStripsFromProps(props, {}, {});
+    const p = strips[0].props[0];
+    expect(p.awaiting).toBe(true);
+    expect(p.bestBook).toEqual({ book: 'draftkings', odds: -105 });
+  });
+
+  it('leaves bestBook null when only one book posted the prop', () => {
+    const props = [{ player: 'Aaron Judge', stat_type: 'total_bases', line: 1.5, direction: 'over', book: 'draftkings', books: [books[0]] }];
+    const strips = buildPlayerStripsFromProps(props, {}, {});
+    expect(strips[0].props[0].bestBook).toBeNull();
+  });
+
+  it('leaves bestBook null when props carry no books array (legacy shape)', () => {
+    const props = [{ player: 'Aaron Judge', stat_type: 'total_bases', line: 1.5, direction: 'over', book: 'draftkings' }];
+    const strips = buildPlayerStripsFromProps(props, {}, {});
+    expect(strips[0].props[0].bestBook).toBeNull();
+  });
+});
diff --git a/tests/unit/vyndrCoreScreens.test.js b/tests/unit/vyndrCoreScreens.test.js
index 99c3ff7..f4704bf 100644
--- a/tests/unit/vyndrCoreScreens.test.js
+++ b/tests/unit/vyndrCoreScreens.test.js
@@ -150,8 +150,12 @@ describe('Phase D — scan + landing wiring', () => {
     expect(src).toContain('mapScanToGradeResult');
     expect(src).not.toContain("from '@/components/GradeCard'");
   });
-  it('scan keeps sportsbook deep-links safe (noopener noreferrer)', () => {
-    expect(read('app/scan/page.tsx')).toContain('noopener noreferrer');
+  it('scan keeps sportsbook deep-links safe (A1 S3: BOOK_LINK_REL = sponsored noopener noreferrer)', () => {
+    const src = read('app/scan/page.tsx');
+    expect(src).toContain('rel={BOOK_LINK_REL}');
+    // the constant itself carries noopener noreferrer (+ sponsored)
+    const { BOOK_LINK_REL } = require('../../web/src/lib/bookLinks');
+    expect(BOOK_LINK_REL).toContain('noopener noreferrer');
   });
   it('landing mounts the ClaimMeter', () => {
     expect(read('app/page.tsx')).toContain('ClaimMeter');
diff --git a/web/src/app/layout.tsx b/web/src/app/layout.tsx
index 84e5871..6704605 100644
--- a/web/src/app/layout.tsx
+++ b/web/src/app/layout.tsx
@@ -9,6 +9,7 @@ import Footer from '@/components/Footer';
 import AuthGate from '@/components/AuthGate';
 import HashRedirect from '@/components/vyndr/HashRedirect';
 import GlobalHosts from '@/components/vyndr/GlobalHosts';
+import PartnerRefCapture from '@/components/vyndr/PartnerRefCapture';
 // Session 50 — the Parlay Lab supersedes the legacy ParlayTray.
 import ParlayPanel from '@/components/vyndr/ParlayPanel';
 import BottomTabBar from '@/components/BottomTabBar';
@@ -156,6 +157,8 @@ export default async function RootLayout({ children }: { children: React.ReactNo
               <SentryInit />
               {/* Session 38 — prefs apply + paywall/checkout/prefs globals (§9/§10/§12) */}
               <GlobalHosts />
+              {/* A1 S3 — first-visit ?ref=CODE → vyndr_ref cookie (90d, first-touch) */}
+              <PartnerRefCapture />
             </ParlayProvider>
             </ExplainModeProvider>
           </AuthProvider>
diff --git a/web/src/app/scan/page.tsx b/web/src/app/scan/page.tsx
index c98f596..379abc6 100644
--- a/web/src/app/scan/page.tsx
+++ b/web/src/app/scan/page.tsx
@@ -17,6 +17,7 @@ import {
   trackUpgradeClicked,
 } from '@/lib/analytics';
 import { getHeadshotUrl, PLAYER_SILHOUETTE, type HeadshotSport } from '@/lib/playerHeadshot';
+import { buildBookLink, SUPPORTED_BOOKS, BOOK_LINK_REL } from '@/lib/bookLinks';
 
 type Sport = 'NBA' | 'MLB' | 'WNBA';
 
@@ -103,15 +104,8 @@ const SPORT_ACCENT: Record<Sport, string> = {
   WNBA: '#FFB347',
 };
 
-// Sportsbook deep-links — preserved from the legacy GradeCard so the new
-// design keeps the book hand-off. target=_blank + noopener,noreferrer.
-const SPORTSBOOKS = [
-  { id: 'draftkings', label: 'DraftKings', host: 'sportsbook.draftkings.com' },
-  { id: 'fanduel', label: 'FanDuel', host: 'sportsbook.fanduel.com' },
-  { id: 'betmgm', label: 'BetMGM', host: 'sports.betmgm.com' },
-  { id: 'caesars', label: 'Caesars', host: 'sportsbook.caesars.com' },
-];
-const deepLink = (host: string, player: string) => `https://${host}/?search=${encodeURIComponent(player)}`;
+// Sportsbook deep-links — A1 S3: built by lib/bookLinks (organic until the
+// affiliate config flips a book on). rel is BOOK_LINK_REL on every anchor.
 
 export default function ScanPage() {
   const router = useRouter();
@@ -775,18 +769,22 @@ export default function ScanPage() {
 
           {/* Sportsbook hand-off (preserved feature) */}
           <div style={{ display: 'flex', flexWrap: 'wrap', gap: 8, justifyContent: 'center' }}>
-            {SPORTSBOOKS.map((b) => (
-              <a
-                key={b.id}
-                href={deepLink(b.host, selectedPlayer)}
-                target="_blank"
-                rel="noopener noreferrer"
-                className="mono"
-                style={{ padding: '7px 13px', fontSize: 11, fontWeight: 700, borderRadius: 6, border: '1px solid var(--border-hi)', color: 'var(--text-1)', textDecoration: 'none' }}
-              >
-                {b.label} ↗
-              </a>
-            ))}
+            {SUPPORTED_BOOKS.map((b) => {
+              const link = buildBookLink({ book: b.id, player: selectedPlayer, sport });
+              if (!link) return null;
+              return (
+                <a
+                  key={b.id}
+                  href={link.url}
+                  target="_blank"
+                  rel={BOOK_LINK_REL}
+                  className="mono"
+                  style={{ padding: '7px 13px', fontSize: 11, fontWeight: 700, borderRadius: 6, border: '1px solid var(--border-hi)', color: 'var(--text-1)', textDecoration: 'none' }}
+                >
+                  {b.label} ↗
+                </a>
+              );
+            })}
           </div>
 
           {/* Free-tier nudge — full paywall treatment returns in Phase G */}
diff --git a/web/src/components/PropRow.tsx b/web/src/components/PropRow.tsx
index 4395cf5..67f28e9 100644
--- a/web/src/components/PropRow.tsx
+++ b/web/src/components/PropRow.tsx
@@ -25,6 +25,10 @@ export interface PropRowProp {
   line: number;
   direction: PropDirection;
   book?: string;
+  // A1 S3 — the FULL per-book rows for this player+stat (the grouped
+  // odds shape from Express). Feeds best-price detection downstream;
+  // optional so legacy flat callers stay valid.
+  books?: Array<{ book?: string; line?: number; over_odds?: number | null; under_odds?: number | null }>;
   // Stable key used by the parent to look up grade results.
   key?: string;
 }
diff --git a/web/src/components/Slate.tsx b/web/src/components/Slate.tsx
index 18913ac..dafd884 100644
--- a/web/src/components/Slate.tsx
+++ b/web/src/components/Slate.tsx
@@ -345,6 +345,9 @@ function groupByGame(rawProps: RawProp[], sport: SlateSport): SlateGame[] {
       line: lineInfo.line,
       direction: lineInfo.direction,
       book: lineInfo.book,
+      // A1 S3 — keep the full per-book rows so the strip layer can mark
+      // the best available price (pickLine alone discards the comparison).
+      books: Array.isArray(r.lines) ? r.lines : undefined,
     });
   }
   // Sort each game's props by player + stat for stable rendering.
diff --git a/web/src/components/vyndr/PartnerRefCapture.tsx b/web/src/components/vyndr/PartnerRefCapture.tsx
new file mode 100644
index 0000000..0bcfe11
--- /dev/null
+++ b/web/src/components/vyndr/PartnerRefCapture.tsx
@@ -0,0 +1,16 @@
+'use client';
+
+import { useEffect } from 'react';
+import { captureRef } from '@/lib/partnerRef';
+
+/**
+ * PartnerRefCapture (A1 S3) — mounted once in the layout (GlobalHosts
+ * pattern). On first visit with ?ref=CODE it sets the first-party
+ * `vyndr_ref` cookie (90 days, first-touch). Renders nothing.
+ */
+export default function PartnerRefCapture() {
+  useEffect(() => {
+    captureRef(window);
+  }, []);
+  return null;
+}
diff --git a/web/src/components/vyndr/StatStrip.tsx b/web/src/components/vyndr/StatStrip.tsx
index 4138475..c0d3336 100644
--- a/web/src/components/vyndr/StatStrip.tsx
+++ b/web/src/components/vyndr/StatStrip.tsx
@@ -1,6 +1,10 @@
 import ArchetypeBadge from '@/components/vyndr/ArchetypeBadge';
 import GradeBadge from '@/components/vyndr/GradeBadge';
 import { nextRunLabelET } from '@/lib/pipelineSchedule';
+// A1 S3 — BOOK IT is a real per-book deep link now (organic until the
+// affiliate config flips a book on). rel MUST stay BOOK_LINK_REL.
+import { buildBookLink, BOOK_LINK_REL } from '@/lib/bookLinks';
+import { bookInfo } from '@/lib/books';
 
 export interface StatCell {
   label: string;
@@ -20,6 +24,10 @@ export interface StripProp {
   // Session 60 (Phase 2.5) — intraday movement + public revision.
   movement?: { kind: 'steam' | 'value' | 'against' | 'revised' | string; delta: number; currentLine: number } | null;
   revisedFrom?: string | null;
+  // A1 S3 — the prop's source book + the best available price across books
+  // (only set when ≥2 books post the same line and prices differ).
+  book?: string | null;
+  bestBook?: { book: string; odds: number } | null;
 }
 
 /** Phase 2.5 movement chip: STEAM ▲ (market chasing), VALUE ▲ (better
@@ -75,6 +83,7 @@ const Sep = ({ ch = '|' }: { ch?: string }) => (
 export default function StatStrip({
   player,
   team,
+  sport,
   archetype,
   stats,
   last10,
@@ -125,17 +134,45 @@ export default function StatStrip({
       </span>
     );
   };
-  // Session 52 — Push-to-Book teaser on graded props (feature not live yet).
+  // A1 S3 — BOOK IT is a real sportsbook deep link (was the Session 52
+  // teaser). Targets the best-priced book when one is known, else the
+  // prop's source book, else DraftKings. Links are ORGANIC until the
+  // operator flips a book in affiliateConfig — the anchor is identical
+  // either way, and rel is always BOOK_LINK_REL (sponsored noopener
+  // noreferrer) for affiliate compliance.
   const BookItTeaser = ({ p }: { p: StripProp }) => {
     if (!p.grade) return null;
+    const target = (p.bestBook && p.bestBook.book) || p.book || 'draftkings';
+    const link = buildBookLink({ book: target, player, sport });
+    if (!link) return null;
     return (
-      <span
+      <a
         className="mono"
-        title="Push-to-Book coming soon — connect your sportsbook"
-        style={{ fontSize: 9, fontWeight: 700, letterSpacing: '0.06em', color: 'var(--text-2)', cursor: 'default', padding: '2px 5px', borderRadius: 4, border: '1px solid var(--border)', opacity: 0.6 }}
+        href={link.url}
+        target="_blank"
+        rel={BOOK_LINK_REL}
+        onClick={(e) => e.stopPropagation()}
+        title={`Open ${bookInfo(target).name} — search lands on ${player}`}
+        style={{ fontSize: 9, fontWeight: 700, letterSpacing: '0.06em', color: 'var(--text-1)', cursor: 'pointer', padding: '2px 5px', borderRadius: 4, border: '1px solid var(--border)', textDecoration: 'none' }}
       >
         BOOK IT ⟶
-      </span>
+      </a>
+    );
+  };
+  // A1 S3 — best available price marker. ONE meaning: this prop's line is
+  // posted at a better price at `bestBook` than at least one other book.
+  // Renders only when the adapter verified ≥2 books at the same line.
+  const BestPriceDot = ({ p }: { p: StripProp }) => {
+    if (!p.bestBook) return null;
+    const odds = p.bestBook.odds;
+    const oddsStr = typeof odds === 'number' && odds > 0 ? `+${odds}` : String(odds);
+    return (
+      <span
+        title={`Best available price · ${bookInfo(p.bestBook.book).name} ${oddsStr}`}
+        aria-label={`Best available price at ${bookInfo(p.bestBook.book).name}, ${oddsStr}`}
+        style={{ width: 6, height: 6, borderRadius: '50%', display: 'inline-block', flexShrink: 0,
+          background: 'var(--g-a)', boxShadow: '0 0 0 2px rgba(0,212,160,.22)' }}
+      />
     );
   };
   const last10Str = typeof last10 === 'string'
@@ -226,7 +263,7 @@ export default function StatStrip({
                 <span key={i} style={{ display: 'inline-flex', alignItems: 'center', gap: 10 }}>
                   {i > 0 && <span style={{ color: '#3A3A48' }}>·</span>}
                   <span className="mono" style={{ display: 'inline-flex', alignItems: 'center', gap: 6, fontSize: 11, color: '#B8BCC8' }}>
-                    {p.stat} {p.side}{p.line} {p.grade && <GradeBadge grade={p.grade} size="sm" />}
+                    {p.stat} {p.side}{p.line} <BestPriceDot p={p} /> {p.grade && <GradeBadge grade={p.grade} size="sm" />}
                     <ParlayBtn p={p} />
                     <BookItTeaser p={p} />
                   </span>
@@ -245,6 +282,7 @@ export default function StatStrip({
                 return (
                   <div key={i} className="mono" style={{ fontSize: 11, color: 'var(--text-2)', display: 'flex', alignItems: 'center', gap: 8 }}>
                     <span style={{ color: 'var(--text-1)' }}>{p.stat} {p.line}</span>
+                    <BestPriceDot p={p} />
                     <span style={{ color: 'var(--text-2)', fontStyle: 'italic' }}>{next ? `Grades post ${next}` : 'Awaiting next scan'}</span>
                   </div>
                 );
@@ -254,6 +292,7 @@ export default function StatStrip({
                 <div key={i} style={{ display: 'flex', flexDirection: 'column', gap: 2 }}>
                   <div className="mono" style={{ display: 'inline-flex', alignItems: 'center', gap: 7, fontSize: 12, color: '#B8BCC8' }}>
                     <span style={{ color: '#fff' }}>{p.stat} {p.side}{p.line}</span>
+                    <BestPriceDot p={p} />
                     {/* Phase 2.5 — a revised grade is PUBLIC: original struck through. */}
                     {p.revisedFrom && (
                       <span className="mono" title="Grade revised after the line moved against the read — original preserved" style={{ fontSize: 10.5, color: 'var(--text-2)', textDecoration: 'line-through' }}>{p.revisedFrom}</span>
diff --git a/web/src/contexts/AuthContext.tsx b/web/src/contexts/AuthContext.tsx
index 94b9d7e..344ea77 100644
--- a/web/src/contexts/AuthContext.tsx
+++ b/web/src/contexts/AuthContext.tsx
@@ -3,6 +3,7 @@
 import { createContext, useCallback, useContext, useEffect, useMemo, useState } from 'react';
 import type { Session, User } from '@supabase/supabase-js';
 import { getBrowserSupabase } from '@/lib/supabase';
+import { readRefCookie } from '@/lib/partnerRef';
 
 export type Tier = 'free' | 'analyst' | 'desk';
 
@@ -135,10 +136,17 @@ export default function AuthProvider({ children }: { children: React.ReactNode }
     async (email, password, ageVerified) => {
       if (!ageVerified) return { error: 'You must confirm you are 21 or older.' };
       if (!supabase) return { error: 'Auth is not configured. Set Supabase env vars.' };
+      // A1 S3 — partner attribution: forward the first-touch vyndr_ref
+      // cookie (set by PartnerRefCapture on a ?ref=CODE visit) into the
+      // signup metadata. The internal /api/partners report reads it.
+      const partnerRef = readRefCookie(document.cookie);
       const { error } = await supabase.auth.signUp({
         email,
         password,
-        options: { emailRedirectTo: `${window.location.origin}/auth/callback` },
+        options: {
+          emailRedirectTo: `${window.location.origin}/auth/callback`,
+          ...(partnerRef ? { data: { partner_ref: partnerRef } } : {}),
+        },
       });
       if (error) return { error: error.message };
       return {};
diff --git a/web/src/lib/affiliateConfig.js b/web/src/lib/affiliateConfig.js
new file mode 100644
index 0000000..4647e7c
--- /dev/null
+++ b/web/src/lib/affiliateConfig.js
@@ -0,0 +1,37 @@
+/* ============================================================
+   Affiliate configuration (A1 Session 3).
+
+   NO AFFILIATE PROGRAM IS APPROVED YET. Every book ships
+   `enabled: false` — bookLinks.js builds clean ORGANIC links until
+   an operator flips a book on and fills its params. This file is the
+   single flip point; no component hardcodes tracking params.
+
+   Param shapes by network (fill when approved — placeholders only):
+
+   Impact Radius (DraftKings, FanDuel run on Impact):
+     { irclickid: '<click-id template or static campaign id>',
+       sharedid: 'vyndr',            // sub-affiliate / source tag
+       wpsrc:    '<campaign source>' }
+
+   Partnerize / btag-style (BetMGM, Caesars, BetRivers):
+     { btag:  '<partner btag>',       // BetMGM/Caesars partner tag
+       afid:  '<affiliate id>',       // network affiliate id
+       siteid:'<site/property id>' }
+
+   Rules:
+   - `tracking: true` is only reported when a book is enabled AND at
+     least one non-empty param actually lands on the URL.
+   - Never invent values here — empty string params are skipped by the
+     builder, so a half-filled config still degrades to organic-plus-
+     whatever-is-real, never a fabricated id.
+   ============================================================ */
+
+const AFFILIATE_CONFIG = {
+  draftkings: { enabled: false, params: {} }, // Impact — irclickid / sharedid / wpsrc
+  fanduel: { enabled: false, params: {} }, // Impact — irclickid / sharedid / wpsrc
+  betmgm: { enabled: false, params: {} }, // Partnerize — btag / afid / siteid
+  caesars: { enabled: false, params: {} }, // Partnerize — btag / afid / siteid
+  betrivers: { enabled: false, params: {} }, // btag / afid / siteid
+};
+
+module.exports = { AFFILIATE_CONFIG };
diff --git a/web/src/lib/bookLinks.js b/web/src/lib/bookLinks.js
new file mode 100644
index 0000000..9dba460
--- /dev/null
+++ b/web/src/lib/bookLinks.js
@@ -0,0 +1,95 @@
+/* ============================================================
+   BOOK IT deep-link builder (A1 Session 3).
+
+   Builds a per-book player-prop hand-off URL:
+     buildBookLink({ book, player, sport, state? }) → { url, tracking } | null
+
+   - Base hosts mirror the scan page's legacy SPORTSBOOKS list; the
+     organic URL shape (`/?search=<player>`) is the shape the product
+     has always shipped.
+   - The affiliate layer reads web/src/lib/affiliateConfig.js. Every
+     book is `enabled: false` today (no program approved), so links are
+     clean + organic. Flipping a book's config produces a tracked URL —
+     no component changes needed.
+   - Every rendered book anchor must carry BOOK_LINK_REL
+     ("sponsored noopener noreferrer") — sponsored is required for
+     affiliate compliance and harmless on organic links.
+   - Unknown book → null. Absent beats wrong.
+
+   CommonJS so the plain-JS Jest suite requires it AND .tsx imports it
+   (allowJs) — same pattern as slateAdapter/books/playerName.
+   ============================================================ */
+
+const { bookKey } = require('./books');
+const { AFFILIATE_CONFIG } = require('./affiliateConfig');
+
+/** rel attribute every sportsbook anchor must render. */
+const BOOK_LINK_REL = 'sponsored noopener noreferrer';
+
+/** The books we build deep links for (order = display order). */
+const SUPPORTED_BOOKS = [
+  { id: 'draftkings', label: 'DraftKings', host: 'sportsbook.draftkings.com' },
+  { id: 'fanduel', label: 'FanDuel', host: 'sportsbook.fanduel.com' },
+  { id: 'betmgm', label: 'BetMGM', host: 'sports.betmgm.com' },
+  { id: 'caesars', label: 'Caesars', host: 'sportsbook.caesars.com' },
+  // BetRivers routes by state subdomain (mi.betrivers.com); www works
+  // as the state-agnostic landing.
+  { id: 'betrivers', label: 'BetRivers', host: 'www.betrivers.com' },
+];
+
+const HOSTS = SUPPORTED_BOOKS.reduce((m, b) => {
+  m[b.id] = b.host;
+  return m;
+}, {});
+
+/** Canonicalize any book spelling ("DK", "DraftKings", "draftkings") →
+ *  a SUPPORTED_BOOKS id, or null when it isn't a book we link to. */
+function resolveBookId(book) {
+  const k = bookKey(book);
+  return HOSTS[k] ? k : null;
+}
+
+/** Two-letter US state code or null — anything else is dropped, never guessed. */
+function cleanState(state) {
+  const s = String(state == null ? '' : state).trim().toLowerCase();
+  return /^[a-z]{2}$/.test(s) ? s : null;
+}
+
+/**
+ * Build the deep link for one book + player.
+ *
+ * @param {{ book: string, player: string, sport?: string, state?: string }} input
+ * @param {object} [config] — injectable for tests; defaults to AFFILIATE_CONFIG.
+ * @returns {{ url: string, tracking: boolean } | null}
+ */
+function buildBookLink(input, config = AFFILIATE_CONFIG) {
+  const { book, player, state } = input || {};
+  const id = resolveBookId(book);
+  if (!id || !player) return null;
+
+  let host = HOSTS[id];
+  if (id === 'betrivers') {
+    const st = cleanState(state);
+    if (st) host = `${st}.betrivers.com`;
+  }
+
+  const url = new URL(`https://${host}/`);
+  url.searchParams.set('search', String(player));
+
+  // Affiliate layer — only when the operator flipped this book on AND
+  // real (non-empty) params exist. Otherwise the link stays organic.
+  let tracking = false;
+  const cfg = config && config[id];
+  if (cfg && cfg.enabled === true && cfg.params && typeof cfg.params === 'object') {
+    for (const [key, value] of Object.entries(cfg.params)) {
+      const v = String(value == null ? '' : value).trim();
+      if (!key || !v) continue; // never emit an empty/fabricated id
+      url.searchParams.set(key, v);
+      tracking = true;
+    }
+  }
+
+  return { url: url.toString(), tracking };
+}
+
+module.exports = { buildBookLink, resolveBookId, SUPPORTED_BOOKS, BOOK_LINK_REL };
diff --git a/web/src/lib/partnerRef.js b/web/src/lib/partnerRef.js
new file mode 100644
index 0000000..bdd9d23
--- /dev/null
+++ b/web/src/lib/partnerRef.js
@@ -0,0 +1,83 @@
+/* ============================================================
+   Partner ref capture (A1 Session 3).
+
+   A partner shares vyndr.app/?ref=CODE. On first visit we set a
+   FIRST-PARTY cookie `vyndr_ref` (90 days). Signup forwards the code
+   into Supabase user metadata as `partner_ref`, which is what the
+   internal /api/partners/report/:code attribution reads.
+
+   Attribution model = FIRST TOUCH: an existing vyndr_ref cookie is
+   never overwritten by a later ?ref= visit. Codes are sanitized
+   (A-Z 0-9 - _, max 32) and stored UPPERCASE — the same convention
+   as Stripe promo codes (see docs/PARTNERS.md).
+
+   CommonJS so the plain-JS Jest suite exercises it directly.
+   ============================================================ */
+
+const REF_COOKIE = 'vyndr_ref';
+const REF_TTL_DAYS = 90;
+
+/** Sanitize a raw code → canonical UPPERCASE code, or null. */
+function sanitizeRefCode(raw) {
+  const s = String(raw == null ? '' : raw).trim().toUpperCase();
+  if (!s || s.length > 32) return null;
+  return /^[A-Z0-9_-]+$/.test(s) ? s : null;
+}
+
+/** Pull a sanitized ?ref= code out of a location.search string. */
+function parseRefFromSearch(search) {
+  try {
+    const params = new URLSearchParams(search || '');
+    return sanitizeRefCode(params.get('ref'));
+  } catch {
+    return null;
+  }
+}
+
+/** Read the vyndr_ref value out of a document.cookie string. */
+function readRefCookie(cookieStr) {
+  const parts = String(cookieStr == null ? '' : cookieStr).split(';');
+  for (const part of parts) {
+    const [name, ...rest] = part.split('=');
+    if (name && name.trim() === REF_COOKIE) {
+      return sanitizeRefCode(decodeURIComponent(rest.join('=').trim()));
+    }
+  }
+  return null;
+}
+
+/** Build the Set-Cookie string for a code (first-party, 90d, lax). */
+function buildRefCookie(code, { days = REF_TTL_DAYS, secure = false } = {}) {
+  const clean = sanitizeRefCode(code);
+  if (!clean) return null;
+  const maxAge = Math.round(days * 24 * 60 * 60);
+  return `${REF_COOKIE}=${encodeURIComponent(clean)}; Max-Age=${maxAge}; Path=/; SameSite=Lax${secure ? '; Secure' : ''}`;
+}
+
+/**
+ * Capture ?ref=CODE from the current visit into the cookie.
+ * First-touch: no-op when the cookie already exists. `win` is
+ * injectable for tests (defaults to the browser window).
+ * Returns the code that was captured, or null.
+ */
+function captureRef(win) {
+  const w = win || (typeof window !== 'undefined' ? window : null);
+  if (!w || !w.document || !w.location) return null;
+  const code = parseRefFromSearch(w.location.search);
+  if (!code) return null;
+  if (readRefCookie(w.document.cookie)) return null; // first touch wins
+  const cookie = buildRefCookie(code, { secure: w.location.protocol === 'https:' });
+  if (!cookie) return null;
+  w.document.cookie = cookie;
+  return code;
+}
+
+module.exports = {
+  REF_COOKIE,
+  REF_TTL_DAYS,
+  sanitizeRefCode,
+  parseRefFromSearch,
+  readRefCookie,
+  buildRefCookie,
+  captureRef,
+};
diff --git a/web/src/lib/slateAdapter.js b/web/src/lib/slateAdapter.js
index e4c08ba..0bc7e2d 100644
--- a/web/src/lib/slateAdapter.js
+++ b/web/src/lib/slateAdapter.js
@@ -51,6 +51,49 @@ function detectBestLines(books) {
   }));
 }
 
+/**
+ * Best available price across a prop's book rows (A1 Session 3).
+ *
+ * `rows` is the grouped odds shape the Express /api/odds proxy already
+ * ships the browser: [{ book, line, over_odds, under_odds }] — one row
+ * per book for the same player+stat.
+ *
+ * Data-semantics rule: a "best price" claim is only honest when ≥2 books
+ * post the SAME line for the side and their prices differ — comparing
+ * odds across different lines is meaningless, and a lone price isn't
+ * "best". Anything else → null. Absent beats wrong.
+ *
+ * @param {Array<{book?:string,line?:number,over_odds?:number|null,under_odds?:number|null}>} rows
+ * @param {string} [side] — 'over' | 'under' (default over)
+ * @param {number|null} [refLine] — the line the card displays; when given,
+ *   only books at that exact line compete.
+ * @returns {{ book: string, odds: number } | null}
+ */
+function detectBestBook(rows, side = 'over', refLine = null) {
+  const key = String(side || 'over').toLowerCase().startsWith('u') ? 'under_odds' : 'over_odds';
+  const valid = (Array.isArray(rows) ? rows : []).filter(
+    (r) => r && r.book && Number.isFinite(r.line) && r[key] != null && parseAmericanOdds(r[key]) != null,
+  );
+  if (valid.length < 2) return null;
+
+  // Compare at ONE line: the displayed line when given, else the modal line.
+  let line = Number.isFinite(refLine) ? refLine : null;
+  if (line == null) {
+    const counts = new Map();
+    for (const r of valid) counts.set(r.line, (counts.get(r.line) || 0) + 1);
+    let bestCount = 0;
+    for (const [ln, c] of counts) if (c > bestCount) { bestCount = c; line = ln; }
+  }
+  const atLine = valid.filter((r) => r.line === line);
+  if (atLine.length < 2) return null;
+
+  const decimals = atLine.map((r) => parseAmericanOdds(r[key]));
+  const max = Math.max(...decimals);
+  if (max === Math.min(...decimals)) return null; // identical prices → no "best"
+  const winner = atLine[decimals.indexOf(max)];
+  return { book: winner.book, odds: winner[key] };
+}
+
 function formatGameTime(iso) {
   if (!iso) return '';
   try {
@@ -309,6 +352,11 @@ function buildPlayerStripsFromProps(gameProps, gradeIndex, deltaIndex, now = Dat
         line: rec.line,
         side,
         grade: rec.grade,
+        // A1 S3 — the prop's own book + the best available price across the
+        // game's book rows for the graded side (null unless ≥2 books at the
+        // same current line disagree — see detectBestBook).
+        book: p.book || null,
+        bestBook: detectBestBook(p.books, side === 'U' ? 'under' : 'over', p.line),
         gradedAt: rec.gradedAt
           ? { ...rec.gradedAt, ago: gradedAgo(rec.gradedAt.timestamp, now) }
           : null,
@@ -324,6 +372,8 @@ function buildPlayerStripsFromProps(gameProps, gradeIndex, deltaIndex, now = Dat
     } else {
       byPlayer[pk].props.push({
         stat: statShort(p.stat_type || p.stat), line: p.line, side: '', grade: null, awaiting: true,
+        book: p.book || null,
+        bestBook: detectBestBook(p.books, p.direction || 'over', p.line),
       });
     }
   }
@@ -374,6 +424,7 @@ function pitchersForGameTeams(awayTeam, homeTeam, pitcherMap) {
 module.exports = {
   parseAmericanOdds,
   detectBestLines,
+  detectBestBook,
   mapGameLines,
   mapScheduleToGameCards,
   formatGameTime,