The guard added earlier could never trigger. tools/render_mermaid.py has no
nonzero exit path — its own docstring said "Exits 0 even if some/all fail
(non-fatal)" — so `if ! render_mermaid.py ...; then exit 1; fi` never ran its
body, and a build that rendered zero diagrams still passed. Reproduced by
running the script with no Chrome on PATH: it printed the fallback warning and
exited 0.
Adds a --strict flag that exits 1 when Chrome is missing or any diagram fails
to render, and passes it from every workflow invocation. The default stays
lenient so local mobile-reader builds keep working, which is what the exit-0
behaviour was actually for.
Verified both directions: with no Chrome, --strict exits 1 and the default
exits 0; against the real book with Chrome, --strict renders every diagram and
exits 0.
Renders Mermaid to SVG via the workflow's Chrome, pandoc --mathml, assembles a
single self-contained responsive HTML reader, and attaches <repo>-<tag>.html to
the GitHub Release next to the PDF. Non-blocking (continue-on-error).
yeasy