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GRT: heap underflow during 3D maze routing #10156

@mole99

Description

@mole99

Describe the bug

After diode insertion, GRT aborts with [ERROR GRT-0183] Net net185: heap underflow during 3D maze routing..

Expected Behavior

3D maze routing completes without error.

Environment

A recent OpenROAD version from 2026-04-12

To Reproduce

To reproduce, simply extract the zip and run ./run.sh: reproducible.zip

Relevant log output

Reading timing models for corner nom_tt_025C_1v80…
Reading timing library for the 'nom_tt_025C_1v80' corner at './files/home/leo/.ciel/ciel/sky130/versions/8afc8346a57fe1ab7934ba5a6056ea8b43078e71/sky130A/libs.ref/sky130_fd_sc_hd/lib/sky130_fd_sc_hd__tt_025C_1v80.lib'…
Reading OpenROAD database at './files/home/leo/Repositories/tt-fabulous-sky-26a/runs/RUN_2026-04-16_08-36-47/39-openroad-globalrouting/tt_um_fabulous_sky_26a.odb'…
Reading design constraints file at './files/nix/store/33fnv6qjdp6wslmjybwc6z0wab2vrc7l-python3-3.13.9-env/lib/python3.13/site-packages/librelane/scripts/base.sdc'…
[INFO] Using clock clk…
[INFO] Setting output delay to: 2
[INFO] Setting input delay to: 2
[INFO] Setting load to: 0.033442
[INFO] Setting clock uncertainty to: 0.25
[INFO] Setting clock transition to: 0.15
[INFO] Setting timing derate to: 5%
+ repair_antennas sky130_fd_sc_hd__diode_2 -iterations 3 -ratio_margin 10 -allow_congestion
[INFO GRT-0012] Found 56 antenna violations.
[INFO GRT-0302] Inserted 38 jumpers for 24 nets.
[INFO GRT-0012] Found 33 antenna violations.
[INFO GRT-0015] Inserted 124 diodes.
[ERROR GRT-0183] Net net185: heap underflow during 3D maze routing.
Error: antenna_repair.tcl, 27 GRT-0183

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