Rebuild Displays around the canvas, and let the transaction keep color

Claude-Session: https://claude.ai/code/session_01Ms2FbjQy31TVf3CEvQhGM8

config/dot/quickshell/displays-harness.qml

@@ -112,6 +112,30 @@ ShellRoot {
             });
         }
 
+        // The extended record — vrr override, colour profile, bit depth, SDR
+        // trim, mirroring — merged one field at a time, which is how every
+        // control on the page changes it. Base64 for the reason restorePlan
+        // documents above: `qs ipc call` splits JSON that looks like an array
+        // of objects into one argument per object.
+        function applyRecordFixture(output: string, patchB64: string): bool {
+            return Displays.applyRecord(output, JSON.parse(Qt.atob(patchB64)));
+        }
+
+        // matchesLayout as a pure function. The readback carve-outs — a
+        // mirrored output's position, a framebuffer format Panama does not
+        // recognise — are decisions about what NOT to assert, and proving them
+        // through a compositor would mean owning a compositor that mirrors.
+        function layoutMatch(monitorsB64: string, layoutB64: string): bool {
+            return Displays.matchesLayout(JSON.parse(Qt.atob(monitorsB64)),
+                JSON.parse(Qt.atob(layoutB64)));
+        }
+
+        // A settings.json written before any of the new fields existed is the
+        // common case on every machine that has this installed today.
+        function persistedEntryValid(entryB64: string): bool {
+            return Displays.isPersistedLayoutEntry(JSON.parse(Qt.atob(entryB64)));
+        }
+
         function expireApplyVerification(): void {
             Displays.verificationTimedOut();
         }