auto selects pipeline7 for late routing phases with preloaded traces and exhausts iterations

Summary

A later autorouting phase from an RV1106G2 board contains 4 remaining connections, 389 obstacles, and 205 traces produced by earlier phases. The auto preset reaches TscircuitAutorouter without an explicit autorouterVersion, so core selects AutoroutingPipelineSolver7_MultiGraph.

Pipeline 7 repeatedly rips up and retries the four routes until it exhausts its iteration budget. The same exact Simple Route JSON is solved by AutoroutingPipelineSolver9_PreloadedTraceGraph.

Reproduction

1. Use the byte-identical SRJ fixture in tscircuit/core#3292.
2. Instantiate the default/auto TscircuitAutorouter, or run the fixture directly with AutoroutingPipelineSolver7_MultiGraph.
3. Observe that core selects Pipeline 7 and the full solve fails.
4. Run the same input with AutoroutingPipelineSolver9_PreloadedTraceGraph, as demonstrated in tscircuit/tscircuit-autorouter#2168.

Core fixture and labeled snapshot: https://github.com/tscircuit/core/pull/3292

Autorouter fixture and solved snapshot: https://github.com/tscircuit/tscircuit-autorouter/pull/2168

Observed behavior

• Pipeline 7 fails with all 4 remaining connections unsolved.
• Approximately 2,000,000 graph iterations are performed.
• 57,975 global rerips are performed.
• Runtime is approximately 112–155 seconds.
• The public auto configuration gives no indication that a preloaded-trace-aware pipeline is needed.

Expected behavior

autorouter="auto" should complete a later routing phase containing existing traces, without requiring the board author to know and explicitly select an internal beta pipeline.

Comparison

On the same SRJ input, Pipeline 9:

• solves all 4 remaining connections;
• preserves the 205 preloaded traces and returns 209 total traces;
• completes in approximately 106,809 iterations.

Likely fix area

The selection occurs in lib/utils/autorouting/CapacityMeshAutorouter.ts. A possible direction is to select the preloaded-trace-aware solver when auto receives an input with existing traces. Pipeline 9 should not be made the unconditional global default because other preloaded-trace cases, including autorouter bugreport91, still need coverage or repair.

A regression should verify both:

• late-phase inputs with preloaded traces choose a solver that completes this fixture; and
• ordinary inputs without preloaded traces retain their existing behavior.

Start in lib/utils/autorouting/CapacityMeshAutorouter.ts and inspect how auto selects a solver when existing traces are present. Reproduce with the byte-identical SRJ fixture from tscircuit/core#3292 and compare Pipeline 7 with the solved Pipeline 9 case in tscircuit/tscircuit-autorouter#2168. Done means the late-phase fixture completes while ordinary inputs retain their current behavior.