fix: typecheck hook false positives, add 11 session-manager tests

- Fix post-edit-typecheck.js error filtering: use relative/absolute path
  matching instead of basename, preventing false positives when multiple
  files share the same name (e.g., src/utils.ts vs tests/utils.ts)
- Add writeSessionContent tests (create, overwrite, invalid path)
- Add appendSessionContent test (append to existing file)
- Add deleteSession tests (delete existing, non-existent)
- Add sessionExists tests (file, non-existent, directory)
- Add getSessionStats empty content edge case
- Add post-edit-typecheck stdout passthrough test
- Total: 391 → 402 tests, all passing

tests/hooks/hooks.test.js

@@ -639,6 +639,18 @@ async function runTests() {
     cleanupTestDir(testDir);
   })) passed++; else failed++;
 
+  if (await asyncTest('passes through stdin data on stdout (post-edit-typecheck)', async () => {
+    const testDir = createTestDir();
+    const testFile = path.join(testDir, 'test.ts');
+    fs.writeFileSync(testFile, 'const x: number = 1;');
+
+    const stdinJson = JSON.stringify({ tool_input: { file_path: testFile } });
+    const result = await runScript(path.join(scriptsDir, 'post-edit-typecheck.js'), stdinJson);
+    assert.strictEqual(result.code, 0);
+    assert.ok(result.stdout.includes('tool_input'), 'Should pass through stdin data on stdout');
+    cleanupTestDir(testDir);
+  })) passed++; else failed++;
+
   // session-end.js extractSessionSummary tests
   console.log('\nsession-end.js (extractSessionSummary):');