Phase 1: smarter auto-layout (best-fit, plywood rotation, optimize)

- Lumber packing supports first-fit (FFD) and best-fit (BFD, tightest fit) via
  a `fit` mode; strategy "bestfit" selects it.
- Plywood panels now rotate to fit (when allowed and grain isn't honored);
  placements record `rotated`. Rotation-disabled oversize panels are flagged.
- best_cut_plan() tries decreasing/bestfit/increasing + shuffle restarts and
  keeps the best by (stock_count, waste_area, -reusable_offcuts); marks it
  "optimized". STRATEGIES drives "Try alternative".
- BOM Cut Layout tab: "Find better layout" (optimize) + "Try alternative"
  (cycle strategies) buttons; the score line explains the result.

107 tests pass (rotation fits/!fits, optimizer no-worse-than-baseline).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/woodshop/cutplan.py

@@ -144,25 +144,32 @@ def _ordered(items, strategy):
     key = lambda it: max(it.length_in, it.width_in)
     if strategy == "increasing":
         return sorted(items, key=key)
-    if strategy == "shuffle":
+    if strategy.startswith("shuffle"):           # "shuffle", "shuffle1", ... distinct salts
-        return sorted(items, key=lambda it: (hash(it.id) & 0xffff))
+        salt = strategy[7:]
-    return sorted(items, key=key, reverse=True)
+        return sorted(items, key=lambda it: (hash(it.id + salt) & 0xffffff))
+    return sorted(items, key=key, reverse=True)   # decreasing (FFD) & bestfit (BFD)
 
 
-def _pack_lumber(items, stock, s: ShopSettings, ids) -> tuple[list, list]:
+def _lumber_avail(sp, s):
-    """First-fit-decreasing into sticks. Returns (stock_pieces, unplaced_ids)."""
+    end = max((p.x_in + p.len_in for p in sp.placements), default=0.0)
+    cursor = end + (s.kerf_in if sp.placements else 0.0)
+    return sp.length_in - cursor, cursor       # (room left, x where the next piece starts)
+
+
+def _pack_lumber(items, stock, s: ShopSettings, ids, fit="first") -> tuple[list, list]:
+    """Pack lengths into sticks. fit='first' (FFD) or 'best' (BFD = tightest fit)."""
     sticks, unplaced = [], []
     for it in items:
         if it.length_in > s.stick_len_in + _EPS:
             unplaced.append(it.id)
             continue
-        for sp in sticks:
+        candidates = [(sp,) + _lumber_avail(sp, s) for sp in sticks]
-            end = max((p.x_in + p.len_in for p in sp.placements), default=0.0)
+        candidates = [(sp, room, x) for sp, room, x in candidates if it.length_in <= room + _EPS]
-            cursor = end + (s.kerf_in if sp.placements else 0.0)
+        if candidates:
-            if cursor + it.length_in <= s.stick_len_in + _EPS:
+            sp, _room, x = (min(candidates, key=lambda c: c[1]) if fit == "best"
-                sp.placements.append(Placement(id=ids(), item_id=it.id, x_in=cursor,
+                            else candidates[0])
+            sp.placements.append(Placement(id=ids(), item_id=it.id, x_in=x,
                                            len_in=it.length_in, wid_in=it.width_in))
-                break
         else:
             sp = StockPiece(id=ids("sp"), stock=stock, is_sheet=False,
                             length_in=s.stick_len_in, width_in=it.width_in)
@@ -183,27 +190,39 @@ def _pack_plywood(items, stock, s: ShopSettings, ids) -> tuple[list, list]:
     sheets, rest = [], list(items)
     unplaced = []
 
+    def orientations(it):
+        # (len_along_sheet, width_across, rotated). Rotation allowed unless grain is honored.
+        opts = [(it.length_in, it.width_in, False)]
+        if s.allow_plywood_rotation and not s.grain_direction and it.width_in != it.length_in:
+            opts.append((it.width_in, it.length_in, True))
+        return opts
+
     def pack_one(panels):
         sp = StockPiece(id=ids("sp"), stock=stock, is_sheet=True,
                         length_in=s.sheet_l_in, width_in=s.sheet_w_in)
         shelves, leftover = [], []          # shelves: [y, height, x_cursor]
         for it in panels:
             done = False
-            for sh in shelves:
+            for pl, pw, rot in orientations(it):
+                for sh in shelves:          # fit into an existing shelf
                     x = sh[2] + (s.kerf_in if sh[2] else 0.0)
-                if it.width_in <= sh[1] + _EPS and x + it.length_in <= s.sheet_l_in + _EPS:
+                    if pw <= sh[1] + _EPS and x + pl <= s.sheet_l_in + _EPS:
                         sp.placements.append(Placement(id=ids(), item_id=it.id, x_in=x, y_in=sh[0],
-                                                   len_in=it.length_in, wid_in=it.width_in))
+                                                       len_in=pl, wid_in=pw, rotated=rot))
-                    sh[2] = x + it.length_in
+                        sh[2] = x + pl
                         done = True
                         break
+                if done:
+                    break
             if not done:
+                for pl, pw, rot in orientations(it):   # start a new shelf
                     y = (shelves[-1][0] + shelves[-1][1] + s.kerf_in) if shelves else 0.0
-                if y + it.width_in <= s.sheet_w_in + _EPS and it.length_in <= s.sheet_l_in + _EPS:
+                    if y + pw <= s.sheet_w_in + _EPS and pl <= s.sheet_l_in + _EPS:
-                    shelves.append([y, it.width_in, it.length_in])
+                        shelves.append([y, pw, pl])
                         sp.placements.append(Placement(id=ids(), item_id=it.id, x_in=0.0, y_in=y,
-                                                   len_in=it.length_in, wid_in=it.width_in))
+                                                       len_in=pl, wid_in=pw, rotated=rot))
                         done = True
+                        break
             if not done:
                 leftover.append(it)
         return sp, leftover
@@ -230,6 +249,7 @@ def build_cut_plan(scene, settings: ShopSettings | None = None,
         counter["n"] += 1
         return f"{prefix}{counter['n']}"
 
+    fit = "best" if strategy == "bestfit" else "first"
     by_stock: dict[str, list] = {}
     for it in _ordered(items, strategy):
         by_stock.setdefault(it.stock, []).append(it)
@@ -239,7 +259,7 @@ def build_cut_plan(scene, settings: ShopSettings | None = None,
         if its[0].is_sheet:
             sps, un = _pack_plywood(its, stock, s, ids)
         else:
-            sps, un = _pack_lumber(its, stock, s, ids)
+            sps, un = _pack_lumber(its, stock, s, ids, fit=fit)
         stock_pieces += sps
         unplaced += un
     for item_id in unplaced:
@@ -278,6 +298,32 @@ def _score(stock_pieces, s, strategy, warnings) -> dict:
     }
 
 
+def _plan_key(plan: CutPlan):
+    """Lower is better: fewest stock pieces, then least waste, then more reusable offcuts."""
+    sc = plan.score
+    return (sc["stock_count"], sc["waste_area"], -sc["reusable_offcuts"])
+
+
+# Strategies the "Try alternative" button cycles through.
+STRATEGIES = ["decreasing", "bestfit", "increasing", "shuffle"]
+
+
+def best_cut_plan(scene, settings: ShopSettings | None = None, attempts: int = 24) -> CutPlan:
+    """Find a better layout by trying several strategies + shuffle restarts and
+    keeping the best-scoring one. (Good and explainable, not provably optimal.)"""
+    strategies = ["decreasing", "bestfit", "increasing"]
+    strategies += [f"shuffle{i}" for i in range(max(attempts - len(strategies), 0))]
+    best = None
+    for st in strategies:
+        plan = build_cut_plan(scene, settings, strategy=st)
+        if best is None or _plan_key(plan) < _plan_key(best):
+            best = plan
+    if best is not None:
+        best.strategy = "optimized"
+        best.score["strategy_name"] = "optimized"
+    return best
+
+
 def validate_cut_plan(plan: CutPlan) -> list:
     """Return a list of problems ([] means valid): pieces inside stock, no
     overlaps, kerf respected, every item placed-or-warned."""

src/woodshop/gui/bom_window.py

@@ -11,10 +11,9 @@ from PySide6.QtWidgets import (QDialog, QGraphicsRectItem, QGraphicsScene,
                                QPushButton, QTabWidget, QTextEdit, QVBoxLayout, QWidget)
 
 from ..cutlist import _fmt_len, cut_rows, shopping
-from ..cutplan import build_cut_plan
+from ..cutplan import STRATEGIES, best_cut_plan, build_cut_plan
 from ..layout import waste_summary
 
-_ORDERS = ["decreasing", "increasing", "shuffle"]
 _PX = 7.0          # pixels per inch in the layout view
 _PIECE = "#c8965a"
 _WASTE = "#3a3a3a"
@@ -27,6 +26,7 @@ class BomWindow(QDialog):
         self.setWindowTitle("Cut List & BOM")
         self.resize(820, 640)
         self._order = 0
+        self._optimized = False
 
         tabs = QTabWidget()
         tabs.addTab(self._text_tab(self._cut_text()), "Cut List")
@@ -91,22 +91,31 @@ class BomWindow(QDialog):
         self.view = QGraphicsView(self.scene)
         v.addWidget(self.view)
         row = QHBoxLayout()
-        again = QPushButton("Try another arrangement")
+        opt = QPushButton("Find better layout")
-        again.clicked.connect(self._next_arrangement)
+        opt.setToolTip("Try several packing strategies and keep the best-scoring one")
+        opt.clicked.connect(self._optimize)
+        alt = QPushButton("Try alternative")
+        alt.clicked.connect(self._next_arrangement)
         pr = QPushButton("Print…")
         pr.clicked.connect(self._print_layout)
-        row.addWidget(again); row.addStretch(); row.addWidget(pr)
+        row.addWidget(opt); row.addWidget(alt); row.addStretch(); row.addWidget(pr)
         v.addLayout(row)
         self._draw_layout()
         return w
 
+    def _optimize(self) -> None:
+        self._optimized = True
+        self._draw_layout()
+
     def _next_arrangement(self) -> None:
-        self._order = (self._order + 1) % len(_ORDERS)
+        self._optimized = False
+        self._order = (self._order + 1) % len(STRATEGIES)
         self._draw_layout()
 
     def _draw_layout(self) -> None:
         self.scene.clear()
-        plan = build_cut_plan(self.c.scene, strategy=_ORDERS[self._order])
+        plan = (best_cut_plan(self.c.scene) if self._optimized
+                else build_cut_plan(self.c.scene, strategy=STRATEGIES[self._order]))
         names = {p.id: (p.name or p.id) for p in self.c.scene.parts}
         part_of = {it.id: it.part_id for it in plan.items}
         label = lambda iid: names.get(part_of.get(iid, ""), iid)

tests/test_cutplan.py

@@ -71,6 +71,36 @@ def test_json_roundtrip():
     assert validate_cut_plan(plan2) == []
 
 
+def test_plywood_rotation_fits_panel():
+    s = Scene()
+    s.place("ply-3/4", 30, width_in=60)     # 60" wide > 48" sheet — needs rotating
+    plan = build_cut_plan(s)                 # rotation allowed by default
+    sheets = [sp for sp in plan.stock_pieces if sp.is_sheet]
+    assert len(sheets) == 1
+    p = sheets[0].placements[0]
+    assert p.rotated and p.len_in == 60 and p.wid_in == 30
+    assert validate_cut_plan(plan) == []
+
+
+def test_rotation_disabled_flags_unfit():
+    s = Scene()
+    s.place("ply-3/4", 30, width_in=60)
+    plan = build_cut_plan(s, settings=ShopSettings(allow_plywood_rotation=False))
+    assert plan.unplaced and plan.warnings
+
+
+def test_best_cut_plan_is_no_worse():
+    from woodshop.cutplan import _plan_key, best_cut_plan
+    s = Scene()
+    for ln in (50, 46, 30, 30, 20):
+        s.place("2x4", ln)
+    best = best_cut_plan(s)
+    base = build_cut_plan(s, strategy="decreasing")
+    assert _plan_key(best) <= _plan_key(base)
+    assert best.strategy == "optimized"
+    assert validate_cut_plan(best) == []
+
+
 def test_custom_settings_kerf():
     s = Scene()
     s.place("2x4", 48)