diff --git a/.gitignore b/.gitignore
index fa2de04..d35c74c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,7 +3,15 @@
 # because files were unzipped on Windows before being copied into WSL.
 *:Zone.Identifier
 
-# LaTeX build artifacts
+# Build output directory: `pdflatex -output-directory=build` (see CLAUDE.md)
+# puts all generated files here, keeping the repo root clean. Tracked as an
+# (empty) folder via .gitkeep so it exists right after a fresh clone; its
+# generated contents are not tracked.
+build/*
+!build/.gitkeep
+
+# LaTeX build artifacts (in case of compiling without -output-directory)
+*-eps-converted-to.pdf
 *.aux
 *.bbl
 *.bcf
diff --git a/build/.gitkeep b/build/.gitkeep
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/build/.gitkeep