Merge pull request 'claude/llws-double-elimination-bracket-oaj093' (#138) from claude/llws-double-elimination-bracket-oaj093 into main

Reviewed-on: #138

app/components/scoring/PlayoffBracket.tsx

@@ -196,16 +196,50 @@ export interface ConsolationRound {
 
 /**
  * Find the template's consolation round, if it has one.
+ *
+ * A consolation round must be TERMINAL — its winner plays no further game, which is
+ * what lets its result split two exact positions. `loserFeedsInto` alone is not
+ * enough: a double-elimination bracket (llws_20) uses it on every winners-bracket
+ * round to route losers into the elimination bracket, and those targets are ordinary
+ * rounds that feed onward. Picking the first `loserFeedsInto` there would mistake
+ * "Elimination Round 1" for a third-place game and corrupt the final rankings.
+ *
  * Exported for unit testing.
  */
 export function findConsolationRound(
   template: BracketTemplate | undefined
 ): ConsolationRound | undefined {
-  const feeder = template?.rounds.find((r) => r.loserFeedsInto);
+  const isTerminal = (roundName: string) =>
+    template?.rounds.find((r) => r.name === roundName)?.feedsInto === null;
+
+  const feeder = template?.rounds.find(
+    (r) => r.loserFeedsInto && isTerminal(r.loserFeedsInto)
+  );
   if (!feeder?.loserFeedsInto) return undefined;
   return { round: feeder.loserFeedsInto, feederRound: feeder.name };
 }
 
+/**
+ * Round names whose losers are placed by some LATER round rather than finishing where
+ * they lost — i.e. double-elimination winners-bracket rounds, whose losers drop into
+ * the elimination bracket.
+ *
+ * The consolation feeder is deliberately excluded: its losers do finish at that tier
+ * (the consolation game splits their two positions), so it still consumes them.
+ *
+ * Exported for unit testing.
+ */
+export function roundsWithLosersPlacedLater(
+  template: BracketTemplate | undefined,
+  consolation: ConsolationRound | undefined
+): Set<string> {
+  return new Set(
+    (template?.rounds ?? [])
+      .filter((r) => r.loserFeedsInto && r.name !== consolation?.feederRound)
+      .map((r) => r.name)
+  );
+}
+
 /**
  * Build the ordered final-rankings list from completed matches.
  *
@@ -228,7 +262,9 @@ export function computeRankedEntries(
   rounds: string[],
   matchesByRound: Map<string, Match[]>,
   consolation: ConsolationRound | undefined,
-  ownershipMap: Map<string, TeamOwnership>
+  ownershipMap: Map<string, TeamOwnership>,
+  /** See roundsWithLosersPlacedLater. Empty for single-elimination brackets. */
+  losersPlacedLater: Set<string> = new Set()
 ): EliminatedEntry[] {
   const eliminatedByRound = computeEliminatedByRound(matches, rounds);
 
@@ -300,6 +336,14 @@ export function computeRankedEntries(
     // consumes none of its own.
     if (consolationActive && roundName === consolation?.round) continue;
 
+    // A round normally consumes one position per match — its losers finish here,
+    // whether or not the games have been played yet (four semifinalists occupy 1–4
+    // regardless). But in a double-elimination bracket a winners-bracket loss places
+    // nobody: the loser drops into the elimination bracket and is ranked by whatever
+    // knocks them out later. Those rounds must consume nothing, or every position
+    // below inflates (a 20-team llws_20 bracket would end at "T23").
+    if (losersPlacedLater.has(roundName)) continue;
+
     nextRank += matchesByRound.get(roundName)?.length ?? 0;
   }
 
@@ -371,7 +415,8 @@ export function PlayoffBracket({
     rounds,
     matchesByRound,
     consolation,
-    ownershipMap
+    ownershipMap,
+    roundsWithLosersPlacedLater(template, consolation)
   );
 
   const rankedParticipantIds = new Set(rankedEntries.map((e) => e.participant.id));

app/components/scoring/TabbedBracketLayout.tsx

@@ -152,7 +152,22 @@ export function TabbedBracketLayout({
         const simpleRounds = phase.groups ? [] : (phase.rounds ?? []).filter((r) => rounds.includes(r));
 
         const phaseRounds = phase.groups ? [...groupRounds, ...sharedRounds] : simpleRounds;
-        const phaseMatchesByRound = new Map(phaseRounds.map((r) => [r, matchesByRound.get(r) ?? []]));
+        // Restrict each round to the match numbers this phase's groups actually claim.
+        // Rounds can be shared across phases (LLWS runs U.S. and International through
+        // the same rounds), so without this the mobile view would merge both sides into
+        // one column. No-op where a phase's groups already cover every match in the
+        // round (NCAA regions, NBA conferences) and for sharedRounds, which have no
+        // group filter.
+        const phaseMatchesByRound = new Map(
+          phaseRounds.map((r) => {
+            const all = matchesByRound.get(r) ?? [];
+            if (!phase.groups || sharedRounds.includes(r)) return [r, all] as const;
+            const allowed = new Set(
+              phase.groups.flatMap((g) => g.roundMatchNumbers[r] ?? [])
+            );
+            return [r, allowed.size > 0 ? all.filter((m) => allowed.has(m.matchNumber)) : all] as const;
+          })
+        );
         const sharedMatchesByRound = new Map(sharedRounds.map((r) => [r, matchesByRound.get(r) ?? []]));
 
         const phaseFirstScoringIdx = phaseRounds.findIndex((r) => rounds.indexOf(r) >= scoringRoundIdx);

app/components/scoring/__tests__/PlayoffBracket.test.tsx

@@ -7,9 +7,11 @@ import {
   computeEliminatedByRound,
   computeRankedEntries,
   findConsolationRound,
+  roundsWithLosersPlacedLater,
   type Match,
 } from "../PlayoffBracket";
 import { getBracketTemplate } from "~/lib/bracket-templates";
+import { resolveLLWSAdvancement } from "~/models/playoff-match";
 
 // ---------------------------------------------------------------------------
 // Helpers
@@ -426,6 +428,129 @@ function rankOf(entries: ReturnType<typeof computeRankedEntries>, id: string) {
   return entries.find((e) => e.participant.id === id)?.rankLabel;
 }
 
+// ---------------------------------------------------------------------------
+// llws_20 — double elimination, where a winners-bracket loss places nobody
+// ---------------------------------------------------------------------------
+
+/** Stable participant id for an llws_20 bracket slot. */
+function llwsTeam(i: number): string {
+  return `t${String(i).padStart(2, "0")}`;
+}
+
+/**
+ * Play a full 20-team LLWS tournament, always advancing the lower-numbered
+ * participant id so the outcome is deterministic, and return every match.
+ * Routing comes from the real advancement map rather than being hand-listed.
+ */
+function llwsMatches(): Match[] {
+  const template = getBracketTemplate("llws_20");
+  if (!template) throw new Error("llws_20 template missing");
+
+  // round → matchNumber → [p1, p2]
+  const slots = new Map<string, Map<number, [string | null, string | null]>>();
+  for (const round of template.rounds) {
+    const byNumber = new Map<number, [string | null, string | null]>();
+    for (let n = 1; n <= round.matchCount; n++) byNumber.set(n, [null, null]);
+    slots.set(round.name, byNumber);
+  }
+  const put = (round: string, n: number, slot: 0 | 1, id: string) => {
+    const pair = slots.get(round)?.get(n);
+    if (pair) pair[slot] = id;
+  };
+
+  // Seed the Opening Round and the four byes, mirroring generateLLWS20Bracket.
+  for (const [base, roundBase] of [[0, 1], [10, 5]] as const) {
+    for (let local = 0; local < 4; local++) {
+      put("Opening Round", roundBase + local, 0, llwsTeam(base + local * 2));
+      put("Opening Round", roundBase + local, 1, llwsTeam(base + local * 2 + 1));
+    }
+  }
+  put("Winners Round 2", 1, 0, llwsTeam(8));
+  put("Winners Round 2", 2, 0, llwsTeam(9));
+  put("Winners Round 2", 3, 0, llwsTeam(18));
+  put("Winners Round 2", 4, 0, llwsTeam(19));
+
+  const matches: Match[] = [];
+  for (const round of template.rounds) {
+    for (let n = 1; n <= round.matchCount; n++) {
+      const [p1, p2] = slots.get(round.name)?.get(n) ?? [null, null];
+      if (!p1 || !p2) throw new Error(`${round.name} #${n} was not filled`);
+      // Deterministic: the lower id always wins.
+      const winnerId = p1 < p2 ? p1 : p2;
+      const loserId = p1 < p2 ? p2 : p1;
+      matches.push(
+        makeRankedMatch(round.name, n, winnerId, loserId, {
+          winnerSlot: winnerId === p1 ? 1 : 2,
+        })
+      );
+      const { winner, loser } = resolveLLWSAdvancement(round.name, n);
+      if (winner) put(winner.round, winner.matchNumber, winner.slot === "participant1Id" ? 0 : 1, winnerId);
+      if (loser) put(loser.round, loser.matchNumber, loser.slot === "participant1Id" ? 0 : 1, loserId);
+    }
+  }
+  return matches;
+}
+
+describe("computeRankedEntries — llws_20 double elimination", () => {
+  const template = getBracketTemplate("llws_20");
+  const rounds = template?.rounds.map((r) => r.name) ?? [];
+
+  function rankLlws() {
+    const matches = llwsMatches();
+    const consolation = findConsolationRound(template);
+    return computeRankedEntries(
+      matches,
+      rounds,
+      groupMatchesByRound(matches),
+      consolation,
+      new Map(),
+      roundsWithLosersPlacedLater(template, consolation)
+    );
+  }
+
+  it("ranks all 19 non-champions exactly once", () => {
+    const entries = rankLlws();
+    expect(entries).toHaveLength(19);
+    expect(new Set(entries.map((e) => e.participant.id)).size).toBe(19);
+  });
+
+  it("gives the top 8 the positions the scoring tiers depend on", () => {
+    const entries = rankLlws();
+    const labels = entries.map((e) => e.rankLabel);
+    // 2nd (World Championship loser), then 3rd and 4th decided by the consolation
+    // game, then the two 5–6 and two 7–8 tier teams.
+    expect(labels[0]).toBe("T2");
+    expect(labels.filter((l) => l === "3")).toHaveLength(1);
+    expect(labels.filter((l) => l === "4")).toHaveLength(1);
+    expect(labels.filter((l) => l === "T5")).toHaveLength(2);
+    expect(labels.filter((l) => l === "T7")).toHaveLength(2);
+  });
+
+  it("does not inflate positions below the top 8", () => {
+    // Winners-bracket losses place nobody — those teams are ranked by the
+    // elimination-bracket game that actually knocks them out. If the winners
+    // rounds consumed positions, the last tier would read T23 in a 20-team field.
+    const entries = rankLlws();
+    const labels = entries.map((e) => e.rankLabel);
+    expect(labels.filter((l) => l === "T9")).toHaveLength(4);
+    expect(labels.filter((l) => l === "T13")).toHaveLength(4);
+    expect(labels.filter((l) => l === "T17")).toHaveLength(4);
+    // 1 champion (not in the list) + 19 ranked = the full 20-team field.
+    expect(labels.some((l) => Number(l.replace("T", "")) > 17)).toBe(false);
+  });
+
+  it("never ranks a winners-bracket loser at the round they first lost", () => {
+    const entries = rankLlws();
+    // t00 wins every game it plays (lowest id), so take a team that loses in the
+    // winners bracket but survives: the Opening Round M1 loser, t01.
+    const t01 = entries.find((e) => e.participant.id === "t01");
+    expect(t01).toBeDefined();
+    // Losing the opening game must not park them in the bottom tier — they got a
+    // second life in the elimination bracket.
+    expect(t01?.rankLabel).not.toBe("T17");
+  });
+});
+
 describe("findConsolationRound", () => {
   it("identifies the fifa_48 third place game and the round that feeds it", () => {
     expect(findConsolationRound(getBracketTemplate("fifa_48"))).toEqual({
@@ -441,6 +566,17 @@ describe("findConsolationRound", () => {
   it("returns undefined when there is no template", () => {
     expect(findConsolationRound(undefined)).toBeUndefined();
   });
+
+  it("ignores double-elimination loser routing and finds the real consolation game", () => {
+    // llws_20 sets loserFeedsInto on every winners-bracket round to route losers
+    // into the elimination bracket. Only the Bracket Championship feeds a terminal
+    // round; taking the first loserFeedsInto instead would mistake "Elimination
+    // Round 1" for a third-place game and corrupt the final rankings.
+    expect(findConsolationRound(getBracketTemplate("llws_20"))).toEqual({
+      round: "Consolation Third Place",
+      feederRound: "Bracket Championship",
+    });
+  });
 });
 
 describe("computeRankedEntries", () => {

app/lib/bracket-templates.ts

@@ -19,6 +19,18 @@ export interface BracketRound {
    * When set, the loser of each match in this round is placed into the target round.
    */
   loserFeedsInto?: string | null;
+  /**
+   * Floor position banked by the WINNER of a *non-scoring* round.
+   *
+   * Omit for the default behavior: winners entering the first scoring round bank a
+   * T5–T8 floor (position 5), everyone else banks nothing. Set an explicit number when
+   * that default is wrong — in a double-elimination losers bracket a win can guarantee
+   * a worse finish than 5th (llws_20 "Elimination Round 3" → 7). Set null to bank no
+   * floor even though the next round scores.
+   *
+   * Has no effect on scoring rounds, which use RoundScoringConfig.winnerFloor instead.
+   */
+  nonScoringWinnerFloor?: number | null;
 }
 
 export interface GroupStageConfig {
@@ -934,6 +946,258 @@ export const NBA_20: BracketTemplate = {
   ],
 };
 
+// ── LLWS 20 ───────────────────────────────────────────────────────────────────
+
+/** Side-local match numbers → global match numbers, per round shape. */
+const LLWS_OPENING_OFFSET = 4;   // Opening Round: US M1–4, Intl M5–8
+const LLWS_PAIR_OFFSET = 2;      // 4-match rounds: US M1–2, Intl M3–4
+const LLWS_SOLO_OFFSET = 1;      // 2-match rounds: US M1, Intl M2
+
+/** Rounds with 4 matches (2 per side). Opening Round has 8; the rest have 2. */
+export const LLWS_FOUR_MATCH_ROUNDS = new Set([
+  "Winners Round 2",
+  "Elimination Round 1",
+  "Winners Semifinals",
+  "Elimination Round 2",
+  "Elimination Round 3",
+]);
+
+/**
+ * Returns the global match number for a side-local match in an LLWS round.
+ * side 0 = United States, side 1 = International.
+ */
+export function llwsMatchNumber(round: string, side: 0 | 1, localMatch: number): number {
+  const offset =
+    round === "Opening Round"
+      ? LLWS_OPENING_OFFSET
+      : LLWS_FOUR_MATCH_ROUNDS.has(round)
+        ? LLWS_PAIR_OFFSET
+        : LLWS_SOLO_OFFSET;
+  return localMatch + side * offset;
+}
+
+/**
+ * Inverse of llwsMatchNumber: global match number → { side, localMatch }.
+ */
+export function llwsSideAndLocal(
+  round: string,
+  matchNumber: number
+): { side: 0 | 1; localMatch: number } {
+  const offset =
+    round === "Opening Round"
+      ? LLWS_OPENING_OFFSET
+      : LLWS_FOUR_MATCH_ROUNDS.has(round)
+        ? LLWS_PAIR_OFFSET
+        : LLWS_SOLO_OFFSET;
+  const side: 0 | 1 = matchNumber > offset ? 1 : 0;
+  return { side, localMatch: matchNumber - side * offset };
+}
+
+/**
+ * Little League Baseball World Series (20 teams, 2025+ double-elimination format)
+ *
+ * Two independent 10-team double-elimination brackets — United States and
+ * International — each producing a side champion, then a World Championship game and
+ * a Consolation Third Place game between the two side runners-up.
+ *
+ * Rounds are shared across both sides: U.S. matches take the low match numbers and
+ * International the high ones (see llwsMatchNumber). The phases/groups config splits
+ * them back apart for display.
+ *
+ * A loss in the winners bracket is NOT an elimination — it drops the team into the
+ * elimination bracket at a specific slot (see advanceLLWSWinner in models/playoff-match).
+ * A loss in the elimination bracket is final.
+ *
+ * There is deliberately NO "if necessary" game: the winners-bracket champion is out if
+ * it loses the Bracket Championship, dropping to the Consolation game rather than
+ * forcing a rematch. This is the official LLWS modified double-elimination format.
+ *
+ * Placement tiers (only 8 teams score — the field is exactly 8 when Elim R4 begins):
+ *   1st / 2nd  World Championship
+ *   3rd / 4th  Consolation Third Place (real game, so positions are distinct)
+ *   5th / 6th  Elimination Final losers
+ *   7th / 8th  Elimination Round 4 losers
+ *   0 pts      the 12 teams eliminated in Elimination Rounds 1–3
+ *
+ * Participant array layout (20 slots):
+ *   [0–7]   U.S. Opening Round teams, two per game (M1..M4)
+ *   [8, 9]  U.S. bye teams, entering Winners Round 2 M1 / M2 at participant1
+ *   [10–17] International Opening Round teams, two per game (M5..M8)
+ *   [18,19] International bye teams, entering Winners Round 2 M3 / M4 at participant1
+ */
+export const LLWS_20: BracketTemplate = {
+  id: "llws_20",
+  name: "Little League World Series (20 teams)",
+  totalTeams: 20,
+  scoringStartsAtRound: "Winners Final",
+  // Ordered by the real schedule so non-phased views read chronologically.
+  rounds: [
+    {
+      name: "Opening Round",
+      matchCount: 8,
+      feedsInto: "Winners Round 2",
+      isScoring: false,
+      loserFeedsInto: "Elimination Round 1",
+      nonScoringWinnerFloor: null, // 16 teams still alive — nothing guaranteed
+    },
+    {
+      name: "Winners Round 2",
+      matchCount: 4,
+      feedsInto: "Winners Semifinals",
+      isScoring: false,
+      loserFeedsInto: "Elimination Round 2",
+      nonScoringWinnerFloor: null,
+    },
+    {
+      name: "Elimination Round 1",
+      matchCount: 4,
+      feedsInto: "Elimination Round 2",
+      isScoring: false, // losers finish 13th–16th
+      nonScoringWinnerFloor: null,
+    },
+    {
+      name: "Winners Semifinals",
+      matchCount: 4,
+      feedsInto: "Winners Final",
+      isScoring: false,
+      loserFeedsInto: "Elimination Round 3",
+      // Reaching the Winners Final guarantees at worst 5th (lose it, then lose the
+      // Elimination Final). Same value as the engine default, stated explicitly.
+      nonScoringWinnerFloor: 5,
+    },
+    {
+      name: "Elimination Round 2",
+      matchCount: 4,
+      feedsInto: "Elimination Round 3",
+      isScoring: false, // losers finish 11th–12th
+      nonScoringWinnerFloor: null,
+    },
+    {
+      name: "Elimination Round 3",
+      matchCount: 4,
+      feedsInto: "Elimination Round 4",
+      isScoring: false, // losers finish 9th–10th
+      // Winners reach Elimination Round 4, where a loss is 7th — not 5th.
+      nonScoringWinnerFloor: 7,
+    },
+    {
+      name: "Winners Final",
+      matchCount: 2,
+      feedsInto: "Bracket Championship",
+      isScoring: true, // loser drops to the Elimination Final (provisional 5th)
+      loserFeedsInto: "Elimination Final",
+    },
+    {
+      name: "Elimination Round 4",
+      matchCount: 2,
+      feedsInto: "Elimination Final",
+      isScoring: true, // losers share 7th–8th
+    },
+    {
+      name: "Elimination Final",
+      matchCount: 2,
+      feedsInto: "Bracket Championship",
+      isScoring: true, // losers share 5th–6th
+    },
+    {
+      name: "Bracket Championship",
+      matchCount: 2,
+      feedsInto: "World Championship",
+      isScoring: true, // loser drops to the Consolation game (provisional 4th)
+      loserFeedsInto: "Consolation Third Place",
+    },
+    {
+      name: "Consolation Third Place",
+      matchCount: 1,
+      feedsInto: null,
+      isScoring: true, // winner 3rd, loser 4th
+    },
+    {
+      name: "World Championship",
+      matchCount: 1,
+      feedsInto: null,
+      isScoring: true, // winner 1st, loser 2nd
+    },
+  ],
+  // Region assignments rotate year to year (which region draws the bye changes), so
+  // these are positional slot labels rather than region names. Kept short — the admin
+  // form renders them in a narrow fixed-width column alongside each participant picker.
+  participantLabels: [
+    "US G1 Home", "US G1 Away",
+    "US G2 Home", "US G2 Away",
+    "US G3 Home", "US G3 Away",
+    "US G4 Home", "US G4 Away",
+    "US Bye 1", "US Bye 2",
+    "Intl G1 Home", "Intl G1 Away",
+    "Intl G2 Home", "Intl G2 Away",
+    "Intl G3 Home", "Intl G3 Away",
+    "Intl G4 Home", "Intl G4 Away",
+    "Intl Bye 1", "Intl Bye 2",
+  ],
+  phases: [
+    {
+      name: "United States",
+      groups: [
+        {
+          name: "U.S. Winner's Bracket",
+          roundMatchNumbers: {
+            "Opening Round": [1, 2, 3, 4],
+            "Winners Round 2": [1, 2],
+            "Winners Semifinals": [1, 2],
+            "Winners Final": [1],
+          },
+        },
+        {
+          name: "U.S. Elimination Bracket",
+          roundMatchNumbers: {
+            "Elimination Round 1": [1, 2],
+            "Elimination Round 2": [1, 2],
+            "Elimination Round 3": [1, 2],
+            "Elimination Round 4": [1],
+            "Elimination Final": [1],
+          },
+        },
+        {
+          name: "U.S. Championship",
+          roundMatchNumbers: { "Bracket Championship": [1] },
+        },
+      ],
+    },
+    {
+      name: "International",
+      groups: [
+        {
+          name: "International Winner's Bracket",
+          roundMatchNumbers: {
+            "Opening Round": [5, 6, 7, 8],
+            "Winners Round 2": [3, 4],
+            "Winners Semifinals": [3, 4],
+            "Winners Final": [2],
+          },
+        },
+        {
+          name: "International Elimination Bracket",
+          roundMatchNumbers: {
+            "Elimination Round 1": [3, 4],
+            "Elimination Round 2": [3, 4],
+            "Elimination Round 3": [3, 4],
+            "Elimination Round 4": [2],
+            "Elimination Final": [2],
+          },
+        },
+        {
+          name: "International Championship",
+          roundMatchNumbers: { "Bracket Championship": [2] },
+        },
+      ],
+    },
+    {
+      name: "Championship",
+      rounds: ["Consolation Third Place", "World Championship"],
+    },
+  ],
+};
+
 /**
  * All available bracket templates
  */
@@ -951,6 +1215,7 @@ export const BRACKET_TEMPLATES: Record<string, BracketTemplate> = {
   tennis_128: TENNIS_128,
   cfp_12: CFP_12,
   nba_20: NBA_20,
+  llws_20: LLWS_20,
 };
 
 /**
@@ -1006,6 +1271,18 @@ export function getScoringRoundType(
   const round = template.rounds.find((r) => r.name === roundName);
   if (!round || !round.isScoring) return null;
 
+  // Special handling for LLWS double elimination: match counts don't identify the
+  // tier (Elimination Round 4 and the Elimination Final both have 2 matches), and
+  // the Winners Final eliminates nobody.
+  if (template.id === "llws_20") {
+    if (roundName === "Elimination Round 4") return "quarterfinals"; // losers share 7-8th
+    if (roundName === "Elimination Final") return "quarterfinals";   // losers share 5-6th
+    if (roundName === "Bracket Championship") return "semifinals";   // losers play for 3-4th
+    if (roundName === "Consolation Third Place") return "semifinals"; // finalizes 3rd/4th
+    if (roundName === "World Championship") return "finals";         // 1st and 2nd
+    return null; // Winners Final: loser drops to the elimination bracket, nobody is out
+  }
+
   // Special handling for AFL finals
   if (template.id === "afl_10") {
     if (roundName === "Elimination Finals") return "quarterfinals"; // Losers share 7-8th

app/models/__tests__/llws-20-bracket.test.ts

@@ -0,0 +1,589 @@
+/**
+ * LLWS 20-Team Double-Elimination Bracket Tests
+ *
+ * Verifies the llws_20 template against the official 2026 LLBWS bracket
+ * (Williamsport, Aug 19–30). The PDF numbers its games 1–38; those numbers appear
+ * throughout as `G<n>` so the routing can be checked against the printed bracket.
+ *
+ * The critical property under test is the double-elimination loser routing: a loss in
+ * the winners bracket drops a team into the elimination bracket at a specific slot,
+ * while a loss in the elimination bracket is final.
+ */
+
+import { describe, it, expect, vi } from "vitest";
+import {
+  LLWS_20,
+  getScoringRoundType,
+  llwsMatchNumber,
+  llwsSideAndLocal,
+} from "~/lib/bracket-templates";
+import {
+  doesLoserAdvance,
+  generateBracketFromTemplate,
+  resolveLLWSAdvancement,
+} from "../playoff-match";
+import {
+  calculateBracketPoints,
+  calculateAveragedPoints,
+  type ScoringRules,
+} from "../scoring-rules";
+
+// generateBracketFromTemplate's only DB touch for llws_20 is the bulk insert, so a
+// minimal stub is enough to capture the generated rows.
+const insertedRows: Record<string, unknown>[] = [];
+vi.mock("~/database/context", () => ({
+  database: () => ({
+    insert: () => ({
+      values: (rows: Record<string, unknown>[]) => ({
+        returning: async () => {
+          insertedRows.push(...rows);
+          return rows;
+        },
+      }),
+    }),
+  }),
+}));
+
+const DEFAULT_SCORING: ScoringRules = {
+  pointsFor1st: 100,
+  pointsFor2nd: 70,
+  pointsFor3rd: 50,
+  pointsFor4th: 40,
+  pointsFor5th: 25,
+  pointsFor6th: 20,
+  pointsFor7th: 15,
+  pointsFor8th: 10,
+};
+
+// ── PDF game number ↔ (round, match number) ──────────────────────────────────
+//
+// Transcribed directly from the 2026 LLBWS bracket. U.S. games take the low match
+// numbers in each round, International the high ones.
+const GAME_TO_MATCH: Record<number, { round: string; matchNumber: number }> = {
+  // Opening Round — U.S. G2,4,6,8 (M1–4); Intl G1,3,5,7 (M5–8)
+  2: { round: "Opening Round", matchNumber: 1 },
+  4: { round: "Opening Round", matchNumber: 2 },
+  6: { round: "Opening Round", matchNumber: 3 },
+  8: { round: "Opening Round", matchNumber: 4 },
+  1: { round: "Opening Round", matchNumber: 5 },
+  3: { round: "Opening Round", matchNumber: 6 },
+  5: { round: "Opening Round", matchNumber: 7 },
+  7: { round: "Opening Round", matchNumber: 8 },
+  // Winners Round 2 — U.S. G10,12; Intl G9,11
+  10: { round: "Winners Round 2", matchNumber: 1 },
+  12: { round: "Winners Round 2", matchNumber: 2 },
+  9: { round: "Winners Round 2", matchNumber: 3 },
+  11: { round: "Winners Round 2", matchNumber: 4 },
+  // Elimination Round 1 — U.S. G14,16; Intl G13,15
+  14: { round: "Elimination Round 1", matchNumber: 1 },
+  16: { round: "Elimination Round 1", matchNumber: 2 },
+  13: { round: "Elimination Round 1", matchNumber: 3 },
+  15: { round: "Elimination Round 1", matchNumber: 4 },
+  // Winners Semifinals — U.S. G17,19; Intl G18,20
+  17: { round: "Winners Semifinals", matchNumber: 1 },
+  19: { round: "Winners Semifinals", matchNumber: 2 },
+  18: { round: "Winners Semifinals", matchNumber: 3 },
+  20: { round: "Winners Semifinals", matchNumber: 4 },
+  // Elimination Round 2 — U.S. G22,24; Intl G21,23
+  22: { round: "Elimination Round 2", matchNumber: 1 },
+  24: { round: "Elimination Round 2", matchNumber: 2 },
+  21: { round: "Elimination Round 2", matchNumber: 3 },
+  23: { round: "Elimination Round 2", matchNumber: 4 },
+  // Elimination Round 3 — U.S. G26,28; Intl G25,27
+  26: { round: "Elimination Round 3", matchNumber: 1 },
+  28: { round: "Elimination Round 3", matchNumber: 2 },
+  25: { round: "Elimination Round 3", matchNumber: 3 },
+  27: { round: "Elimination Round 3", matchNumber: 4 },
+  // Winners Final — U.S. G30; Intl G29
+  30: { round: "Winners Final", matchNumber: 1 },
+  29: { round: "Winners Final", matchNumber: 2 },
+  // Elimination Round 4 — U.S. G32; Intl G31
+  32: { round: "Elimination Round 4", matchNumber: 1 },
+  31: { round: "Elimination Round 4", matchNumber: 2 },
+  // Elimination Final — U.S. G34; Intl G33
+  34: { round: "Elimination Final", matchNumber: 1 },
+  33: { round: "Elimination Final", matchNumber: 2 },
+  // Bracket Championship — U.S. G36; Intl G35
+  36: { round: "Bracket Championship", matchNumber: 1 },
+  35: { round: "Bracket Championship", matchNumber: 2 },
+  // Finals
+  37: { round: "Consolation Third Place", matchNumber: 1 },
+  38: { round: "World Championship", matchNumber: 1 },
+};
+
+const MATCH_TO_GAME = new Map<string, number>(
+  Object.entries(GAME_TO_MATCH).map(([game, m]) => [
+    `${m.round}#${m.matchNumber}`,
+    Number(game),
+  ])
+);
+
+function gameNumberFor(round: string, matchNumber: number): number {
+  const game = MATCH_TO_GAME.get(`${round}#${matchNumber}`);
+  if (game === undefined) throw new Error(`No PDF game for ${round} #${matchNumber}`);
+  return game;
+}
+
+/** Narrows a destination that the test expects to exist. */
+function required<T>(destination: T | null): T {
+  if (destination === null) throw new Error("Expected a destination, got null");
+  return destination;
+}
+
+/** PDF game number a destination points at. */
+function destinationGame(
+  destination: { round: string; matchNumber: number } | null
+): number {
+  const d = required(destination);
+  return gameNumberFor(d.round, d.matchNumber);
+}
+
+/**
+ * The official bracket printed as feed labels: for each game, which prior game's
+ * winner (W) or loser (L) fills each slot. `null` = a team seeded in directly.
+ *
+ * Transcribed from the PDF. This is the source of truth the routing must reproduce.
+ */
+const EXPECTED_SLOTS: Record<number, [string | null, string | null]> = {
+  // Opening Round — all directly seeded
+  1: [null, null], 2: [null, null], 3: [null, null], 4: [null, null],
+  5: [null, null], 6: [null, null], 7: [null, null], 8: [null, null],
+  // Winners Round 2 — bye team, then an Opening Round winner
+  9: [null, "W1"], 10: [null, "W2"], 11: [null, "W3"], 12: [null, "W4"],
+  // Elimination Round 1
+  13: ["L3", "L5"], 14: ["L4", "L6"], 15: ["L1", "L7"], 16: ["L2", "L8"],
+  // Winners Semifinals
+  17: ["W6", "W10"], 18: ["W5", "W9"], 19: ["W12", "W8"], 20: ["W11", "W7"],
+  // Elimination Round 2
+  21: ["L9", "W13"], 22: ["L10", "W14"], 23: ["L11", "W15"], 24: ["L12", "W16"],
+  // Elimination Round 3 — cross-over
+  25: ["L18", "W23"], 26: ["L17", "W24"], 27: ["L20", "W21"], 28: ["L19", "W22"],
+  // Winners Final
+  29: ["W18", "W20"], 30: ["W17", "W19"],
+  // Elimination Round 4
+  31: ["W27", "W25"], 32: ["W28", "W26"],
+  // Elimination Final
+  33: ["L29", "W31"], 34: ["L30", "W32"],
+  // Bracket Championship
+  35: ["W29", "W33"], 36: ["W30", "W34"],
+  // Finals
+  37: ["L36", "L35"], 38: ["W36", "W35"],
+};
+
+describe("LLWS 20 Bracket Template", () => {
+  describe("Template structure", () => {
+    it("has correct identity and size", () => {
+      expect(LLWS_20.id).toBe("llws_20");
+      expect(LLWS_20.totalTeams).toBe(20);
+      expect(LLWS_20.scoringStartsAtRound).toBe("Winners Final");
+    });
+
+    it("has 12 rounds totalling 38 matches", () => {
+      expect(LLWS_20.rounds).toHaveLength(12);
+      const total = LLWS_20.rounds.reduce((sum, r) => sum + r.matchCount, 0);
+      expect(total).toBe(38);
+    });
+
+    it("has the expected match count per round", () => {
+      const counts = Object.fromEntries(
+        LLWS_20.rounds.map((r) => [r.name, r.matchCount])
+      );
+      expect(counts).toEqual({
+        "Opening Round": 8,
+        "Winners Round 2": 4,
+        "Elimination Round 1": 4,
+        "Winners Semifinals": 4,
+        "Elimination Round 2": 4,
+        "Elimination Round 3": 4,
+        "Winners Final": 2,
+        "Elimination Round 4": 2,
+        "Elimination Final": 2,
+        "Bracket Championship": 2,
+        "Consolation Third Place": 1,
+        "World Championship": 1,
+      });
+    });
+
+    it("marks exactly the point-awarding rounds as scoring", () => {
+      const scoring = LLWS_20.rounds.filter((r) => r.isScoring).map((r) => r.name);
+      expect(scoring).toEqual([
+        "Winners Final",
+        "Elimination Round 4",
+        "Elimination Final",
+        "Bracket Championship",
+        "Consolation Third Place",
+        "World Championship",
+      ]);
+    });
+
+    it("lists rounds in chronological order", () => {
+      // Elimination Round 1 (Aug 22) is played before Winners Semifinals (Aug 23).
+      const names = LLWS_20.rounds.map((r) => r.name);
+      expect(names.indexOf("Elimination Round 1")).toBeLessThan(
+        names.indexOf("Winners Semifinals")
+      );
+      expect(names.indexOf("Winners Final")).toBeLessThan(
+        names.indexOf("Elimination Final")
+      );
+    });
+
+    it("gives elimination-bracket winners a floor matching their real worst case", () => {
+      const byName = (n: string) => LLWS_20.rounds.find((r) => r.name === n);
+      // Winning Elim R3 only guarantees 7th (a loss in Elim R4 is the 7–8 tier),
+      // so the engine's default floor of 5 would overstate it.
+      expect(byName("Elimination Round 3")?.nonScoringWinnerFloor).toBe(7);
+      // Reaching the Winners Final guarantees 5th at worst.
+      expect(byName("Winners Semifinals")?.nonScoringWinnerFloor).toBe(5);
+      // Nothing is guaranteed earlier than that.
+      expect(byName("Opening Round")?.nonScoringWinnerFloor).toBeNull();
+      expect(byName("Winners Round 2")?.nonScoringWinnerFloor).toBeNull();
+      expect(byName("Elimination Round 1")?.nonScoringWinnerFloor).toBeNull();
+      expect(byName("Elimination Round 2")?.nonScoringWinnerFloor).toBeNull();
+    });
+
+    it("has 20 participant labels", () => {
+      expect(LLWS_20.participantLabels).toHaveLength(20);
+    });
+
+    it("splits display into U.S., International and Championship phases", () => {
+      expect(LLWS_20.phases?.map((p) => p.name)).toEqual([
+        "United States",
+        "International",
+        "Championship",
+      ]);
+    });
+
+    it("assigns every match to exactly one phase group", () => {
+      const claimed = new Map<string, number>();
+      for (const phase of LLWS_20.phases ?? []) {
+        for (const group of phase.groups ?? []) {
+          for (const [round, numbers] of Object.entries(group.roundMatchNumbers)) {
+            for (const n of numbers) {
+              const key = `${round}#${n}`;
+              claimed.set(key, (claimed.get(key) ?? 0) + 1);
+            }
+          }
+        }
+      }
+      // Every per-side match claimed exactly once (36 games; the 2 finals live in
+      // the Championship phase's plain round list, not in a group).
+      expect(claimed.size).toBe(36);
+      expect([...claimed.values()].every((c) => c === 1)).toBe(true);
+    });
+  });
+
+  describe("Bracket generation", () => {
+    const PARTICIPANTS = Array.from({ length: 20 }, (_, i) => `team-${i}`);
+
+    async function generate() {
+      insertedRows.length = 0;
+      await generateBracketFromTemplate("event-1", "llws_20", PARTICIPANTS);
+      return insertedRows.map((r) => ({
+        round: r.round as string,
+        matchNumber: r.matchNumber as number,
+        participant1Id: (r.participant1Id ?? null) as string | null,
+        participant2Id: (r.participant2Id ?? null) as string | null,
+        isScoring: r.isScoring as boolean,
+      }));
+    }
+
+    it("creates all 38 matches", async () => {
+      const rows = await generate();
+      expect(rows).toHaveLength(38);
+    });
+
+    it("creates the right number of matches per round", async () => {
+      const rows = await generate();
+      for (const round of LLWS_20.rounds) {
+        expect(
+          rows.filter((r) => r.round === round.name),
+          `${round.name} match count`
+        ).toHaveLength(round.matchCount);
+      }
+    });
+
+    it("numbers matches 1..n within each round", async () => {
+      const rows = await generate();
+      for (const round of LLWS_20.rounds) {
+        const numbers = rows
+          .filter((r) => r.round === round.name)
+          .map((r) => r.matchNumber)
+          .toSorted((a, b) => a - b);
+        expect(numbers).toEqual(
+          Array.from({ length: round.matchCount }, (_, i) => i + 1)
+        );
+      }
+    });
+
+    it("seeds the Opening Round two teams at a time, U.S. then International", async () => {
+      const rows = await generate();
+      const opening = rows
+        .filter((r) => r.round === "Opening Round")
+        .toSorted((a, b) => a.matchNumber - b.matchNumber);
+      // U.S. slots 0–7 fill matches 1–4; International slots 10–17 fill matches 5–8.
+      expect(opening.map((m) => [m.participant1Id, m.participant2Id])).toEqual([
+        ["team-0", "team-1"],
+        ["team-2", "team-3"],
+        ["team-4", "team-5"],
+        ["team-6", "team-7"],
+        ["team-10", "team-11"],
+        ["team-12", "team-13"],
+        ["team-14", "team-15"],
+        ["team-16", "team-17"],
+      ]);
+    });
+
+    it("seats the four bye teams in Winners Round 2 awaiting an opponent", async () => {
+      const rows = await generate();
+      const wr2 = rows
+        .filter((r) => r.round === "Winners Round 2")
+        .toSorted((a, b) => a.matchNumber - b.matchNumber);
+      expect(wr2.map((m) => [m.participant1Id, m.participant2Id])).toEqual([
+        ["team-8", null],
+        ["team-9", null],
+        ["team-18", null],
+        ["team-19", null],
+      ]);
+    });
+
+    it("uses each participant exactly once and leaves every other slot empty", async () => {
+      const rows = await generate();
+      const seeded = rows
+        .flatMap((r) => [r.participant1Id, r.participant2Id])
+        .filter((id): id is string => id !== null);
+      expect(seeded).toHaveLength(20);
+      expect(new Set(seeded).size).toBe(20);
+      expect(new Set(seeded)).toEqual(new Set(PARTICIPANTS));
+    });
+
+    it("stamps isScoring from the template", async () => {
+      const rows = await generate();
+      for (const round of LLWS_20.rounds) {
+        for (const row of rows.filter((r) => r.round === round.name)) {
+          expect(row.isScoring, `${round.name} #${row.matchNumber}`).toBe(round.isScoring);
+        }
+      }
+    });
+
+    it("rejects a participant count other than 20", async () => {
+      await expect(
+        generateBracketFromTemplate("event-1", "llws_20", PARTICIPANTS.slice(0, 19))
+      ).rejects.toThrow(/requires 20 participants/);
+    });
+  });
+
+  describe("Side / match-number mapping", () => {
+    it("round-trips every match number through side-local form", () => {
+      for (const round of LLWS_20.rounds) {
+        if (round.matchCount === 1) continue; // shared finals have no side
+        for (let n = 1; n <= round.matchCount; n++) {
+          const { side, localMatch } = llwsSideAndLocal(round.name, n);
+          expect(llwsMatchNumber(round.name, side, localMatch)).toBe(n);
+        }
+      }
+    });
+
+    it("puts U.S. matches in the low half and International in the high half", () => {
+      expect(llwsSideAndLocal("Opening Round", 4).side).toBe(0);
+      expect(llwsSideAndLocal("Opening Round", 5).side).toBe(1);
+      expect(llwsSideAndLocal("Winners Semifinals", 2).side).toBe(0);
+      expect(llwsSideAndLocal("Winners Semifinals", 3).side).toBe(1);
+      expect(llwsSideAndLocal("Winners Final", 1).side).toBe(0);
+      expect(llwsSideAndLocal("Winners Final", 2).side).toBe(1);
+    });
+  });
+
+  describe("Advancement matches the official bracket", () => {
+    /**
+     * Replay the whole tournament through resolveLLWSAdvancement and record which
+     * feed label ends up in each slot, then compare against the printed bracket.
+     */
+    const actualSlots: Record<number, [string | null, string | null]> = {};
+    for (const game of Object.keys(EXPECTED_SLOTS)) {
+      actualSlots[Number(game)] = [null, null];
+    }
+
+    for (const [gameStr, { round, matchNumber }] of Object.entries(GAME_TO_MATCH)) {
+      const game = Number(gameStr);
+      const { winner, loser } = resolveLLWSAdvancement(round, matchNumber);
+      for (const [dest, label] of [
+        [winner, `W${game}`],
+        [loser, `L${game}`],
+      ] as const) {
+        if (!dest) continue;
+        const targetGame = gameNumberFor(dest.round, dest.matchNumber);
+        const slotIndex = dest.slot === "participant1Id" ? 0 : 1;
+        actualSlots[targetGame][slotIndex] = label;
+      }
+    }
+
+    it.each(Object.keys(EXPECTED_SLOTS).map(Number).toSorted((a, b) => a - b))(
+      "Game %i has the printed participants",
+      (game) => {
+        expect(actualSlots[game]).toEqual(EXPECTED_SLOTS[game]);
+      }
+    );
+
+    it("fills every slot in the bracket exactly once", () => {
+      // 38 games × 2 slots = 76. 20 are seeded directly (16 opening teams + 4 byes),
+      // leaving 56 to be filled by advancement.
+      const filled = Object.values(actualSlots)
+        .flat()
+        .filter((s) => s !== null).length;
+      expect(filled).toBe(56);
+    });
+  });
+
+  describe("Double-elimination loser routing", () => {
+    it("routes every winners-bracket loser into the elimination bracket", () => {
+      const winnersRounds = [
+        "Opening Round",
+        "Winners Round 2",
+        "Winners Semifinals",
+        "Winners Final",
+      ];
+      for (const roundName of winnersRounds) {
+        const round = LLWS_20.rounds.find((r) => r.name === roundName);
+        if (!round) throw new Error(`missing round ${roundName}`);
+        for (let n = 1; n <= round.matchCount; n++) {
+          const { loser } = resolveLLWSAdvancement(roundName, n);
+          expect(loser, `${roundName} #${n} loser should advance`).not.toBeNull();
+          expect(loser?.round.startsWith("Elimination")).toBe(true);
+        }
+      }
+    });
+
+    it("eliminates every elimination-bracket loser", () => {
+      const elimRounds = [
+        "Elimination Round 1",
+        "Elimination Round 2",
+        "Elimination Round 3",
+        "Elimination Round 4",
+        "Elimination Final",
+      ];
+      for (const roundName of elimRounds) {
+        const round = LLWS_20.rounds.find((r) => r.name === roundName);
+        if (!round) throw new Error(`missing round ${roundName}`);
+        for (let n = 1; n <= round.matchCount; n++) {
+          const { loser } = resolveLLWSAdvancement(roundName, n);
+          expect(loser, `${roundName} #${n} loser should be out`).toBeNull();
+        }
+      }
+    });
+
+    it("keeps the winners-bracket final loser alive via the Elimination Final", () => {
+      // G30 (U.S. Winners Final) loser → G34, not out. This is the defining
+      // double-elimination behavior: a first loss never eliminates.
+      const { winner, loser } = resolveLLWSAdvancement("Winners Final", 1);
+      expect(destinationGame(loser)).toBe(34);
+      expect(destinationGame(winner)).toBe(36);
+    });
+
+    it("sends the side-championship loser to the consolation game, not out", () => {
+      // No "if necessary" rematch: the winners-bracket champion that loses G36 is
+      // done in the bracket, but still plays G37 for 3rd/4th.
+      const us = resolveLLWSAdvancement("Bracket Championship", 1);
+      expect(destinationGame(us.winner)).toBe(38);
+      expect(destinationGame(us.loser)).toBe(37);
+      expect(required(us.winner).slot).toBe("participant1Id");
+      expect(required(us.loser).slot).toBe("participant1Id");
+
+      const intl = resolveLLWSAdvancement("Bracket Championship", 2);
+      expect(required(intl.winner).slot).toBe("participant2Id");
+      expect(required(intl.loser).slot).toBe("participant2Id");
+    });
+
+    it("flags winners-bracket losers as advancing so they are not marked eliminated", () => {
+      // doesLoserAdvance is what stops the scoring engine writing a 0-point
+      // elimination (and announcing a knockout) for a team that is still alive.
+      // Winners Final and Bracket Championship are scoring rounds and are covered
+      // by loserIsPartial instead, so they are deliberately not listed here.
+      for (const round of ["Opening Round", "Winners Round 2", "Winners Semifinals"]) {
+        expect(doesLoserAdvance(round, 1, "llws_20"), round).toBe(true);
+      }
+      for (const round of [
+        "Elimination Round 1",
+        "Elimination Round 2",
+        "Elimination Round 3",
+        "Elimination Round 4",
+        "Elimination Final",
+      ]) {
+        expect(doesLoserAdvance(round, 1, "llws_20"), round).toBe(false);
+      }
+    });
+
+    it("does not apply LLWS loser routing to other templates", () => {
+      expect(doesLoserAdvance("Opening Round", 1, "ncaa_68")).toBe(false);
+      expect(doesLoserAdvance("Winners Semifinals", 1, "")).toBe(false);
+    });
+
+    it("advances nobody out of the two final games", () => {
+      for (const round of ["Consolation Third Place", "World Championship"]) {
+        expect(resolveLLWSAdvancement(round, 1)).toEqual({ winner: null, loser: null });
+      }
+    });
+
+    it("never crosses a team between the U.S. and International sides", () => {
+      for (const round of LLWS_20.rounds) {
+        if (round.name === "Bracket Championship") continue; // the crossover point
+        if (round.matchCount === 1) continue;
+        for (let n = 1; n <= round.matchCount; n++) {
+          const { side } = llwsSideAndLocal(round.name, n);
+          const { winner, loser } = resolveLLWSAdvancement(round.name, n);
+          for (const dest of [winner, loser]) {
+            if (!dest) continue;
+            const destRound = LLWS_20.rounds.find((r) => r.name === dest.round);
+            if (!destRound || destRound.matchCount === 1) continue;
+            expect(llwsSideAndLocal(dest.round, dest.matchNumber).side).toBe(side);
+          }
+        }
+      }
+    });
+  });
+
+  describe("Placement tiers", () => {
+    it("classifies scoring rounds correctly", () => {
+      expect(getScoringRoundType("Elimination Round 4", LLWS_20)).toBe("quarterfinals");
+      expect(getScoringRoundType("Elimination Final", LLWS_20)).toBe("quarterfinals");
+      expect(getScoringRoundType("Bracket Championship", LLWS_20)).toBe("semifinals");
+      expect(getScoringRoundType("World Championship", LLWS_20)).toBe("finals");
+      // Nobody is eliminated in the Winners Final — the loser drops to the
+      // elimination bracket — so it has no placement tier.
+      expect(getScoringRoundType("Winners Final", LLWS_20)).toBeNull();
+    });
+
+    it("pays 3rd and 4th distinctly (there is a real consolation game)", () => {
+      expect(calculateBracketPoints(3, DEFAULT_SCORING, "llws_20")).toBe(50);
+      expect(calculateBracketPoints(4, DEFAULT_SCORING, "llws_20")).toBe(40);
+    });
+
+    it("splits 5–8 into two two-team tiers", () => {
+      const upper = calculateAveragedPoints([5, 6], DEFAULT_SCORING); // (25+20)/2
+      const lower = calculateAveragedPoints([7, 8], DEFAULT_SCORING); // (15+10)/2
+      expect(calculateBracketPoints(5, DEFAULT_SCORING, "llws_20")).toBe(upper);
+      expect(calculateBracketPoints(6, DEFAULT_SCORING, "llws_20")).toBe(upper);
+      expect(calculateBracketPoints(7, DEFAULT_SCORING, "llws_20")).toBe(lower);
+      expect(calculateBracketPoints(8, DEFAULT_SCORING, "llws_20")).toBe(lower);
+      // Surviving Elimination Round 4 is worth more than losing it.
+      expect(upper).toBeGreaterThan(lower);
+    });
+
+    it("awards nothing below 8th", () => {
+      // The 12 teams knocked out in Elimination Rounds 1–3 finish 9th–20th.
+      expect(calculateBracketPoints(9, DEFAULT_SCORING, "llws_20")).toBe(0);
+      expect(calculateBracketPoints(0, DEFAULT_SCORING, "llws_20")).toBe(0);
+    });
+
+    it("has exactly 8 teams alive when the first scoring elimination game is played", () => {
+      // Elimination Round 4 is the 7th–8th tier, so the field must be 8 at that point:
+      // per side the Winners Final winner, the Winners Final loser, and the two
+      // Elimination Round 3 winners.
+      const eliminatedBeforeElimR4 =
+        (LLWS_20.rounds.find((r) => r.name === "Elimination Round 1")?.matchCount ?? 0) +
+        (LLWS_20.rounds.find((r) => r.name === "Elimination Round 2")?.matchCount ?? 0) +
+        (LLWS_20.rounds.find((r) => r.name === "Elimination Round 3")?.matchCount ?? 0);
+      expect(eliminatedBeforeElimR4).toBe(12);
+      expect(LLWS_20.totalTeams - eliminatedBeforeElimR4).toBe(8);
+    });
+  });
+});

app/models/playoff-match.ts

@@ -6,6 +6,8 @@ import {
   getBracketTemplate,
   buildNCAA68SlotMap,
   matchIndexForSeedSlot,
+  llwsMatchNumber,
+  llwsSideAndLocal,
   STANDARD_BRACKET_SEEDING,
 } from "~/lib/bracket-templates";
 
@@ -467,6 +469,11 @@ export async function generateBracketFromTemplate(
     return await generateNBA20Bracket(eventId, template, participantIds);
   }
 
+  // LLWS 20 requires special handling for its two double-elimination brackets
+  if (templateId === "llws_20") {
+    return await generateLLWS20Bracket(eventId, template, participantIds);
+  }
+
   const matches: NewPlayoffMatch[] = [];
 
   // Generate matches for each round in the template
@@ -980,6 +987,15 @@ export async function advanceWinnerTemplate(
     return await advanceNBAPlayInWinner(match, winnerId, loserId);
   }
 
+  // Special handling for LLWS 20 double elimination: winners-bracket losers route
+  // into the elimination bracket instead of being knocked out.
+  if (template.id === "llws_20") {
+    const loserId =
+      match.participant1Id === winnerId ? match.participant2Id : match.participant1Id;
+    if (!loserId) throw new Error("Cannot determine loser for LLWS advancement");
+    return await advanceLLWSWinner(match, winnerId, loserId);
+  }
+
   // Special handling for AFL 10 double-chance system
   // Phase 3.3: AFL has complex winner/loser advancement rules
   if (template.id === "afl_10") {
@@ -1427,6 +1443,12 @@ export function doesLoserAdvance(
   if (templateId === "afl_10" && round === "Qualifying Finals") {
     return true;
   }
+  // LLWS winners bracket: a loss drops the team into the elimination bracket, so it
+  // must not be recorded as an elimination. (Winners Final and Bracket Championship
+  // are scoring rounds and are handled via loserIsPartial instead.)
+  if (templateId === "llws_20" && LLWS_LOSER_ADVANCES_ROUNDS.has(round)) {
+    return true;
+  }
   return false;
 }
 
@@ -1538,3 +1560,320 @@ async function advanceNBAPlayInWinner(
     throw new Error(`Unknown Play-In Round 2 match number: ${match.matchNumber}`);
   }
 }
+
+// ── LLWS 20 (double elimination) ──────────────────────────────────────────────
+
+/**
+ * Where one participant goes after an LLWS match: a round, a side-local match number,
+ * and which slot to fill. `null` means eliminated (or, for winners, no further game).
+ */
+interface LLWSDestination {
+  round: string;
+  localMatch: number;
+  slot: "participant1Id" | "participant2Id";
+}
+
+/**
+ * LLWS advancement map, in SIDE-LOCAL match numbers.
+ *
+ * Keyed by round, then by the local match number of the completed game. Each entry
+ * says where the winner goes and where the loser goes (null = eliminated).
+ *
+ * Verified game-by-game against the official 2026 LLBWS bracket. Note the deliberate
+ * cross-overs — the elimination bracket does NOT feed straight across:
+ *   Elim R1:  L(Opening m2) v L(Opening m3)  and  L(Opening m1) v L(Opening m4)
+ *   Elim R3:  L(Semi m1) v W(Elim R2 m2)     and  L(Semi m2) v W(Elim R2 m1)
+ *   Elim R4:  W(Elim R3 m1) v W(Elim R3 m2)
+ *
+ * A loss in the winners bracket routes into the elimination bracket rather than
+ * eliminating the team; a loss in the elimination bracket is final.
+ */
+const LLWS_ADVANCEMENT: Record<
+  string,
+  Record<number, { winner: LLWSDestination | null; loser: LLWSDestination | null }>
+> = {
+  "Opening Round": {
+    1: {
+      winner: { round: "Winners Round 2", localMatch: 1, slot: "participant2Id" },
+      loser: { round: "Elimination Round 1", localMatch: 2, slot: "participant1Id" },
+    },
+    2: {
+      winner: { round: "Winners Round 2", localMatch: 2, slot: "participant2Id" },
+      loser: { round: "Elimination Round 1", localMatch: 1, slot: "participant1Id" },
+    },
+    3: {
+      winner: { round: "Winners Semifinals", localMatch: 1, slot: "participant1Id" },
+      loser: { round: "Elimination Round 1", localMatch: 1, slot: "participant2Id" },
+    },
+    4: {
+      winner: { round: "Winners Semifinals", localMatch: 2, slot: "participant2Id" },
+      loser: { round: "Elimination Round 1", localMatch: 2, slot: "participant2Id" },
+    },
+  },
+  "Winners Round 2": {
+    1: {
+      winner: { round: "Winners Semifinals", localMatch: 1, slot: "participant2Id" },
+      loser: { round: "Elimination Round 2", localMatch: 1, slot: "participant1Id" },
+    },
+    2: {
+      winner: { round: "Winners Semifinals", localMatch: 2, slot: "participant1Id" },
+      loser: { round: "Elimination Round 2", localMatch: 2, slot: "participant1Id" },
+    },
+  },
+  "Winners Semifinals": {
+    1: {
+      winner: { round: "Winners Final", localMatch: 1, slot: "participant1Id" },
+      loser: { round: "Elimination Round 3", localMatch: 1, slot: "participant1Id" },
+    },
+    2: {
+      winner: { round: "Winners Final", localMatch: 1, slot: "participant2Id" },
+      loser: { round: "Elimination Round 3", localMatch: 2, slot: "participant1Id" },
+    },
+  },
+  "Winners Final": {
+    1: {
+      winner: { round: "Bracket Championship", localMatch: 1, slot: "participant1Id" },
+      // A winners-bracket final loss is not an elimination — it drops to the
+      // Elimination Final for a second chance at the side championship.
+      loser: { round: "Elimination Final", localMatch: 1, slot: "participant1Id" },
+    },
+  },
+  "Elimination Round 1": {
+    1: {
+      winner: { round: "Elimination Round 2", localMatch: 1, slot: "participant2Id" },
+      loser: null,
+    },
+    2: {
+      winner: { round: "Elimination Round 2", localMatch: 2, slot: "participant2Id" },
+      loser: null,
+    },
+  },
+  "Elimination Round 2": {
+    // Cross-over: R2 m1's winner meets the OTHER semifinal loser.
+    1: {
+      winner: { round: "Elimination Round 3", localMatch: 2, slot: "participant2Id" },
+      loser: null,
+    },
+    2: {
+      winner: { round: "Elimination Round 3", localMatch: 1, slot: "participant2Id" },
+      loser: null,
+    },
+  },
+  "Elimination Round 3": {
+    // The later game (m2) is printed on top: G32 = W28 v W26, G31 = W27 v W25.
+    1: {
+      winner: { round: "Elimination Round 4", localMatch: 1, slot: "participant2Id" },
+      loser: null,
+    },
+    2: {
+      winner: { round: "Elimination Round 4", localMatch: 1, slot: "participant1Id" },
+      loser: null,
+    },
+  },
+  "Elimination Round 4": {
+    1: {
+      winner: { round: "Elimination Final", localMatch: 1, slot: "participant2Id" },
+      loser: null,
+    },
+  },
+  "Elimination Final": {
+    1: {
+      winner: { round: "Bracket Championship", localMatch: 1, slot: "participant2Id" },
+      loser: null,
+    },
+  },
+};
+
+/** Rounds whose losers drop into the elimination bracket instead of going out. */
+const LLWS_LOSER_ADVANCES_ROUNDS = new Set([
+  "Opening Round",
+  "Winners Round 2",
+  "Winners Semifinals",
+]);
+
+/** A resolved LLWS destination, in global (not side-local) match numbers. */
+export interface LLWSResolvedDestination {
+  round: string;
+  matchNumber: number;
+  slot: "participant1Id" | "participant2Id";
+}
+
+/**
+ * Resolve where the winner and loser of a completed LLWS match go, in global match
+ * numbers. `null` means that participant has no further game (eliminated, or the
+ * tournament is over for them).
+ *
+ * Pure — no DB access — so the whole 38-game routing can be verified against the
+ * official bracket in tests. advanceLLWSWinner is a thin writer on top of this.
+ */
+export function resolveLLWSAdvancement(
+  round: string,
+  matchNumber: number
+): { winner: LLWSResolvedDestination | null; loser: LLWSResolvedDestination | null } {
+  // Terminal rounds — nobody advances.
+  if (round === "Consolation Third Place" || round === "World Championship") {
+    return { winner: null, loser: null };
+  }
+
+  // Bracket Championship is the crossover: the winner goes to the World Championship
+  // and the loser to the Consolation game. The side fixes the slot in both (U.S. takes
+  // participant1, International participant2), so the two sides can't collide.
+  if (round === "Bracket Championship") {
+    const { side } = llwsSideAndLocal("Bracket Championship", matchNumber);
+    const slot: "participant1Id" | "participant2Id" =
+      side === 0 ? "participant1Id" : "participant2Id";
+    return {
+      winner: { round: "World Championship", matchNumber: 1, slot },
+      loser: { round: "Consolation Third Place", matchNumber: 1, slot },
+    };
+  }
+
+  const roundMap = LLWS_ADVANCEMENT[round];
+  if (!roundMap) {
+    throw new Error(`Round '${round}' is not part of the LLWS bracket`);
+  }
+
+  const { side, localMatch } = llwsSideAndLocal(round, matchNumber);
+  const routes = roundMap[localMatch];
+  if (!routes) {
+    throw new Error(`No LLWS advancement defined for ${round} match ${matchNumber}`);
+  }
+
+  // Winner and loser stay on their own side, so the same side offset applies to both.
+  const toGlobal = (d: LLWSDestination | null): LLWSResolvedDestination | null =>
+    d === null
+      ? null
+      : { round: d.round, matchNumber: llwsMatchNumber(d.round, side, d.localMatch), slot: d.slot };
+
+  return { winner: toGlobal(routes.winner), loser: toGlobal(routes.loser) };
+}
+
+/**
+ * Generate the 20-team LLWS double-elimination bracket (38 matches).
+ *
+ * Only the Opening Round and the four bye slots receive participants up front;
+ * everything else is filled by advanceLLWSWinner as games complete.
+ *
+ * Participant array layout (see LLWS_20 in lib/bracket-templates):
+ *   [0–7]   U.S. Opening Round teams, two per game
+ *   [8, 9]  U.S. bye teams → Winners Round 2 M1 / M2 participant1
+ *   [10–17] International Opening Round teams, two per game
+ *   [18,19] International bye teams → Winners Round 2 M3 / M4 participant1
+ */
+async function generateLLWS20Bracket(
+  eventId: string,
+  template: BracketTemplate,
+  participantIds?: string[]
+): Promise<PlayoffMatch[]> {
+  const matches: NewPlayoffMatch[] = [];
+  const p = (idx: number): string | null =>
+    participantIds ? (participantIds[idx] ?? null) : null;
+
+  const sides = [
+    { side: 0 as const, label: "U.S.", openingBase: 0, byeBase: 8 },
+    { side: 1 as const, label: "Intl", openingBase: 10, byeBase: 18 },
+  ];
+
+  // ── Opening Round: 4 games per side, both slots seeded ──────────────────────
+  for (const { side, label, openingBase } of sides) {
+    for (let local = 1; local <= 4; local++) {
+      matches.push({
+        scoringEventId: eventId,
+        round: "Opening Round",
+        matchNumber: llwsMatchNumber("Opening Round", side, local),
+        participant1Id: p(openingBase + (local - 1) * 2),
+        participant2Id: p(openingBase + (local - 1) * 2 + 1),
+        isComplete: false,
+        isScoring: false,
+        templateRound: "Opening Round",
+        seedInfo: `${label} Opening ${local}`,
+      });
+    }
+  }
+
+  // ── Winners Round 2: bye team at participant1, Opening winner at participant2 ─
+  for (const { side, label, byeBase } of sides) {
+    for (let local = 1; local <= 2; local++) {
+      matches.push({
+        scoringEventId: eventId,
+        round: "Winners Round 2",
+        matchNumber: llwsMatchNumber("Winners Round 2", side, local),
+        participant1Id: p(byeBase + (local - 1)),
+        participant2Id: null, // Opening Round winner
+        isComplete: false,
+        isScoring: false,
+        templateRound: "Winners Round 2",
+        seedInfo: `${label} Bye ${local} vs Opening ${local} winner`,
+      });
+    }
+  }
+
+  // ── Every remaining round starts empty ──────────────────────────────────────
+  const remaining = template.rounds.filter(
+    (r) => r.name !== "Opening Round" && r.name !== "Winners Round 2"
+  );
+  for (const round of remaining) {
+    for (let i = 1; i <= round.matchCount; i++) {
+      // Championship/Consolation are single shared games; everything else is per-side.
+      const perSide = round.matchCount > 1;
+      const label = perSide
+        ? llwsSideAndLocal(round.name, i).side === 0
+          ? "U.S."
+          : "Intl"
+        : null;
+      matches.push({
+        scoringEventId: eventId,
+        round: round.name,
+        matchNumber: i,
+        participant1Id: null,
+        participant2Id: null,
+        isComplete: false,
+        isScoring: round.isScoring,
+        templateRound: round.name,
+        seedInfo: label ? `${label} ${round.name}` : null,
+      });
+    }
+  }
+
+  return await createManyPlayoffMatches(matches);
+}
+
+/**
+ * LLWS advancement: routes the winner forward and, in the winners bracket, routes the
+ * loser into the elimination bracket rather than eliminating them.
+ *
+ * All routing decisions live in resolveLLWSAdvancement; this function only writes.
+ */
+async function advanceLLWSWinner(
+  match: PlayoffMatch,
+  winnerId: string,
+  loserId: string
+): Promise<void> {
+  const eventId = match.scoringEventId;
+  const { winner, loser } = resolveLLWSAdvancement(match.round, match.matchNumber);
+
+  // Winner and loser can land in different rounds, so resolve each independently.
+  const moves: Array<{ destination: LLWSResolvedDestination; participantId: string }> = [];
+  if (winner) moves.push({ destination: winner, participantId: winnerId });
+  if (loser) moves.push({ destination: loser, participantId: loserId });
+
+  for (const { destination, participantId } of moves) {
+    const targetMatches = await findPlayoffMatchesByEventIdAndRound(
+      eventId,
+      destination.round
+    );
+    const target = targetMatches.find((m) => m.matchNumber === destination.matchNumber);
+    if (!target) {
+      throw new Error(
+        `Next match not found: round=${destination.round}, matchNumber=${destination.matchNumber}`
+      );
+    }
+    if (target[destination.slot]) {
+      throw new Error(
+        `Next match ${destination.slot} is already filled ` +
+        `(round=${destination.round}, matchNumber=${destination.matchNumber})`
+      );
+    }
+    await updatePlayoffMatch(target.id, { [destination.slot]: participantId });
+  }
+}

app/models/scoring-calculator.ts

@@ -113,6 +113,21 @@ const TEMPLATE_ROUND_CONFIG: Record<string, Record<string, RoundScoringConfig>>
     // 3rd place game finalizes both positions distinctly.
     "Third Place Game":  { loserPosition: 4, loserIsPartial: false, winnerFloor: null, winnerPosition: 3 },
   },
+  llws_20: {
+    // Winners Final loser drops to the Elimination Final, so 5th is provisional —
+    // winning that game lifts them back to a 4th-place floor.
+    "Winners Final":           { loserPosition: 5, loserIsPartial: true,  winnerFloor: 4 },
+    // Elimination Round 4 losers are the 7th–8th tier (8 teams alive at this point).
+    "Elimination Round 4":     { loserPosition: 7, loserIsPartial: false, winnerFloor: 5 },
+    // Elimination Final losers are the 5th–6th tier; the winner reaches the side
+    // championship, where the worst case is 4th (lose it, then lose the consolation).
+    "Elimination Final":       { loserPosition: 5, loserIsPartial: false, winnerFloor: 4 },
+    // Side championship loser still has the consolation game — provisional 4th.
+    "Bracket Championship":    { loserPosition: 4, loserIsPartial: true,  winnerFloor: 2 },
+    // Consolation finalizes 3rd and 4th distinctly.
+    "Consolation Third Place": { loserPosition: 4, loserIsPartial: false, winnerFloor: null, winnerPosition: 3 },
+    "World Championship":      { loserPosition: 2, loserIsPartial: false, winnerFloor: null },
+  },
   tennis_128: {
     // R16 losers share 9th–16th; winner advances to QF (floor 5th–8th).
     "Round of 16":  { loserPosition: 9, loserIsPartial: false, winnerFloor: 5 },
@@ -126,28 +141,37 @@ const TEMPLATE_ROUND_CONFIG: Record<string, Record<string, RoundScoringConfig>>
 };
 
 /**
- * Returns true if a non-scoring round's winners are entering the first scoring round
+ * Returns the floor position that winners of a NON-scoring round should bank, or null
- * (i.e., they've guaranteed a top-8 fantasy placement and should receive a T5–T8 floor).
+ * to bank nothing.
  *
- * For multi-round pre-bracket sequences like NCAA (Round of 64 → Round of 32 →
+ * Default: winners entering the first scoring round have guaranteed a top-8 fantasy
- * Sweet Sixteen → Elite Eight), only Sweet Sixteen winners are entering the scoring
+ * placement and receive a T5–T8 floor (5); everyone else gets nothing yet. For
- * bracket — Round of 64 and Round of 32 winners should not receive any floor yet.
+ * multi-round pre-bracket sequences like NCAA (Round of 64 → Round of 32 → Sweet
+ * Sixteen → Elite Eight), only Sweet Sixteen winners are entering the scoring bracket.
  *
- * Falls back to true when template/round info is unavailable to preserve legacy behavior.
+ * A round may override this with `nonScoringWinnerFloor` when the default is wrong —
+ * in a double-elimination losers bracket a win can guarantee a worse finish than 5th
+ * (llws_20 "Elimination Round 3" → 7), or nothing at all.
+ *
+ * Falls back to 5 when template/round info is unavailable, preserving legacy behavior.
  */
-function doesNonScoringRoundFeedIntoScoringRound(
+function nonScoringWinnerFloorFor(
   round: string,
   bracketTemplateId: string | null | undefined
-): boolean {
+): number | null {
-  if (!bracketTemplateId) return true; // Legacy: preserve old behavior
+  if (!bracketTemplateId) return 5; // Legacy: preserve old behavior
   const template = BRACKET_TEMPLATES[bracketTemplateId];
-  if (!template) return true; // Unknown template: preserve old behavior
+  if (!template) return 5; // Unknown template: preserve old behavior
   const currentRound = template.rounds.find((r) => r.name === round);
-  if (!currentRound) return true; // Unknown round: preserve old behavior
+  if (!currentRound) return 5; // Unknown round: preserve old behavior
+  // Explicit per-round override wins, including an explicit null (bank nothing).
+  if (currentRound.nonScoringWinnerFloor !== undefined) {
+    return currentRound.nonScoringWinnerFloor;
+  }
   const nextRoundName = currentRound.feedsInto;
-  if (!nextRoundName) return false; // No next round (shouldn't happen for non-scoring)
+  if (!nextRoundName) return null; // No next round (shouldn't happen for non-scoring)
   const nextRound = template.rounds.find((r) => r.name === nextRoundName);
-  return nextRound?.isScoring === true;
+  return nextRound?.isScoring === true ? 5 : null;
 }
 
 /**
@@ -281,19 +305,18 @@ export async function processPlayoffEvent(
   }
 
   if (!isScoring) {
-    // Non-scoring (pre-bracket) round: losers are permanently eliminated (0 pts).
+    // Non-scoring round: losers are permanently eliminated (0 pts) unless they
-    // Winners only bank a provisional T5–T8 floor if they're entering the first
+    // advance (double-elimination winners-bracket losers). Winners bank a
-    // scoring round (i.e., guaranteed top-8). For multi-round pre-bracket sequences
+    // provisional floor only when this round guarantees them one — see
-    // like NCAA (R64 → R32 → Sweet 16 → Elite Eight), only Sweet 16 winners should
+    // nonScoringWinnerFloorFor for how that is derived per template.
-    // receive floor points — R64 and R32 winners are not yet guaranteed top-8.
+    const winnerFloor = nonScoringWinnerFloorFor(round, event.bracketTemplateId);
-    const awardFloor = doesNonScoringRoundFeedIntoScoringRound(round, event.bracketTemplateId);
     for (const match of matches) {
       const loserAdvances = doesLoserAdvance(round, match.matchNumber, event.bracketTemplateId ?? "");
       if (match.loserId && !loserAdvances) {
         await upsertParticipantResult(match.loserId, event.sportsSeasonId, 0, db);
       }
-      if (match.winnerId && awardFloor) {
+      if (match.winnerId && winnerFloor !== null) {
-        await upsertParticipantResult(match.winnerId, event.sportsSeasonId, 5, db, true);
+        await upsertParticipantResult(match.winnerId, event.sportsSeasonId, winnerFloor, db, true);
       }
     }
   } else {
@@ -353,7 +376,7 @@ export async function processPlayoffEvent(
   // Progressive floor scoring: assign guaranteed minimum points to winners.
   // For Finals (winnerFloor=null) getGuaranteedMinimumPosition returns null — the
   // winner is already finalized as 1st above. For non-scoring rounds it also
-  // returns null (winners were given floor 5 inline above).
+  // returns null; those winners were given their floor inline above.
   const guaranteedMinimum = getGuaranteedMinimumPosition(
     round,
     event.bracketTemplateId,
@@ -441,8 +464,9 @@ export async function processMatchResult(
     if (!loserAdvances) {
       await upsertParticipantResult(loserId, sportsSeasonId, 0, db);
     }
-    if (doesNonScoringRoundFeedIntoScoringRound(round, bracketTemplateId)) {
+    const nonScoringFloor = nonScoringWinnerFloorFor(round, bracketTemplateId);
-      await upsertParticipantResult(winnerId, sportsSeasonId, 5, db, true);
+    if (nonScoringFloor !== null) {
+      await upsertParticipantResult(winnerId, sportsSeasonId, nonScoringFloor, db, true);
     }
     // Non-scoring round wins are not surfaced in the Recent Scores feed.
   } else {

app/models/scoring-rules.ts

@@ -134,14 +134,21 @@ export function calculateSharedPlacementPoints(
  * AFL is different: it has TWO distinct tiers in the 5–8 zone:
  *   - T5-T6: Semi-Finals losers (positions 5 and 6) → avg([5,6])
  *   - T7-T8: Elimination Finals losers (positions 7 and 8) → avg([7,8])
+ *
+ * LLWS has the same shape from its two elimination brackets:
+ *   - T5-T6: Elimination Final losers (one per side) → avg([5,6])
+ *   - T7-T8: Elimination Round 4 losers (one per side) → avg([7,8])
  */
-const SPLIT_5678_TEMPLATE_IDS = new Set(["afl_10"]);
+const SPLIT_5678_TEMPLATE_IDS = new Set(["afl_10", "llws_20"]);
 
 /**
  * Brackets with a real 3rd place game, meaning positions 3 and 4 are distinct
  * (not averaged). Standard brackets average them because both SF losers tie.
+ *
+ * llws_20's Consolation Third Place game decides 3rd and 4th head-to-head between
+ * the two side runners-up.
  */
-const DISTINCT_34_TEMPLATE_IDS = new Set(["fifa_48"]);
+const DISTINCT_34_TEMPLATE_IDS = new Set(["fifa_48", "llws_20"]);
 
 /**
  * Calculate fantasy points for a bracket placement, averaging tied positions.

app/routes/admin.sports-seasons.$id.events.$eventId.bracket.tsx

@@ -889,7 +889,7 @@ export default function EventBracket({
                         return (
                           // eslint-disable-next-line react/no-array-index-key
                           <div key={i} className="flex items-center gap-2">
-                            <Label className="w-20 text-sm text-muted-foreground shrink-0">
+                            <Label className="w-28 text-sm text-muted-foreground shrink-0">
                               {slotLabel}
                             </Label>
                             <div className="flex-1 min-w-0">

app/services/simulations/__tests__/llws-simulator.test.ts

@@ -126,22 +126,48 @@ describe("LLWSSimulator", () => {
       expect(total).toBeCloseTo(1.0, 1);
     });
 
-    it("sum of probFifth across participants equals ~1.0 (4 bracket losers, split evenly)", async () => {
+    it("probFifth sums to ~1.0 (2 Elimination Final losers per sim, split over 5th/6th)", async () => {
       setupMockDb(defaultParticipants(), makeEvRows(ALL_IDS));
       const results = await new LLWSSimulator(1_000).simulate("season-1");
-      // 4 bracket losers per sim, each assigned bracketLoser/(4*N) → sum = 1.0
       const total = results.reduce((s, r) => s + r.probabilities.probFifth, 0);
       expect(total).toBeCloseTo(1.0, 1);
     });
 
-    it("probFifth through probEighth are equal for every participant (even bracket-loser split)", async () => {
+    it("probSeventh sums to ~1.0 (2 Elimination Round 4 losers per sim, split over 7th/8th)", async () => {
+      setupMockDb(defaultParticipants(), makeEvRows(ALL_IDS));
+      const results = await new LLWSSimulator(1_000).simulate("season-1");
+      const total = results.reduce((s, r) => s + r.probabilities.probSeventh, 0);
+      expect(total).toBeCloseTo(1.0, 1);
+    });
+
+    it("ties 5th with 6th and 7th with 8th, but keeps the two tiers separate", async () => {
+      setupMockDb(defaultParticipants(), makeEvRows(ALL_IDS, { includeOdds: true }));
+      const results = await new LLWSSimulator(2_000).simulate("season-1");
+      for (const r of results) {
+        const p = r.probabilities;
+        // Within a tier the two positions are tied.
+        expect(p.probFifth).toBeCloseTo(p.probSixth, 10);
+        expect(p.probSeventh).toBeCloseTo(p.probEighth, 10);
+      }
+      // The tiers are distinct outcomes (losing the Elimination Final vs losing
+      // Elimination Round 4), so they must not be forced equal across the field.
+      const differs = results.some(
+        (r) => Math.abs(r.probabilities.probFifth - r.probabilities.probSeventh) > 1e-9
+      );
+      expect(differs).toBe(true);
+    });
+
+    it("gives every team a total placement probability of at most 1", async () => {
       setupMockDb(defaultParticipants(), makeEvRows(ALL_IDS));
       const results = await new LLWSSimulator(1_000).simulate("season-1");
       for (const r of results) {
         const p = r.probabilities;
-        expect(p.probFifth).toBeCloseTo(p.probSixth, 10);
+        // Each sim assigns a team at most one placement, so summing the distinct
-        expect(p.probSixth).toBeCloseTo(p.probSeventh, 10);
+        // tiers (5th/6th and 7th/8th each count once) cannot exceed 1.
-        expect(p.probSeventh).toBeCloseTo(p.probEighth, 10);
+        const total =
+          p.probFirst + p.probSecond + p.probThird + p.probFourth +
+          p.probFifth * 2 + p.probSeventh * 2;
+        expect(total).toBeLessThanOrEqual(1 + 1e-9);
       }
     });
   });
@@ -179,10 +205,13 @@ describe("LLWSSimulator", () => {
     });
   });
 
-  // ── Pool assignment modes ─────────────────────────────────────────────────
+  // ── Legacy externalId formats ─────────────────────────────────────────────
+  //
+  // The tournament no longer has pool play, but seasons configured for the old
+  // format still carry pool suffixes. Those must keep loading, read as the side alone.
 
-  describe("pool assignment modes", () => {
+  describe("legacy pool-suffix externalIds", () => {
-    it("fixed pools (US:A / US:B / Intl:A / Intl:B) produce valid results", async () => {
+    it("accepts US:A / US:B / Intl:A / Intl:B, ignoring the pool part", async () => {
       setupMockDb(defaultParticipants("fixed"), makeEvRows(ALL_IDS));
       const results = await new LLWSSimulator(1_000).simulate("season-1");
       expect(results).toHaveLength(20);
@@ -190,10 +219,10 @@ describe("LLWSSimulator", () => {
       expect(total).toBeCloseTo(1.0, 1);
     });
 
-    it("mixed mode: US fixed pools, Intl randomized", async () => {
+    it("accepts a mix of suffixed and bare side ids", async () => {
       const participants = [
         ...US_IDS.slice(0, 5).map((id) => ({ id, name: `US Team ${id}`, externalId: "US:A" })),
-        ...US_IDS.slice(5).map((id) => ({ id, name: `US Team ${id}`, externalId: "US:B" })),
+        ...US_IDS.slice(5).map((id) => ({ id, name: `US Team ${id}`, externalId: "US" })),
         ...INTL_IDS.map((id) => ({ id, name: `Team ${id}`, externalId: "Intl" })),
       ];
       setupMockDb(participants, makeEvRows(ALL_IDS));
@@ -202,6 +231,17 @@ describe("LLWSSimulator", () => {
       const total = results.reduce((s, r) => s + r.probabilities.probFirst, 0);
       expect(total).toBeCloseTo(1.0, 1);
     });
+
+    it("accepts an uneven suffix split (pools no longer constrain anything)", async () => {
+      const participants = [
+        ...US_IDS.slice(0, 6).map((id) => ({ id, name: `US Team ${id}`, externalId: "US:A" })),
+        ...US_IDS.slice(6).map((id) => ({ id, name: `US Team ${id}`, externalId: "US:B" })),
+        ...INTL_IDS.map((id) => ({ id, name: `Team ${id}`, externalId: "Intl" })),
+      ];
+      setupMockDb(participants, makeEvRows(ALL_IDS));
+      const results = await new LLWSSimulator(1_000).simulate("season-1");
+      expect(results).toHaveLength(20);
+    });
   });
 
   // ── Error cases ───────────────────────────────────────────────────────────
@@ -262,26 +302,13 @@ describe("LLWSSimulator", () => {
       await expect(new LLWSSimulator(1_000).simulate("season-1")).rejects.toThrow(/10 US teams/);
     });
 
-    it("throws when fixed pools have unequal A/B split", async () => {
+    it("throws when International team count is not 10", async () => {
       const participants = [
-        // 6 in Pool A, 4 in Pool B
+        ...Array.from({ length: 9 }, (_, i) => ({ id: `us-${i + 1}`, name: `US Team ${i + 1}`, externalId: "US" })),
-        ...US_IDS.slice(0, 6).map((id) => ({ id, name: `US Team ${id}`, externalId: "US:A" })),
+        ...Array.from({ length: 11 }, (_, i) => ({ id: `intl-${i + 1}`, name: `Team ${i + 1}`, externalId: "Intl" })),
-        ...US_IDS.slice(6).map((id) => ({ id, name: `US Team ${id}`, externalId: "US:B" })),
-        ...INTL_IDS.map((id) => ({ id, name: `Team ${id}`, externalId: "Intl" })),
       ];
       setupMockDb(participants, makeEvRows(ALL_IDS));
-      await expect(new LLWSSimulator(1_000).simulate("season-1")).rejects.toThrow(/exactly 5 teams each/);
+      await expect(new LLWSSimulator(1_000).simulate("season-1")).rejects.toThrow(/10 US teams/);
-    });
-
-    it("throws when US externalIds mix pool suffixes and bare side", async () => {
-      const participants = [
-        // Some US:A, some "US" (no pool suffix) → mixed
-        ...US_IDS.slice(0, 5).map((id) => ({ id, name: `US Team ${id}`, externalId: "US:A" })),
-        ...US_IDS.slice(5).map((id) => ({ id, name: `US Team ${id}`, externalId: "US" })), // no pool
-        ...INTL_IDS.map((id) => ({ id, name: `Team ${id}`, externalId: "Intl" })),
-      ];
-      setupMockDb(participants, makeEvRows(ALL_IDS));
-      await expect(new LLWSSimulator(1_000).simulate("season-1")).rejects.toThrow(/mixed externalId formats/);
     });
   });
 });

app/services/simulations/llws-simulator.ts

@@ -1,7 +1,13 @@
 /**
  * Little League World Series (LLWS) Bracket Simulator
  *
- * Monte Carlo simulation of the LLWS (20-team format, 2022–present).
+ * Monte Carlo simulation of the LLWS (20-team double-elimination format, 2025+).
+ *
+ * The tournament is two independent 10-team double-elimination brackets — United
+ * States and International — each producing a side champion, then a World
+ * Championship game and a Consolation game between the side runners-up. There is no
+ * pool play. This mirrors the llws_20 bracket template so simulated placements line
+ * up with the bracket admins actually score.
  *
  * Algorithm:
  *   1. Load all 20 participants for the sports season from DB
@@ -10,48 +16,36 @@
  *      (entered via Admin → Futures Odds; American format)
  *   3. Convert odds to normalized championship probabilities (vig removed).
  *      These drive per-game win probability: p1 / (p1 + p2). Falls back to 50/50.
- *   4. Determine pool assignment mode from externalId:
+ *   4. Per simulation:
- *      - Fixed pools: externalId is "US:A", "US:B", "Intl:A", or "Intl:B"
+ *      a. Shuffle each side's 10 teams into the 10 bracket slots (8 opening-round
- *        → use these exact pool assignments every simulation.
+ *         teams + 2 byes). The draw is modelled as random — a specific known draw
- *      - Randomized pools: externalId is "US" or "Intl" only
+ *         is not yet expressible in participant config.
- *        → randomly shuffle each side into Pool A / Pool B each simulation.
+ *      b. Simulate the 10-team double-elimination bracket for each side
- *   5. Per simulation:
+ *         (see simulateSideBracket for the exact game-by-game structure)
- *      a. Assign pools (fixed or random)
+ *      c. Consolation game: US side loser vs Intl side loser → 3rd / 4th
- *      b. Simulate pool play round-robin within each pool (10 games/pool)
+ *      d. World Championship: US champion vs Intl champion → 1st / 2nd
- *         Top 2 by W-L record advance. Ties broken randomly.
+ *   5. Track placement counts across all simulations.
- *      c. Simulate 4-team double-elimination bracket per side:
+ *   6. Convert counts to probability distributions.
- *           G1: A1 vs B2  (WB)
- *           G2: B1 vs A2  (WB)
- *           G3: G1W vs G2W  (WB Final)
- *           G4: G1L vs G2L  (LB R1 — loser eliminated)
- *           G5: G3L vs G4W  (LB Final — loser eliminated)
- *           G6: G3W vs G5W  (Side Championship — loser eliminated)
- *      d. Consolation game: US loser vs Intl loser → 3rd / 4th
- *      e. World Series: US champion vs Intl champion → 1st / 2nd
- *   6. Track placement counts across all simulations.
- *   7. Convert counts to probability distributions.
  *
- * Pool assignment (externalId format):
+ * Side assignment (externalId): "US" or "Intl". The legacy pool suffixes
- *   "US:A" / "US:B" / "Intl:A" / "Intl:B" → fixed pools (post-draw mode)
+ * ("US:A", "US:B", "Intl:A", "Intl:B") are still accepted and read as the side
- *   "US" / "Intl"                           → randomized pools (pre-draw mode)
+ * alone, so seasons configured for the old pool-play format keep working — pools
- *   Mixed: if ANY US or Intl team has a pool suffix, ALL teams on that side must
+ * no longer exist, so the suffix has no effect.
- *   have one (throws otherwise). Sides can differ — US fixed while Intl randomized.
  *
- * Placement tiers → SimulationProbabilities mapping:
+ * Placement tiers → SimulationProbabilities mapping (matches llws_20's scoring):
- *   probFirst              = World Series Champion (1 per sim)
+ *   probFirst            = World Championship winner   (1 per sim)
- *   probSecond             = World Series Runner-up (1 per sim)
+ *   probSecond           = World Championship loser    (1 per sim)
- *   probThird              = Consolation game winner / 3rd place (1 per sim)
+ *   probThird            = Consolation winner          (1 per sim)
- *   probFourth             = Consolation game loser / 4th place (1 per sim)
+ *   probFourth           = Consolation loser           (1 per sim)
- *   probFifth–probEighth   = Double-elim bracket losers before side championships
+ *   probFifth/probSixth  = Elimination Final losers    (2 per sim — 1 per side)
- *                            (4 per sim — split evenly: 2 US + 2 Intl)
+ *   probSeventh/probEighth = Elimination Round 4 losers (2 per sim — 1 per side)
- *   Pool play losers       → all 0 (12 teams, did not advance from pool play)
+ *   Everyone else        → all 0 (12 teams out in Elimination Rounds 1–3)
  *
  * Admin setup:
  *   1. Create a Sport with simulatorType = "llws_bracket"
  *   2. Create a Sports Season and add exactly 20 participants (10 US, 10 International)
- *   3. Set externalId on each participant via Admin → Manage Participants (optional if names follow the convention):
+ *   3. Set externalId on each participant via Admin → Manage Participants to "US" or
- *      Pre-draw:  "US" or "Intl"  (or leave null — names starting with "US " infer US, all others infer Intl)
+ *      "Intl" (optional — names starting with "US " infer US, all others infer Intl)
- *      Post-draw: "US:A", "US:B", "Intl:A", or "Intl:B"
  *   4. Enter championship futures odds via Admin → Futures Odds (sourceOdds)
  *   5. Run simulation via Admin → Simulate
  */
@@ -68,7 +62,6 @@ import { positiveConfigNumber } from "./config-access";
 const NUM_SIMULATIONS = 50_000;
 const US_TEAM_COUNT = 10;
 const INTL_TEAM_COUNT = 10;
-const POOL_SIZE = 5; // teams per pool within each side
 
 // ─── Types ────────────────────────────────────────────────────────────────────
 
@@ -77,8 +70,6 @@ type Side = "US" | "Intl";
 interface Team {
   participantId: string;
   side: Side;
-  /** Explicit pool ("A" or "B") if set in externalId; null if randomized. */
-  fixedPool: "A" | "B" | null;
   /** Normalized championship win probability (0–1, vig removed). */
   oddsProb: number;
 }
@@ -88,11 +79,21 @@ interface PlacementCounts {
   finalist: number;
   thirdPlace: number;
   fourthPlace: number;
-  bracketLoser: number;
+  /** Lost the Elimination Final — the 5th–6th tier (1 per side per sim). */
+  elimFinalLoser: number;
+  /** Lost Elimination Round 4 — the 7th–8th tier (1 per side per sim). */
+  elimRound4Loser: number;
 }
 
 // ─── Helpers ─────────────────────────────────────────────────────────────────
 
+function zeroCounts(): PlacementCounts {
+  return {
+    champion: 0, finalist: 0, thirdPlace: 0, fourthPlace: 0,
+    elimFinalLoser: 0, elimRound4Loser: 0,
+  };
+}
+
 function simGame(t1: Team, t2: Team): { winner: Team; loser: Team } {
   // If either team has no odds entered, treat the game as a coin flip.
   // The 50/50 fallback must cover the one-sided case (one team known, one not)
@@ -118,101 +119,89 @@ function shuffle<T>(arr: T[]): T[] {
 }
 
 /**
- * Assign teams to Pool A / Pool B for one side.
+ * Simulate one side's 10-team double-elimination bracket.
- * In fixed mode, respects the pre-set pool. In randomized mode, shuffles then splits.
- */
-function assignPools(teams: Team[], randomized: boolean): [Team[], Team[]] {
-  if (!randomized) {
-    return [teams.filter((t) => t.fixedPool === "A"), teams.filter((t) => t.fixedPool === "B")];
-  }
-  const shuffled = shuffle([...teams]);
-  return [shuffled.slice(0, 5), shuffled.slice(5)];
-}
-
-/**
- * Simulate round-robin pool play among 5 teams.
- * Returns the top 2 teams by win count (ties broken randomly).
- */
-function simulatePoolPlay(pool: Team[]): [Team, Team] {
-  const wins = new Map<string, number>(pool.map((t) => [t.participantId, 0]));
-
-  // Each pair plays once.
-  for (let i = 0; i < pool.length; i++) {
-    for (let j = i + 1; j < pool.length; j++) {
-      const { winner } = simGame(pool[i], pool[j]);
-      wins.set(winner.participantId, (wins.get(winner.participantId) ?? 0) + 1);
-    }
-  }
-
-  // Sort by wins descending; pre-generate a stable random tiebreaker per team so
-  // the comparator is consistent (Math.random() inside a comparator is a bug — the
-  // engine may call it multiple times per pair and get contradictory results).
-  const tiebreaker = new Map(pool.map((t) => [t.participantId, Math.random()]));
-  const ranked = pool.toSorted((a, b) => {
-    const diff = (wins.get(b.participantId) ?? 0) - (wins.get(a.participantId) ?? 0);
-    return diff !== 0 ? diff : (tiebreaker.get(a.participantId) ?? 0) - (tiebreaker.get(b.participantId) ?? 0);
-  });
-
-  return [ranked[0], ranked[1]];
-}
-
-/**
- * Simulate a 4-team double-elimination bracket for one side.
  *
- * Seeds (pool results):
+ * `slots` holds the side's teams in bracket order, matching the llws_20 participant
- *   poolA1 = Pool A winner, poolA2 = Pool A runner-up
+ * layout: slots[0..7] are the four opening-round games (two teams each) and
- *   poolB1 = Pool B winner, poolB2 = Pool B runner-up
+ * slots[8], slots[9] are the two bye teams entering Winners Round 2.
  *
- * Bracket:
+ * Structure (side-local, mirroring LLWS_ADVANCEMENT in models/playoff-match):
- *   G1 (WB): A1 vs B2
+ *   Winners bracket
- *   G2 (WB): B1 vs A2
+ *     OP1 s0 v s1   OP2 s2 v s3   OP3 s4 v s5   OP4 s6 v s7
- *   G3 (WB Final): G1W vs G2W
+ *     WR2-1 s8 v OP1w            WR2-2 s9 v OP2w
- *   G4 (LB R1):    G1L vs G2L  → loser eliminated (bracketLoser)
+ *     WSF1 OP3w v WR2-1w         WSF2 WR2-2w v OP4w
- *   G5 (LB Final): G3L vs G4W  → loser eliminated (bracketLoser)
+ *     WF   WSF1w v WSF2w         → winner to the side championship
- *   G6 (Side Championship): G3W vs G5W → loser eliminated (sideLoser)
+ *   Elimination bracket (a loss here is final)
+ *     ER1-1 OP2l v OP3l          ER1-2 OP1l v OP4l
+ *     ER2-1 WR2-1l v ER1-1w      ER2-2 WR2-2l v ER1-2w
+ *     ER3-1 WSF1l v ER2-2w       ER3-2 WSF2l v ER2-1w   (cross-over)
+ *     ER4   ER3-2w v ER3-1w      → loser is the 7th–8th tier
+ *     EF    WFl v ER4w           → loser is the 5th–6th tier
+ *   Side championship: WFw v EFw → loser drops to the consolation game
  *
- * Returns: { sideChampion, sideLoser }
+ * Note the double-chance path: the Winners Final loser is NOT out, it drops to the
- *   bracketLosers (2) are bumped into counts directly.
+ * Elimination Final. There is no "if necessary" game, so the side championship is
+ * decided in one game.
+ *
+ * Returns { sideChampion, sideLoser }; the two scoring elimination losers are
+ * bumped into the counts directly.
  */
 function simulateSideBracket(
-  poolA1: Team,
+  slots: Team[],
-  poolA2: Team,
-  poolB1: Team,
-  poolB2: Team,
   bump: (id: string, key: keyof PlacementCounts) => void
 ): { sideChampion: Team; sideLoser: Team } {
+  // ── Winners bracket ────────────────────────────────────────────────────────
+  const op1 = simGame(slots[0], slots[1]);
+  const op2 = simGame(slots[2], slots[3]);
+  const op3 = simGame(slots[4], slots[5]);
+  const op4 = simGame(slots[6], slots[7]);
 
-  // Winners bracket
+  const wr21 = simGame(slots[8], op1.winner);
-  const g1 = simGame(poolA1, poolB2);
+  const wr22 = simGame(slots[9], op2.winner);
-  const g2 = simGame(poolB1, poolA2);
-  const g3 = simGame(g1.winner, g2.winner); // WB Final
 
-  // Losers bracket
+  const wsf1 = simGame(op3.winner, wr21.winner);
-  const g4 = simGame(g1.loser, g2.loser);   // LB R1 — g4.loser eliminated
+  const wsf2 = simGame(wr22.winner, op4.winner);
-  bump(g4.loser.participantId, "bracketLoser");
 
-  const g5 = simGame(g3.loser, g4.winner);   // LB Final — g5.loser eliminated
+  const wf = simGame(wsf1.winner, wsf2.winner);
-  bump(g5.loser.participantId, "bracketLoser");
 
-  // Side championship
+  // ── Elimination bracket ────────────────────────────────────────────────────
-  const g6 = simGame(g3.winner, g5.winner);
+  const er11 = simGame(op2.loser, op3.loser);
+  const er12 = simGame(op1.loser, op4.loser);
 
-  return { sideChampion: g6.winner, sideLoser: g6.loser };
+  const er21 = simGame(wr21.loser, er11.winner);
+  const er22 = simGame(wr22.loser, er12.winner);
+
+  // Cross-over: each semifinal loser meets the winner from the opposite half.
+  const er31 = simGame(wsf1.loser, er22.winner);
+  const er32 = simGame(wsf2.loser, er21.winner);
+
+  const er4 = simGame(er32.winner, er31.winner);
+  bump(er4.loser.participantId, "elimRound4Loser"); // 7th–8th tier
+
+  // The Winners Final loser gets its second chance here.
+  const ef = simGame(wf.loser, er4.winner);
+  bump(ef.loser.participantId, "elimFinalLoser"); // 5th–6th tier
+
+  // ── Side championship ──────────────────────────────────────────────────────
+  const sideChampionship = simGame(wf.winner, ef.winner);
+
+  return { sideChampion: sideChampionship.winner, sideLoser: sideChampionship.loser };
 }
 
 // ─── Validation helpers ───────────────────────────────────────────────────────
 
-type PoolSuffix = "A" | "B" | null;
+/**
-
+ * Parse a participant's externalId into a side.
-function parseExternalId(raw: string | null): { side: Side; pool: PoolSuffix } | null {
+ *
+ * The legacy pool-play suffixes ("US:A", "Intl:B", …) are still accepted so seasons
+ * configured before the format change keep loading; the pool part is ignored because
+ * the tournament no longer has pools.
+ */
+function parseExternalId(raw: string | null): { side: Side } | null {
   if (!raw) return null;
-  const upper = raw.toUpperCase();
+  const side = raw.toUpperCase().split(":")[0];
-  if (upper === "US") return { side: "US", pool: null };
+  if (side === "US") return { side: "US" };
-  if (upper === "INTL") return { side: "Intl", pool: null };
+  if (side === "INTL") return { side: "Intl" };
-  if (upper === "US:A") return { side: "US", pool: "A" };
-  if (upper === "US:B") return { side: "US", pool: "B" };
-  if (upper === "INTL:A") return { side: "Intl", pool: "A" };
-  if (upper === "INTL:B") return { side: "Intl", pool: "B" };
   return null;
 }
 
@@ -227,36 +216,6 @@ function inferExternalIdFromName(name: string): string {
   return upper === "US" || upper.startsWith("US ") ? "US" : "Intl";
 }
 
-/**
- * Determine whether pool assignments should be randomized for one side.
- * - If ALL teams on the side have a pool suffix → fixed pools (returns false).
- * - If NO teams have a pool suffix → randomized (returns true).
- * - Mixed → throws.
- * Also validates that fixed pools are split exactly POOL_SIZE / POOL_SIZE.
- */
-function determineRandomized(sideTeams: Team[], sideName: string): boolean {
-  const withPool = sideTeams.filter((t) => t.fixedPool !== null);
-  const withoutPool = sideTeams.filter((t) => t.fixedPool === null);
-  if (withPool.length > 0 && withoutPool.length > 0) {
-    throw new Error(
-      `${sideName} teams have mixed externalId formats: some have pool suffixes (e.g. "US:A") ` +
-      `and some don't. Either all ${sideName} teams must have pool suffixes or none should.`
-    );
-  }
-  if (withPool.length === sideTeams.length) {
-    const poolA = sideTeams.filter((t) => t.fixedPool === "A");
-    const poolB = sideTeams.filter((t) => t.fixedPool === "B");
-    if (poolA.length !== POOL_SIZE || poolB.length !== POOL_SIZE) {
-      throw new Error(
-        `${sideName} fixed pools must have exactly ${POOL_SIZE} teams each. ` +
-        `Found Pool A: ${poolA.length}, Pool B: ${poolB.length}.`
-      );
-    }
-    return false; // fixed pools
-  }
-  return true; // randomized
-}
-
 // ─── Simulator ────────────────────────────────────────────────────────────────
 
 export class LLWSSimulator implements Simulator {
@@ -304,7 +263,7 @@ export class LLWSSimulator implements Simulator {
       }
     }
 
-    // 4. Parse externalId for each participant to determine side and fixed pool.
+    // 4. Parse externalId for each participant to determine which side they're on.
     const teams: Team[] = [];
     for (const p of participants) {
       const raw = p.externalId ?? inferExternalIdFromName(p.name);
@@ -312,13 +271,12 @@ export class LLWSSimulator implements Simulator {
       if (!parsed) {
         throw new Error(
           `Participant ${p.id} has invalid externalId "${p.externalId}". ` +
-          `Expected: "US", "Intl", "US:A", "US:B", "Intl:A", or "Intl:B".`
+          `Expected: "US" or "Intl".`
         );
       }
       teams.push({
         participantId: p.id,
         side: parsed.side,
-        fixedPool: parsed.pool,
         oddsProb: normalizedOddsMap.get(p.id) ?? 0,
       });
     }
@@ -334,15 +292,9 @@ export class LLWSSimulator implements Simulator {
       throw new Error(`Expected ${INTL_TEAM_COUNT} International teams, found ${intlTeams.length}.`);
     }
 
-    // Determine pool assignment mode for each side.
-    const usRandomized = determineRandomized(usTeams, "US");
-    const intlRandomized = determineRandomized(intlTeams, "International");
-
     // 5. Initialise placement count accumulators for all participants.
     const allIds = participants.map((p) => p.id);
-    const counts = new Map<string, PlacementCounts>(
+    const counts = new Map<string, PlacementCounts>(allIds.map((id) => [id, zeroCounts()]));
-      allIds.map((id) => [id, { champion: 0, finalist: 0, thirdPlace: 0, fourthPlace: 0, bracketLoser: 0 }])
-    );
     const bump = (id: string, key: keyof PlacementCounts) => {
       const entry = counts.get(id);
       if (entry) entry[key]++;
@@ -350,42 +302,35 @@ export class LLWSSimulator implements Simulator {
 
     // 6. Run Monte Carlo simulations.
     for (let s = 0; s < numSimulations; s++) {
-      // Assign pools for this simulation.
+      // The draw is modelled as random: shuffle each side into the 10 bracket slots
-      const [usPoolA, usPoolB] = assignPools(usTeams, usRandomized);
+      // (8 opening-round teams, then the 2 bye teams).
-      const [intlPoolA, intlPoolB] = assignPools(intlTeams, intlRandomized);
-
-      // Pool play: top 2 from each pool advance.
-      const [usA1, usA2] = simulatePoolPlay(usPoolA);
-      const [usB1, usB2] = simulatePoolPlay(usPoolB);
-      const [intlA1, intlA2] = simulatePoolPlay(intlPoolA);
-      const [intlB1, intlB2] = simulatePoolPlay(intlPoolB);
-
-      // Double-elimination bracket per side.
       const { sideChampion: usChamp, sideLoser: usLose } =
-        simulateSideBracket(usA1, usA2, usB1, usB2, bump);
+        simulateSideBracket(shuffle([...usTeams]), bump);
       const { sideChampion: intlChamp, sideLoser: intlLose } =
-        simulateSideBracket(intlA1, intlA2, intlB1, intlB2, bump);
+        simulateSideBracket(shuffle([...intlTeams]), bump);
 
       // Consolation game: 3rd / 4th place.
       const consolation = simGame(usLose, intlLose);
       bump(consolation.winner.participantId, "thirdPlace");
       bump(consolation.loser.participantId, "fourthPlace");
 
-      // World Series: 1st / 2nd place.
+      // World Championship: 1st / 2nd place.
       const ws = simGame(usChamp, intlChamp);
       bump(ws.winner.participantId, "champion");
       bump(ws.loser.participantId, "finalist");
     }
 
     // 7. Convert counts to probability distributions.
-    //    bracketLosers: 4 per sim (2 US + 2 Intl) → split evenly.
+    //    Each of the two 5–8 tiers takes exactly 2 teams per sim (one per side), and
-    const bracketLosersPerSim = 4;
+    //    the teams within a tier are tied, so the tier probability is split across
-    const bracketDivisor = bracketLosersPerSim * numSimulations;
+    //    its two positions.
+    const tierDivisor = 2 * numSimulations;
 
-    const zeroCounts: PlacementCounts = { champion: 0, finalist: 0, thirdPlace: 0, fourthPlace: 0, bracketLoser: 0 };
+    const empty = zeroCounts();
     return allIds.map((id) => {
-      const c = counts.get(id) ?? zeroCounts;
+      const c = counts.get(id) ?? empty;
-      const bracketProb = c.bracketLoser / bracketDivisor;
+      const upperTier = c.elimFinalLoser / tierDivisor;   // 5th–6th
+      const lowerTier = c.elimRound4Loser / tierDivisor;  // 7th–8th
       return {
         participantId: id,
         probabilities: {
@@ -393,10 +338,10 @@ export class LLWSSimulator implements Simulator {
           probSecond: c.finalist / numSimulations,
           probThird: c.thirdPlace / numSimulations,
           probFourth: c.fourthPlace / numSimulations,
-          probFifth: bracketProb,
+          probFifth: upperTier,
-          probSixth: bracketProb,
+          probSixth: upperTier,
-          probSeventh: bracketProb,
+          probSeventh: lowerTier,
-          probEighth: bracketProb,
+          probEighth: lowerTier,
         },
         source: "llws_monte_carlo",
       };

app/services/simulations/manifest.ts

@@ -183,7 +183,7 @@ const PROFILES: Record<SimulatorType, Omit<SimulatorManifestProfile, "simulatorT
     setupSections: ["participants", "eloRatings", "futuresOdds", "bracket"],
   },
   llws_bracket: {
-    defaultConfig: { ...BASE_CONFIG, usTeamCount: 10, internationalTeamCount: 10, poolSize: 5 },
+    defaultConfig: { ...BASE_CONFIG, usTeamCount: 10, internationalTeamCount: 10 },
     requiredInputs: ["sourceOdds"],
     optionalInputs: ["metadata"],
     setupSections: ["participants", "futuresOdds"],

app/services/simulations/registry.ts

@@ -168,7 +168,7 @@ const REGISTRY: Record<SimulatorType, { info: SimulatorInfo; create: () => Simul
   llws_bracket: {
     info: {
       name: "LLWS Bracket Monte Carlo",
-      description: "Simulates the 20-team Little League World Series: pool play round-robin (5 teams/pool, top 2 advance) → 4-team double-elimination bracket per side (US & International) → consolation game (3rd/4th) → World Series. Uses championship futures odds for all win probabilities. Set externalId to 'US'/'Intl' (randomized pools) or 'US:A'/'US:B'/'Intl:A'/'Intl:B' (fixed pools).",
+      description: "Simulates the 20-team Little League World Series: a 10-team double-elimination bracket per side (US & International), each producing a side champion, then the consolation game (3rd/4th) and the World Championship (1st/2nd). Uses championship futures odds for all win probabilities. Set externalId to 'US' or 'Intl'.",
     },
     create: () => new LLWSSimulator(),
   },