feat: specialized linear layout for decoupling capacitor partitions

lib/solvers/PackInnerPartitionsSolver/SingleInnerPartitionPackingSolver.ts

@@ -38,6 +38,14 @@ export class SingleInnerPartitionPackingSolver extends BaseSolver {
   }
 
   override _step() {
+    // For decoupling cap partitions, use a clean linear row layout
+    // instead of the general PackSolver2 to avoid messy overlapping
+    if (this.partitionInputProblem.partitionType === "decoupling_caps") {
+      this.layout = this.createLinearDecouplingCapLayout()
+      this.solved = true
+      return
+    }
+
     // Initialize PackSolver2 if not already created
     if (!this.activeSubSolver) {
       const packInput = this.createPackInput()
@@ -64,6 +72,46 @@ export class SingleInnerPartitionPackingSolver extends BaseSolver {
     }
   }
 
+  /**
+   * Arranges decoupling capacitors in a clean horizontal row centered at
+   * the origin. Chips are sorted by chipId for deterministic, reproducible
+   * ordering and spaced evenly using decouplingCapsGap (falling back to
+   * chipGap when not set).
+   */
+  private createLinearDecouplingCapLayout(): OutputLayout {
+    const chips = Object.entries(this.partitionInputProblem.chipMap).sort(
+      ([a], [b]) => a.localeCompare(b),
+    )
+
+    const gap =
+      this.partitionInputProblem.decouplingCapsGap ??
+      this.partitionInputProblem.chipGap
+
+    // Calculate total width of the row
+    const totalChipWidth = chips.reduce((sum, [, chip]) => sum + chip.size.x, 0)
+    const totalGapWidth = Math.max(0, chips.length - 1) * gap
+    const totalWidth = totalChipWidth + totalGapWidth
+
+    // Place chips left-to-right, centered around x=0
+    const chipPlacements: Record<string, Placement> = {}
+    let currentX = -totalWidth / 2
+
+    for (const [chipId, chip] of chips) {
+      currentX += chip.size.x / 2
+      chipPlacements[chipId] = {
+        x: currentX,
+        y: 0,
+        ccwRotationDegrees: 0,
+      }
+      currentX += chip.size.x / 2 + gap
+    }
+
+    return {
+      chipPlacements,
+      groupPlacements: {},
+    }
+  }
+
   private createPackInput(): PackInput {
     // Fall back to filtered mapping (weak + strong)
     const pinToNetworkMap = createFilteredNetworkMapping({