feat(pin): exactly 4 digits, entered on the 4th digit

The keypad has no OK key; the 4th digit submits, so a tap that also
arrives as START can no longer submit a partial PIN (the likely cause
of "Wrong PIN" before the code opened). PINs set by earlier versions
still unlock and are then replaced by a 4-digit one. Opening an entry
ignores a second request from the same tap. A Require PIN sent from
the phone while the watch is locked now applies at the next PIN
instead of waiting for Confirm all. The linter skips .claude.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/test/storage/StorageSupport.mc b/test/storage/StorageSupport.mc
index 51a0c7c..5f2ead3 100644
--- a/test/storage/StorageSupport.mc
+++ b/test/storage/StorageSupport.mc
@@ -143,8 +143,9 @@ class FakeTime extends TimeSource {
 (:test)
 module StorageFixtures {
 
-    const PIN = "246810";
-    const OTHER_PIN = "135799";
+    const PIN = "2468"; // KeyManager.PIN_DIGITS digits, like every new PIN
+    const OTHER_PIN = "1357";
+    const LEGACY_PIN = "246810"; // a 6-digit PIN from before the 4-digit rule
     const ITERATIONS = 2000; // Kdf.MIN_ITERATIONS: the cheapest allowed
 
     // A fake TOTP entry (the secret is the RFC 4226 test key, not a real one).
@@ -205,6 +206,22 @@ module StorageFixtures {
         vault.finishSetPin(job);
     }
 
+    // Store a wrap the way versions before the 4-digit rule did: any 4 to
+    // 10 digits and no PIN-length marker. The session stays locked.
+    function setLegacyPin(store as MemoryBackend, text as String) as Void {
+        var keyManager = new KeyManager(store);
+        var job = new PinJob(pin(text), new [KeyManager.SALT_BYTES]b, ITERATIONS);
+        Jobs.runToCompletion(job, Kdf.ITERATIONS_PER_STEP);
+        keyManager.storeWrap(job, keyManager.newMasterKey());
+        store.deleteValue(KeyManager.PIN_LENGTH_KEY);
+    }
+
+    // True when the store holds the 4-digit PIN marker.
+    function pinMarked(store as MemoryBackend) as Boolean {
+        var marker = store.getValue(KeyManager.PIN_LENGTH_KEY);
+        return marker instanceof Number && marker == KeyManager.PIN_DIGITS;
+    }
+
     // One unlock attempt; true when the PIN was right.
     function unlock(vault as Vault, text as String) as Boolean {
         var job = vault.beginUnlock(pin(text));