Rework proof script to use existing proof/ Java files instead of YAML proofCode

The existing proof/ directory (from a parallel branch) contains 105 individual
JBang scripts - one per pattern - that were missed in the initial approach.

Changes:
- Add all 105 proof/**/*.java scripts from proof/ directory
- Rewrite html-generators/proof.java to run proof/**/*.java via jbang
  instead of parsing YAML proofCode fields through JShell
- Revert the proofCode field additions from 10 YAML content files
- Revert proofCode from generate.java/generate.py EXCLUDED_KEYS
- Revert proofCode from content/template.json
- Update .github/workflows/proof.yml to trigger on proof/** changes
- Update html-generators/README.md, CONTRIBUTING.md, and
  .github/copilot-instructions.md to document the proof/ directory

Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Author: Copilot

.github/copilot-instructions.md

@@ -49,6 +49,10 @@ Run `jbang html-generators/generate.java` to rebuild all generated files from th
 
 ```
 content/            # English content JSON files (source of truth, one per pattern)
+proof/              # Proof scripts — one JBang .java file per pattern, proving it compiles
+  language/         # e.g. proof/language/TypeInferenceWithVar.java
+  collections/      # e.g. proof/collections/ImmutableListCreation.java
+  ...               # mirrors content/ category structure
 translations/       # All i18n artifacts
   strings/          # UI strings per locale (en.yaml, es.yaml, pt-BR.yaml)
   content/          # Translated pattern files per locale (partial, translatable fields only)
@@ -100,8 +104,7 @@ Each `content/category/slug.json` file has this structure:
   ],
   "docs": [
     { "title": "Javadoc or Guide Title", "href": "https://docs.oracle.com/..." }
-  ],
-  "proofCode": "// Optional: self-contained JShell snippet proving the modern approach works.\n// Run with: jbang html-generators/proof.java"
+  ]
 }
 ```
 
@@ -139,7 +142,8 @@ Categories and their display names are defined in `html-generators/categories.pr
 1. Create `content/category/new-slug.json` with all required fields
 2. Update `prev`/`next` in the adjacent patterns' JSON files
 3. Run `jbang html-generators/generate.java`
-4. (Optional) Create translated content files under `translations/content/{locale}/category/new-slug.json` with only translatable fields — or let the AI translation workflow handle it
+4. Add a proof script at `proof/category/SlugName.java` (JBang, `//JAVA 25+`) — run `jbang html-generators/proof.java` to verify
+5. (Optional) Create translated content files under `translations/content/{locale}/category/new-slug.json` with only translatable fields — or let the AI translation workflow handle it
 
 ## Internationalization (i18n)
 

.github/workflows/proof.yml

@@ -4,12 +4,12 @@ on:
   push:
     branches: [main]
     paths:
-      - 'content/**'
+      - 'proof/**'
       - 'html-generators/proof.java'
       - '.github/workflows/proof.yml'
   pull_request:
     paths:
-      - 'content/**'
+      - 'proof/**'
       - 'html-generators/proof.java'
   workflow_dispatch:
 

CONTRIBUTING.md

@@ -9,7 +9,7 @@ Contributions are welcome! Content is managed as YAML files — never edit gener
 3. Copy [`content/template.json`](content/template.json) as a starting point for all required fields (see the [snippet schema](.github/copilot-instructions.md) for details)
 4. Update the `prev`/`next` fields in adjacent pattern files to maintain navigation
 5. Run `jbang html-generators/generate.java` to verify your changes build correctly
-6. Optionally add a `proofCode` field — a self-contained JShell snippet that proves the modern approach works. Run `jbang html-generators/proof.java` to validate it.
+6. Add a proof script at `proof/<category>/SlugName.java` that uses the modern approach and run `jbang html-generators/proof.java` to verify it passes
 7. Open a pull request
 
 Please ensure JDK version labels only reference the version where a feature became **final** (non-preview).

content/collections/immutable-list-creation.yaml

@@ -47,11 +47,3 @@ docs:
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/List.html#of()"
 - title: "Collections Factory Methods (JEP 269)"
   href: "https://openjdk.org/jeps/269"
-proofCode: |-
-  var list = List.of("a", "b", "c");
-  if (list.size() != 3) throw new AssertionError("expected 3 elements");
-  try {
-      list.add("d");
-      throw new AssertionError("should have thrown UnsupportedOperationException");
-  } catch (UnsupportedOperationException ok) {}
-  IO.println("immutable list: OK - " + list);

content/concurrency/virtual-threads.yaml

@@ -47,13 +47,3 @@ docs:
   href: "https://openjdk.org/jeps/444"
 - title: "Thread.ofVirtual()"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Thread.html#ofVirtual()"
-proofCode: |-
-  var results = new java.util.concurrent.CopyOnWriteArrayList<String>();
-  var threads = new ArrayList<Thread>();
-  for (int i = 0; i < 5; i++) {
-      int idx = i;
-      threads.add(Thread.startVirtualThread(() -> results.add("vt-" + idx)));
-  }
-  for (var t : threads) t.join();
-  if (results.size() != 5) throw new AssertionError("expected 5 results, got: " + results.size());
-  IO.println("virtual threads: OK - " + results.size() + " threads ran");

content/datetime/java-time-basics.yaml

@@ -51,12 +51,3 @@ docs:
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/time/LocalTime.html"
 - title: "LocalDateTime"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/time/LocalDateTime.html"
-proofCode: |-
-  import java.time.*;
-  var date = LocalDate.of(2025, Month.JANUARY, 15);
-  var time = LocalTime.of(14, 30);
-  if (date.getMonthValue() != 1) throw new AssertionError("expected January=1, got: " + date.getMonthValue());
-  if (time.getHour() != 14) throw new AssertionError("expected hour=14, got: " + time.getHour());
-  var now = Instant.now();
-  if (now == null) throw new AssertionError("Instant.now() returned null");
-  IO.println("java.time basics: OK - " + date + " " + time);

content/language/pattern-matching-instanceof.yaml

@@ -44,11 +44,3 @@ related:
 docs:
 - title: "Pattern Matching for instanceof (JEP 394)"
   href: "https://openjdk.org/jeps/394"
-proofCode: |-
-  Object obj = "Hello, pattern matching!";
-  if (obj instanceof String s) {
-      IO.println("length=" + s.length());
-  } else {
-      throw new AssertionError("should have matched String");
-  }
-  IO.println("pattern matching instanceof: OK");

content/language/records-for-data-classes.yaml

@@ -46,8 +46,3 @@ docs:
   href: "https://openjdk.org/jeps/395"
 - title: "Record class"
   href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Record.html"
-proofCode: |-
-  public record Point(int x, int y) {}
-  var p = new Point(1, 2);
-  if (p.x() != 1 || p.y() != 2) throw new AssertionError("accessor mismatch");
-  IO.println("records: OK - " + p);

content/language/switch-expressions.yaml

@@ -53,12 +53,3 @@ related:
 docs:
 - title: "Switch Expressions (JEP 361)"
   href: "https://openjdk.org/jeps/361"
-proofCode: |-
-  var day = "MONDAY";
-  String msg = switch (day) {
-      case "MONDAY"  -> "Start";
-      case "FRIDAY"  -> "End";
-      default        -> "Mid";
-  };
-  if (!"Start".equals(msg)) throw new AssertionError("unexpected: " + msg);
-  IO.println("switch expressions: OK - " + msg);

content/language/text-blocks-for-multiline-strings.yaml

@@ -49,12 +49,3 @@ docs:
   href: "https://openjdk.org/jeps/378"
 - title: "Text Blocks Guide"
   href: "https://docs.oracle.com/en/java/javase/25/language/text-blocks.html"
-proofCode: |-
-  String json = """
-      {
-        "name": "Duke",
-        "age": 30
-      }""";
-  if (!json.contains("Duke")) throw new AssertionError("text block content missing");
-  if (!json.contains("\n")) throw new AssertionError("text block should contain real newlines");
-  IO.println("text blocks: OK");