fix: keep power and ground rail recovery in the preferred direction

[seveibar]

Summary

Automatic rail recovery can send AM3352 J_SD.4 down several units to reach J_I2C's V3V3 rail. Prefer a local label when an optional connection travels more than 1 schematic unit downward toward power, or 1 unit upward toward ground. Also cap total vertical travel at 4 units, even in the preferred direction; lateral travel does not consume this budget.

Measure the routed path from each candidate terminal to the shared label, stopping at that label. A large height difference between terminals is valid when both approach the label in the correct direction. For example, V_IN.2 and C1.2 in bug-report-20260707T141421Z remain connected because their shared GND anchor lies below both pins; that snapshot is unchanged.

• Preview label placement and collision relocation for new shared rails; use retained labels directly for late recovery.
• Count cumulative vertical and wrong-direction travel along the same connected path, including bends, junctions, and labels inside segments. Preserve alternative paths when one uses less of the vertical budget.
• Apply the preference in long-distance and final label-to-trace recovery. Primary routing, explicit wires, same-component buses, and signals retain their existing behavior.
• Resolve rail direction and net aliases through connectivity and availableNetLabelOrientations.

On AM3352, J_SD receives its own upward V3V3 label. J_SPI and J_I2C use separate ground labels, while their power pins can share an upper V3V3 rail.

Review

Two recovery solvers use a shared policy and path-traversal helper. Regression tests cover the 1-unit boundary in both directions, endpoint reversal, correct-direction joins, aliases, explicit wiring, detours, junctions, the reported GND connection, C1’s excessive 7.42-unit drop in bug-report-20260716T144856Z, and the AM3352 output. C1 now uses a local GND label. There are 19 reviewed snapshot changes relative to the merged reproduction baseline.

• AM3352 before
• AM3352 after

This is a recovery preference based on the available label layout, not a global constraint on primary wiring or every subsequent layout operation.

Validation

• bun test: 429 pass, 4 skip, 0 fail across 264 files
• bunx tsc --noEmit: passes
• Biome formatting for changed TypeScript and git diff --check: pass
• Reviewed all 19 changed schematic snapshots against the merged baseline

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Project	Deployment	Actions	Updated
schematic-trace-solver	Ready	Preview	Sep 16, 2026 4:17am UTC