From 2a8d354b58daa3e3450b72835565cc46fb413c25 Mon Sep 17 00:00:00 2001
From: josh <josh@thewrightserver.net>
Date: Sat, 9 May 2026 09:20:44 -0400
Subject: [PATCH] chore(02-01): eslint sim-purity rule + Date.now violator
 fixture

- eslint.config.js block 3: no-restricted-syntax bans Date.now() and
  setInterval() inside src/sim/**, with src/sim/scheduler/clock.ts as
  the single allowed wall-clock owner (CONTEXT D-33, RESEARCH Pitfall 1)
- date-now-violator.ts deliberate-violation fixture (excluded from
  default lint by Block 1's top-level ignores; the programmatic ESLint
  test passes ignore: false to override)
- lint-firewall.test.ts gains 2 new cases: positive (rule fires on
  violator) + negative (rule does NOT fire on clock.ts the one exception)
- Existing CORE-10 firewall test left untouched and remains green
---
 eslint.config.js                              | 48 +++++++++++++++++++
 .../__test_violation__/date-now-violator.ts   | 14 ++++++
 .../__test_violation__/lint-firewall.test.ts  | 34 +++++++++++++
 3 files changed, 96 insertions(+)
 create mode 100644 src/sim/__test_violation__/date-now-violator.ts

diff --git a/eslint.config.js b/eslint.config.js
index d1e35b1..619f8d8 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -49,6 +49,54 @@ export default [
     ],
   },
 
+  // ---------------------------------------------------------------------
+  // 3. Phase-2 sim-purity rule (CONTEXT D-33, RESEARCH Pitfall 1).
+  //
+  // Bans Date.now() and setInterval() inside src/sim/** to enforce the
+  // "Sim modules are pure — no Date.now(), no setInterval" rule from
+  // CLAUDE.md Code Style. The single allowed wall-clock owner is
+  // src/sim/scheduler/clock.ts (which exports the Clock interface and
+  // the wallClock + FakeClock implementations).
+  //
+  // Severity is `error` so `npm run lint --max-warnings 0` fails on a
+  // violation. The deliberate-violation fixture under
+  // src/sim/__test_violation__/ is excluded; it exists ONLY to be lint-
+  // tested by Task 3's Vitest test (which runs ESLint programmatically
+  // with `ignore: false`).
+  // ---------------------------------------------------------------------
+  {
+    files: ['src/sim/**/*.{ts,tsx}'],
+    // Per-block ignores. Note: src/sim/__test_violation__/** is NOT
+    // listed here even though it's globally ignored by Block 1 — the
+    // programmatic ESLint test (with `ignore: false`) overrides the
+    // global ignore, and we WANT the rule to apply to the violator
+    // fixture in that test path so the test can assert it fires.
+    ignores: ['src/sim/scheduler/clock.ts'],
+    languageOptions: {
+      parser: tseslint.parser,
+      parserOptions: {
+        ecmaVersion: 'latest',
+        sourceType: 'module',
+        ecmaFeatures: { jsx: true },
+      },
+    },
+    rules: {
+      'no-restricted-syntax': [
+        'error',
+        {
+          selector: "CallExpression[callee.object.name='Date'][callee.property.name='now']",
+          message:
+            "src/sim/** must inject time; only src/sim/scheduler/clock.ts may read Date.now() (CONTEXT D-33).",
+        },
+        {
+          selector: "CallExpression[callee.name='setInterval']",
+          message:
+            "src/sim/** must not use setInterval; the scheduler drives ticks via the Phaser game loop (CORE-02).",
+        },
+      ],
+    },
+  },
+
   // ---------------------------------------------------------------------
   // 2. Phase-1 architectural firewall (CORE-10).
   //
diff --git a/src/sim/__test_violation__/date-now-violator.ts b/src/sim/__test_violation__/date-now-violator.ts
new file mode 100644
index 0000000..b1f0d59
--- /dev/null
+++ b/src/sim/__test_violation__/date-now-violator.ts
@@ -0,0 +1,14 @@
+// DELIBERATE VIOLATION OF CONTEXT D-33 — DO NOT USE OUTSIDE THE FIREWALL TEST.
+//
+// This file lives under src/sim/__test_violation__/ and is excluded from
+// `npm run lint` via the `ignores` block in eslint.config.js. Its sole
+// purpose is to be lint-tested by lint-firewall.test.ts to prove the
+// no-restricted-syntax rule (Phase 2 sim-purity) actually fires.
+//
+// The Vitest test runs ESLint programmatically with `ignore: false`
+// against this file and asserts that `no-restricted-syntax` fires with
+// the D-33 message.
+
+export function violator(): number {
+  return Date.now(); // intentional violation — Phase 2 Plan 02-01 Task 3
+}
diff --git a/src/sim/__test_violation__/lint-firewall.test.ts b/src/sim/__test_violation__/lint-firewall.test.ts
index 5675a47..6686bae 100644
--- a/src/sim/__test_violation__/lint-firewall.test.ts
+++ b/src/sim/__test_violation__/lint-firewall.test.ts
@@ -47,3 +47,37 @@ describe('CORE-10: src/sim/ cannot import from src/render/ or src/ui/', () => {
     expect(combined).toMatch(/render|ui/i);
   });
 });
+
+describe('Phase 2 sim-purity rule (CONTEXT D-33)', () => {
+  it('eslint flags Date.now() inside src/sim/** as no-restricted-syntax', async () => {
+    const eslint = new ESLint({
+      overrideConfigFile: resolve(process.cwd(), 'eslint.config.js'),
+      ignore: false,
+    });
+    const fixturePath = resolve(
+      process.cwd(),
+      'src/sim/__test_violation__/date-now-violator.ts',
+    );
+    const results = await eslint.lintFiles([fixturePath]);
+
+    expect(results).toHaveLength(1);
+    const violations = results[0].messages.filter(
+      (m) => m.ruleId === 'no-restricted-syntax',
+    );
+    expect(violations.length).toBeGreaterThanOrEqual(1);
+    expect(violations[0].message).toMatch(/inject time|D-33/);
+  });
+
+  it('does NOT flag Date.now() inside src/sim/scheduler/clock.ts (the one exception)', async () => {
+    const eslint = new ESLint({
+      overrideConfigFile: resolve(process.cwd(), 'eslint.config.js'),
+      ignore: false,
+    });
+    const clockPath = resolve(process.cwd(), 'src/sim/scheduler/clock.ts');
+    const results = await eslint.lintFiles([clockPath]);
+    const noRestrictedViolations = results[0].messages.filter(
+      (m) => m.ruleId === 'no-restricted-syntax',
+    );
+    expect(noRestrictedViolations).toHaveLength(0);
+  });
+});