The page cache is one directory per document; the shipped suites measure under a UTF-8 locale (from dev 3321e7c9e36e)

tst/editor/vim_feature_test.vim

@@ -20,6 +20,11 @@
 "
 " Writes PASS/FAIL lines to $KT_OUT; exits nonzero if anything failed.
 
+" The buffer text below is UTF-8 (the umlauts of the multibyte case).  Vim
+" takes 'encoding' from the locale, and under a C locale that is latin1,
+" where each umlaut is two characters and the jump lands two columns short
+" -- a failure of this file, not of the plugin (TODO 78, 2026-10-19).
+set encoding=utf-8
 let s:results = []
 function! s:Check(name, ok, ...) abort
   let detail = (a:ok || !a:0) ? '' : ' -- ' . string(a:1)

tst/kdesc_test.sh

@@ -49,6 +49,9 @@ else
 fi
 
 # shows NAME PATTERN CMD... — exits 0 and the output matches PATTERN.
+# The matching grep alone runs under a UTF-8 locale (TODO 78): under C its
+# "." counts bytes, so the width test 10a fails and 10b can falsely pass; the
+# command itself keeps the caller's locale.
 shows() {
     local name="$1" pattern="$2"; shift 2
     local out status
@@ -56,7 +59,7 @@ shows() {
     if [ $status -gt 128 ]; then
         echo "${red}FAIL${reset} $name — died by signal $((status-128))"; FAIL=$((FAIL+1)); return
     fi
-    if printf '%s' "$out" | grep -Eq -- "$pattern"; then
+    if printf '%s' "$out" | LC_ALL=C.UTF-8 grep -Eq -- "$pattern"; then
         echo "${green}PASS${reset} $name"; PASS=$((PASS+1))
     else
         echo "${red}FAIL${reset} $name — no line matching [$pattern]"
@@ -67,7 +70,7 @@ shows() {
 # absent NAME PATTERN CMD... — the output does NOT match PATTERN.
 absent() {
     local name="$1" pattern="$2"; shift 2
-    if limited "$@" 2>&1 | plain | grep -Eq -- "$pattern"; then
+    if limited "$@" 2>&1 | plain | LC_ALL=C.UTF-8 grep -Eq -- "$pattern"; then
         echo "${red}FAIL${reset} $name — unexpected match [$pattern]"; FAIL=$((FAIL+1))
     else
         echo "${green}PASS${reset} $name"; PASS=$((PASS+1))

tst/kdiag_test.sh

@@ -80,6 +80,11 @@ pass() { echo "${green}PASS${reset} $1"; PASS=$((PASS + 1)); }
 fail() { echo "${red}FAIL${reset} $1"; [ -n "$2" ] && echo "       $2"; FAIL=$((FAIL + 1)); }
 
 # shows NAME PATTERN KDIAG_ARGS... — exits 0 and the output matches PATTERN.
+# The MATCHING grep runs under a UTF-8 locale whatever the caller's: under C
+# its "." matches a byte, and a pattern like "⟨@i.⟩" over a three-byte
+# subscript fails as if kdiag were wrong (cases 28 and 30; TODO 78).  Only
+# the grep: kdiag itself runs under the caller's locale, so a locale
+# dependency in the command would still show.
 shows() {
     local name="$1" pattern="$2"; shift 2
     run "$KDIAG" "$@"
@@ -89,7 +94,7 @@ shows() {
     if [ "$STATUS" -ne 0 ]; then
         fail "$name" "exit $STATUS: $(printf '%s' "$OUT" | head -2)"; return
     fi
-    if printf '%s' "$OUT" | grep -Eq -- "$pattern"; then
+    if printf '%s' "$OUT" | LC_ALL=C.UTF-8 grep -Eq -- "$pattern"; then
         pass "$name"
     else
         fail "$name" "no match for [$pattern]; got: $(printf '%s' "$OUT" | head -2)"
@@ -106,7 +111,7 @@ absent() {
     if [ "$STATUS" -ne 0 ]; then
         fail "$name" "exit $STATUS: $(printf '%s' "$OUT" | head -2)"; return
     fi
-    if printf '%s' "$OUT" | grep -Eq -- "$pattern"; then
+    if printf '%s' "$OUT" | LC_ALL=C.UTF-8 grep -Eq -- "$pattern"; then
         fail "$name" "unexpected match [$pattern]"
     else
         pass "$name"
@@ -123,7 +128,7 @@ reports() {
     if [ "$STATUS" -eq 0 ]; then
         fail "$name" "expected a nonzero exit, got 0"; return
     fi
-    if printf '%s' "$OUT" | grep -Eq -- "$pattern"; then
+    if printf '%s' "$OUT" | LC_ALL=C.UTF-8 grep -Eq -- "$pattern"; then
         pass "$name"
     else
         fail "$name" "no match for [$pattern]; got: $(printf '%s' "$OUT" | head -2)"
@@ -245,7 +250,7 @@ reports "24a. the error advice names a way kdiag has" '@read sks/sks\.k @' \
 absent_in_error() {
     local name="$1" pattern="$2"; shift 2
     run "$KDIAG" "$@"
-    if printf '%s' "$OUT" | grep -Eq -- "$pattern"; then
+    if printf '%s' "$OUT" | LC_ALL=C.UTF-8 grep -Eq -- "$pattern"; then
         fail "$name" "unexpected match [$pattern]"
     else
         pass "$name"