lead-acid example notebook intermittently times out in CI #5884

The Example notebooks CI job intermittently fails because docs/source/examples/notebooks/models/lead-acid.ipynb hits nbmake's 300 s cell timeout. The rest of the job takes about 15 minutes for all 89 notebooks, so this looks like a hang rather than a slow solve.

The cell that times out:

t_eval = [0, 3600]
for model in models:
    solver = pybamm.IDAKLUSolver()
    solutions[model] = solver.solve(model, t_eval, inputs={"Current function [A]": 20})

models is [pybamm.lead_acid.LOQS(), pybamm.lead_acid.Full()]. The same cell solved them at the default current (t_eval = [0, 3600 * 17]) a few cells earlier, so the hang is in the 20 A re-solve, or in the QuickPlot that follows in the same cell.

Occurrences (Ubuntu, Python 3.13)

I found no failures of this job between 1 Oct and 7 Oct 17:30 UTC. All four commits from 7 Oct predate #5837 (OpenMP region) and #5864 (KLU AMD ordering), so neither of those caused it. Re-running the job usually passes: main at 30d82e0 and 3e00920 passed.

Next steps

• Reproduce locally by running the cell in a loop to see whether the IDAKLU solve stalls for some inputs, and check what changed on main or in the lockfile around 7 Oct.
• If it is a genuine solver stall, a SolverError or a time limit would be better than a hang.

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