Summary

• derive fanout plane drops from an explicit fanoutPourNetMap
• infer the same layer-to-net mapping from <copperpour> components in the current or enclosing subcircuit
• synthesize the fanout solver's plane buses internally for source-only traces
• preserve each supply drop as an independent connection instead of collapsing same-net pads into one route
• use source-trace names for optional per-drop fanout directions
• pass fanoutRoutingLayers through as the solver's allowed signal escape layers

Why

Plane termination belongs to the board's copper intent. Users should be able to
write a normal source-only trace to net.GND or net.VCC and have fanout drop
it to the matching pour layer without declaring a singleton
BusFanoutTermination.

If a net is poured on multiple layers, core reports the ambiguity and asks for
an explicit fanoutPourNetMap.

Dependency

• Add fanout pour net map props props#766 is merged and released in @tscircuit/props@0.0.599
• this branch now consumes that released version

Main branch sync

• rebased onto core v0.0.1552
• preserves main's multi-port trace support from Fix multi-port traces in the default autorouter #2933
• the getSimpleRouteJsonFromCircuitJson.ts patch is reduced from 102 changed lines to 38

Validation

• focused fanout and formerly failing regression tests — 7 passed, 0 failed
• full CI shard 3 — 311 passed, 0 failed
• full CI shard 4 — 305 passed, 0 failed
• explicit map and copper-pour inference are both covered
• bunx tsc --noEmit
• bun run build