P3.2: cascade combo multiplier (pure sx)

Scale each cascade round's base points by combo_multiplier(round) = the
1-based round index (round 1 x1, round 2 x2, ...), so deeper chains pay
out more. resolve now reads score_round before each clear, accumulates
score_round * combo_multiplier(round) into Board.score, and reports the
settle's payout as the new Cascade.awarded field. A depth-1 settle scores
exactly its base (x1, no bonus); any multi-round chain strictly exceeds
the same clears scored flat.

resolve_step keeps its signature (no scoring), so cascade.sx and its
golden are unchanged; score_round/add_round_score are untouched, so
score.sx is unchanged. New tests/combo.sx golden locks exact cumulative
scores for a single-round clear (30), the P2.4 cascade board (flat 60 ->
mult 90), and a controlled 3-round chain (flat 90 -> mult 180), printing
per-round base/multiplier/points so the golden self-explains.

board.sx

@@ -88,10 +88,10 @@ Board :: struct {
     // must seed this before any draw.
     rng: Rng;
 
-    // Running score total (P3.1). `init` zeroes it; `add_round_score` accumulates
-    // a round's base points (see `score_round`). The cascade-wide combo MULTIPLIER
-    // off `Cascade.depth` lands in P3.2, and the HUD (P4.4) reads this field. A
-    // hand-built board must zero this before accumulating.
+    // Running score total. `init` zeroes it; `add_round_score` adds a single
+    // round's base points (see `score_round`), and `resolve` adds each cascade
+    // round's base scaled by `combo_multiplier` (P3.2). The HUD (P4.4) reads this
+    // field. A hand-built board must zero this before accumulating.
     score: s64;
 
     idx :: (col: s64, row: s64) -> s64 {
@@ -474,11 +474,14 @@ refill :: (board: *Board) -> s64 {
 // Outcome of resolving a board to a stable state. `depth` is the number of
 // rounds that found and cleared at least one match (0 for an already-stable
 // board). `cleared` holds those rounds' cleared-cell counts in round order, so
-// `cleared.len == depth`; P3 scores each round off this list and reads the
-// combo multiplier from the depth.
+// `cleared.len == depth`. `awarded` is the total points this settle added to
+// `Board.score`: the sum over rounds of `score_round * combo_multiplier(round)`
+// (P3.2), so the HUD (P4.4) and turn accounting (P3.3) can read a swap's payout
+// without re-deriving it. A depth-0 (already-stable) board awards 0.
 Cascade :: struct {
     depth: s64;
     cleared: List(s64);
+    awarded: s64;
 }
 
 // One resolution round: detect matches and, if any, clear them, collapse under
@@ -494,16 +497,24 @@ resolve_step :: (board: *Board) -> s64 {
     cleared
 }
 
-// Resolve the board to a stable state, running rounds until one finds no match.
-// Returns the cascade: its depth and per-round cleared-cell counts. An
-// already-stable board returns depth 0 with an empty `cleared` list, untouched.
+// Resolve the board to a stable state, running rounds until one finds no match,
+// scoring each round with the cascade combo multiplier (P3.2). Returns the
+// cascade: its depth, per-round cleared-cell counts, and total `awarded` points.
+// Each round adds `score_round * combo_multiplier(round)` (round 1-based) to
+// `Board.score`; an already-stable board returns depth 0, awards 0, untouched.
 resolve :: (board: *Board) -> Cascade {
-    result := Cascade.{ depth = 0, cleared = List(s64).{} };
+    result := Cascade.{ depth = 0, cleared = List(s64).{}, awarded = 0 };
     while true {
+        // Read the round's base points while its runs are still on the board:
+        // `resolve_step` clears them, so the score has to be taken first.
+        base := score_round(board);
         n := resolve_step(board);
         if n == 0 { break; }
-        result.cleared.append(n);
         result.depth += 1;
+        points := base * combo_multiplier(result.depth);
+        board.score += points;
+        result.awarded += points;
+        result.cleared.append(n);
     }
     result
 }
@@ -521,7 +532,8 @@ resolve :: (board: *Board) -> Cascade {
 // corner) scores horizontal + vertical — the corner counts toward both runs'
 // lengths, unlike the cleared-cell set which unions it once.
 //
-// One round only: the cross-round combo MULTIPLIER (off `Cascade.depth`) is P3.2.
+// One round only: the cross-round combo MULTIPLIER is `combo_multiplier` (P3.2),
+// applied by `resolve`; this base scheme is unscaled.
 SCORE_RUN_3      :: 30;
 SCORE_RUN_4      :: 60;
 SCORE_RUN_5_PLUS :: 100;
@@ -602,16 +614,29 @@ score_round :: (board: *Board) -> s64 {
     total
 }
 
-// Add this round's base points to the board's running `score` total and return
-// them. The accumulation primitive the HUD (P4.4) reads and that P3.2 wraps with
-// the cascade combo multiplier — P3.2 layers the per-round multiplier here / in
-// the resolve loop without changing `score_round`.
+// Add this round's base points (×1, no combo multiplier) to the board's running
+// `score` total and return them. The single-round accumulation primitive; the
+// cascade loop (`resolve`) instead scales each round by `combo_multiplier`
+// (P3.2). Neither path changes `score_round`.
 add_round_score :: (board: *Board) -> s64 {
     points := score_round(board);
     board.score += points;
     points
 }
 
+// ── Combo multiplier (P3.2) ────────────────────────────────────────────────
+// Across one swap's cascade, each resolution round's base points (`score_round`)
+// are scaled by a multiplier that grows with chain depth, so deeper chains pay
+// out more. The scheme: the 1-based round index IS the multiplier — round 1 ×1,
+// round 2 ×2, round 3 ×3, … A single-round settle (depth 1) therefore scores
+// exactly its base (×1, no bonus); every round past the first is amplified, so a
+// multi-round chain strictly beats the same clears scored flat. `resolve`
+// accumulates `score_round * combo_multiplier(round)` per round into `Board.score`
+// and reports the sum as `Cascade.awarded`.
+combo_multiplier :: (round: s64) -> s64 {
+    round
+}
+
 // Deterministic textual dump of an enumerated run list, in `find_runs` order: a
 // count header, then one run per line as `<axis> len <n> at fixed <f> start <s>`
 // where axis is H (horizontal) or V (vertical). An empty list dumps as just

tests/combo.sx

@@ -0,0 +1,140 @@
+// Combo-multiplier golden (P3.2): drive seeded boards through the full cascade
+// settle and snapshot the per-round scoring. Each round's base points
+// (`score_round`) are scaled by `combo_multiplier(round)` = the 1-based round
+// index, so round 1 ×1, round 2 ×2, round 3 ×3, …; `resolve` accumulates the
+// multiplied sum into `Board.score` and reports it as `Cascade.awarded`.
+//
+// Three scenes prove the rule end to end:
+//   - single-depth1: one clear, depth 1 → base ×1 = base exactly (NO bonus).
+//   - cascade-depth2: the P2.4 cascade board (seed 7) → a real 2-round chain
+//     whose multiplied total (90) strictly beats the flat sum (60).
+//   - chain-depth3: the same crafted board at seed 10 → a 3-round chain,
+//     30×1 + 30×2 + 30×3 = 180, well above the flat 90.
+//
+// For each scene the starting board and every round's (cleared, base, multiplier,
+// round points) are printed so the golden is self-explanatory, the flat and
+// multiplied totals are printed side by side, and `resolve` on a fresh identical
+// board is asserted to award EXACTLY the multiplied total into `Board.score`.
+#import "modules/std.sx";
+#import "board.sx";
+t :: #import "test.sx";
+
+// Inverse of `gem_char`: map a board character back to its Gem so each board can
+// be written as a human-readable grid. The hole glyph maps to `.empty`.
+char_to_gem :: (c: u8) -> Gem {
+    if c == EMPTY_CHAR { return .empty; }
+    for 0..GEM_COUNT: (i) {
+        if GEM_CHARS[i] == c { return cast(Gem) i; }
+    }
+    .red
+}
+
+// Load an 8x8 board from `rows` (top row first, each exactly BOARD_COLS chars),
+// seeded RNG, running score zeroed so `board.score` ends equal to the payout.
+load_board :: (rows: []string, seed: s64) -> Board {
+    b : Board = ---;
+    for 0..BOARD_ROWS: (row) {
+        line := rows[row];
+        for 0..BOARD_COLS: (col) {
+            b.set(col, row, char_to_gem(line[col]));
+        }
+    }
+    b.rng = rng_seeded(seed);
+    b.score = 0;
+    b
+}
+
+// One scene: drive the settle one round at a time so each round is visible in the
+// snapshot — score_round BEFORE the clear, multiplier off the 1-based round index,
+// mirroring `resolve` exactly. Print per-round (cleared, base, multiplier, round
+// points) and the flat-vs-multiplied totals, then assert `resolve` on a fresh
+// identical board awards `want_mult` into `Board.score` and reports it as
+// `Cascade.awarded` at the same depth. A depth-1 settle must equal the flat sum
+// (no bonus); a deeper chain must strictly exceed it.
+scene :: (name: string, rows: []string, seed: s64, want_flat: s64, want_mult: s64) {
+    print("== {} ==\n", name);
+    b := load_board(rows, seed);
+    out(board_dump(@b));
+
+    flat : s64 = 0;
+    mult : s64 = 0;
+    depth : s64 = 0;
+    while true {
+        base := score_round(@b);
+        n := resolve_step(@b);
+        if n == 0 { break; }
+        depth += 1;
+        m := combo_multiplier(depth);
+        print("round {}: cleared {} base {} x{} = {}\n", depth, n, base, m, base * m);
+        flat += base;
+        mult += base * m;
+    }
+    print("flat sum {}\n", flat);
+    print("multiplied total {}\n", mult);
+
+    t.expect(flat == want_flat, concat(name, ": flat sum exact"));
+    t.expect(mult == want_mult, concat(name, ": multiplied total exact"));
+    if depth >= 2 {
+        t.expect(mult > flat, concat(name, ": multi-round chain beats flat sum"));
+    } else {
+        t.expect(mult == flat, concat(name, ": single round scores flat (no bonus)"));
+    }
+
+    // The public `resolve` on a fresh identical board reproduces the payout:
+    // accumulates the multiplied total into `Board.score` and reports it as
+    // `Cascade.awarded`, at the same depth.
+    b2 := load_board(rows, seed);
+    c := resolve(@b2);
+    t.expect(c.depth == depth, concat(name, ": resolve depth matches manual loop"));
+    t.expect(c.awarded == want_mult, concat(name, ": resolve awarded equals multiplied total"));
+    t.expect(b2.score == want_mult, concat(name, ": resolve accumulates into board.score"));
+}
+
+main :: () -> s32 {
+    print("== combo (cascade multiplier) ==\n");
+
+    // Single-round clear (seed 0): one RRR clears and the refill makes no new
+    // match, so the settle stops at depth 1 → base 30 ×1 = 30, exactly the flat
+    // value. Proves there is no combo bonus on a single round.
+    scene("single-depth1", .[
+        "RRRGOGOG",
+        "GOGOGOGO",
+        "OGOGOGOG",
+        "GOGOGOGO",
+        "OGOGOGOG",
+        "GOGOGOGO",
+        "OGOGOGOG",
+        "GOGOGOGO",
+    ], 0, 30, 30);
+
+    // The P2.4 cascade board (seed 7): round 1 clears the horizontal BBB (base 30
+    // ×1), round 2 the gravity-formed vertical RRR (base 30 ×2) → 30 + 60 = 90,
+    // strictly above the flat 30 + 30 = 60.
+    scene("cascade-depth2", .[
+        "OGOGOGOG",
+        "GOGOGOGO",
+        "RGOGOGOG",
+        "BBBOGOGO",
+        "RGOGOGOG",
+        "ROGOGOGO",
+        "OGOGOGOG",
+        "GOGOGOGO",
+    ], 7, 60, 90);
+
+    // The same crafted board at seed 10: the refill after round 2 sets up a third
+    // len-3 clear, a controlled 3-round chain → 30×1 + 30×2 + 30×3 = 180, well
+    // above the flat 90.
+    scene("chain-depth3", .[
+        "OGOGOGOG",
+        "GOGOGOGO",
+        "RGOGOGOG",
+        "BBBOGOGO",
+        "RGOGOGOG",
+        "ROGOGOGO",
+        "OGOGOGOG",
+        "GOGOGOGO",
+    ], 10, 90, 180);
+
+    print("ok: combo multiplier scales cascade rounds\n");
+    return 0;
+}

tests/expected/combo.exit

@@ -0,0 +1 @@
+0

tests/expected/combo.stdout

@@ -0,0 +1,41 @@
+== combo (cascade multiplier) ==
+== single-depth1 ==
+RRRGOGOG
+GOGOGOGO
+OGOGOGOG
+GOGOGOGO
+OGOGOGOG
+GOGOGOGO
+OGOGOGOG
+GOGOGOGO
+round 1: cleared 3 base 30 x1 = 30
+flat sum 30
+multiplied total 30
+== cascade-depth2 ==
+OGOGOGOG
+GOGOGOGO
+RGOGOGOG
+BBBOGOGO
+RGOGOGOG
+ROGOGOGO
+OGOGOGOG
+GOGOGOGO
+round 1: cleared 3 base 30 x1 = 30
+round 2: cleared 3 base 30 x2 = 60
+flat sum 60
+multiplied total 90
+== chain-depth3 ==
+OGOGOGOG
+GOGOGOGO
+RGOGOGOG
+BBBOGOGO
+RGOGOGOG
+ROGOGOGO
+OGOGOGOG
+GOGOGOGO
+round 1: cleared 3 base 30 x1 = 30
+round 2: cleared 3 base 30 x2 = 60
+round 3: cleared 3 base 30 x3 = 90
+flat sum 90
+multiplied total 180
+ok: combo multiplier scales cascade rounds