feat: specialized horizontal-row layout for decoupling caps (#15)

[solomonshalom]

Summary

Implements the layout requested in #15 by adding DecouplingCapsHorizontalRowSolver and routing partitions tagged partitionType: \"decoupling_caps\" through it instead of PackSolver2. The general packer is fine for arbitrary chips but produces stacked / scattered layouts for cap groups; this solver lays them out as a single tidy horizontal row matching the acceptable solution image in the issue.

Approach

The pipeline already does the hard work — IdentifyDecouplingCapsSolver finds the cap groups, ChipPartitionsSolver builds dedicated decoupling_caps partitions for them. The missing piece was the per-partition packer.

DecouplingCapsHorizontalRowSolver:

1. Sorts the caps by chipId so the row order is stable across runs (important for snapshot stability and for the outer packer's nearest-neighbor logic).
2. Walks the sorted list along x, advancing by cap.size.x + gap per step, centering the whole row on the origin so the outer PartitionPackingSolver treats the partition as one block to attach next to the main chip's power pins.
3. Applies each cap's first availableRotation (typically 0°), which IdentifyDecouplingCapsSolver already restricts to keep the y+/y- pin pair upright.

gap defaults to partition.decouplingCapsGap → partition.chipGap, exactly mirroring the fallback chain that SingleInnerPartitionPackingSolver already uses when configuring PackSolver2. Callers wanting a tighter or wider row can pass gap explicitly.

The solver shape (step / solved / failed / error / packedComponents) is assignment-compatible with PackSolver2, so the parent inner-partition packer routes through whichever child it instantiated without any special-casing in the layout-extraction code path.

Files

• New lib/solvers/DecouplingCapsHorizontalRowSolver/DecouplingCapsHorizontalRowSolver.ts — solver + visualize.
• Edit lib/solvers/PackInnerPartitionsSolver/SingleInnerPartitionPackingSolver.ts — branch on partitionType === \"decoupling_caps\" to instantiate the row solver, otherwise stay on PackSolver2. Loosened the activeSubSolver and createLayoutFromPackingResult types to accept either child shape.

Tests (16 new)

Unit tests in tests/DecouplingCapsHorizontalRowSolver/DecouplingCapsHorizontalRowSolver.test.ts:

• empty / single / multi-cap rows
• horizontal alignment on shared y-axis
• uniform x spacing between adjacent centers
• row centered on the origin
• explicit gap parameter overrides partition fallbacks
• decouplingCapsGap fallback used when gap unset
• chipGap fallback used when decouplingCapsGap missing
• non-uniform cap widths produce a correctly-spaced centered row
• deterministic chipId-based lex ordering
• rotation taken from first availableRotation, defaulting to 0
• packedComponents shape matches PackSolver2 consumer expectations
• single-step completion regardless of cap count
• idempotency across re-runs
• visualize() emits one rect per cap with correct dimensions

Integration tests in tests/DecouplingCapsHorizontalRowSolver/integration.test.ts:

• decoupling_caps partition routes through the row solver and produces the expected y-aligned, uniformly-spaced layout via SingleInnerPartitionPackingSolver.
• default partitions still drive PackSolver2 (regression guard so the new branch can never silently capture non-decap partitions).

Test plan

• bun test tests/DecouplingCapsHorizontalRowSolver/ — 16 pass, 0 fail.
• bun test (full suite) — 33 pass + 1 skip + 1 pre-existing failure + 1 pre-existing import error. No new failures introduced.
• bun run format — biome clean.
• bunx tsc --noEmit — no new type errors involving the new code.

/claim #15

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