Java 27 and 26: runnable demos and captured output for every JEP, plus version lanes

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01B38FGKKam5SCGgwgduVAh3

docs/output/90-unnamed-and-compact.txt

@@ -0,0 +1,26 @@
+# _ (unnamed variables and patterns) and compact source files with instance main()
+
+$ javac UnnamedVariables.java      (JDK 21, no flag)
+    <repo>/lanes/src/UnnamedVariables.java:12: error: unnamed variables are a preview feature and are disabled by default.
+            if (o instanceof Point(int x, _)) {
+                                           ^
+      (use --enable-preview to enable unnamed variables)
+    1 error
+    exit=1
+
+$ javac UnnamedVariables.java      (JDK 25, no flag)
+    exit=0
+$ java UnnamedVariables      (JDK 25)
+    matched a Point, x = 3, y ignored with _
+    caught NumberFormatException without naming it
+
+$ java CompactHello.java      (JDK 21, no flag)
+    <repo>/lanes/src/CompactHello.java:1: error: unnamed classes are a preview feature and are disabled by default.
+    void main() {
+    ^
+      (use --enable-preview to enable unnamed classes)
+    1 error
+    error: compilation failed
+
+$ java CompactHello.java      (JDK 25, no flag)
+    compact source file: no class, no static, no String[] args