Correct the kept-lines bullet; test .editorconfig with no own line

REPO_POLICIES said an ignore file lacking the closing comment keeps every
line the canonical file has never held; blank lines and comments are
dropped, so it now says entries, in a bullet of its own.

A new scenario covers an .editorconfig lacking the comment with no line
of its own, which the script replaces.

Model: opus-5-5

prompts/REPO_POLICIES.md

@@ -951,9 +951,9 @@ style conventions are in separate documents:
     files is at the top of `script/install`. The script replaces each file and
     keeps only the repo's own entries:
     - in `.gitignore`, `.editorconfig` and `.dockerignore`: the lines below the
-      comment that ends the canonical file, and, in a `.gitignore` or
-      `.dockerignore` lacking that comment, every line the canonical file has
-      never held
+      comment that ends the canonical file
+    - in a `.gitignore` or `.dockerignore` lacking that comment: every entry the
+      canonical file has never held
     - in `.golangci.yml`: the entries the repo added to the `deny` list of the
       `test-support` depguard rule
 

test/update-policy.sh

@@ -737,6 +737,13 @@ test_editorconfig_lacks_canonical_last_line() {
     expect_nothing_written
 }
 
+test_editorconfig_lacks_canonical_last_line_no_own_line() {
+    start_scenario ".editorconfig lacking the canonical last line with no line of its own is replaced"
+    printf 'root = true\n[*]\n' > "$dir/repo/.editorconfig"
+    expect_former_canonical_line_replaced .editorconfig "indent_size = 8"
+    expect_same_as_canonical .editorconfig
+}
+
 test_fetched_golangci_without_deny_list() {
     start_scenario "a fetched .golangci.yml with no deny list stops"
     cat > "$dir/canonical/.golangci.yml" << 'EOF'
@@ -888,6 +895,7 @@ main() {
     test_gitignore_lacks_canonical_last_line
     test_dockerignore_lacks_canonical_last_line
     test_editorconfig_lacks_canonical_last_line
+    test_editorconfig_lacks_canonical_last_line_no_own_line
     test_fetched_golangci_without_deny_list
     test_own_golangci_setting_stops
     test_source_repo_stops