diff --git a/CLAUDE.md b/CLAUDE.md
index 2383974f..19e056e4 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -23,10 +23,12 @@ saying what is now true, not what was done.
 
 ## Tests
 
-`dune test --root .` must be green before a lane reports; grep its output for
-FAIL, since the exit code alone has lied. `@checks` (`@page`, `@x86`, `@cells`),
-`@sanitize` and `@valgrind` are slow and run once between batches of lanes, with
-the author's permission, never inside a lane. ASan misses uninitialised stack
+A lane never runs the full `dune test`: it builds with `-j 2` and runs only the
+programs and test executables its change touches, one at a time, and lists them in
+its report. After about five lanes merge, one tester agent runs `dune test --root .`
+on master and fixes what broke; grep its output for FAIL, since the exit code alone
+has lied. `@checks` (`@page`, `@x86`, `@cells`), `@sanitize` and `@valgrind` are
+slow and run only with the author's permission. ASan misses uninitialised stack
 reads; `@valgrind` catches them.
 
 ## Evidence