TeX capacity exceeded when building repeatable documentation pipelines

TeX capacity exceeded

The goal is to establish a repeatable CI build that compiles the same LaTeX source with pdftex, XeTeX and LuaTeX without encountering the "TeX capacity exceeded" error.

Because each engine imposes different default limits on token stacks, register counts and auxiliary file handling, a preamble that succeeds under XeTeX or LuaTeX may fail under pdftex, and repeated runs can accumulate .aux/.log files that push the token count over the threshold only on later builds.

• What is the maximum number of auxiliary files (or total token count) that pdftex, XeTeX and LuaTeX can tolerate before the capacity error is raised?
• How can engine‑specific capacity parameters be tuned to obtain deterministic builds across all three back‑ends without merely masking the underlying resource usage?