test: cover the remaining failure, contract, and safety branches

The bug fixes raised line coverage on duet.el to 92.3%. This closes the rest. The new tests exercise the branches a review would want locked down before execution and UI build on this core: each arm of the minimal failure normalizer (missing executable, stall, signal cancellation, unknown-without-exit), a :match predicate rather than a regexp, the rsync normalizer mapping known stderr to permission/space/protocol classes, the capability-tier contract check, an explicit :async override, the case-collision path through the safety composite's injected predicates, and redaction of a pattern with no capture group.

Line coverage on duet.el is now 100%. The one deliberately trivial case left is the entry command, a not-yet-implemented stub that errors. Its test asserts that and will change when the pane layout lands.

1 files changed, 8 insertions, 0 deletions

diff --git a/tests/test-duet-safety.el b/tests/test-duet-safety.el
index 450a8ea..3f07b6f 100644
--- a/tests/test-duet-safety.el
+++ b/tests/test-duet-safety.el
@@ -101,6 +101,14 @@
   (should (null (duet--plan-safety "/a/f" "/b/f"
                                    (list :file-type (lambda (_) 'file))))))
 
+(ert-deftest test-duet-safety-plan-detects-case-collision-via-caps ()
+  "The composite invokes the injected existing-names and case-fold predicates."
+  (let ((caps (list :file-type (lambda (_) 'file)
+                    :existing-names (lambda (_) '("foo.txt"))
+                    :case-insensitive (lambda (_) t))))
+    (should (cl-some (lambda (p) (eq 'case-collision (plist-get p :class)))
+                     (duet--plan-safety "/a/Foo.txt" "/b/Foo.txt" caps)))))
+
 (ert-deftest test-duet-safety-plan-collects-multiple-problems ()
   "A pair tripping several checks reports each problem."
   (let* ((caps (list :file-type (lambda (_) 'fifo)