fix: honor underscore-unused convention and make durability fsyncs cross-platform

- eslint: respect the repo's existing _-prefix convention for unused vars
- phase-one-blockers: derive projectRoot via import.meta.dirname so Windows
  checkouts stop producing C:\C:\... paths
- backup/release-evidence/cutover-orchestrator: skip POSIX-only directory
  fsync on win32 and fsync read-only handles through a writable handle

apps/api/src/cutover-orchestrator.ts

@@ -289,12 +289,15 @@ async function durableState(plan: CutoverPlan, state: CutoverState): Promise<voi
     await handle.close();
   }
   await rename(temporary, target);
+  if (process.platform !== 'win32') {
+    // directory fsync only exists on POSIX
     const directory = await open(plan.stateDir, constants.O_RDONLY);
     try {
       await directory.sync();
     } finally {
       await directory.close();
     }
+  }
 }
 
 function preparedState(plan: CutoverPlan): CutoverState {

apps/api/src/infrastructure/database/backup.ts

@@ -159,7 +159,8 @@ async function digestFileHandle(handle: FileHandle): Promise<string> {
 }
 
 async function syncFile(path: string): Promise<void> {
-  const handle = await open(path, 'r');
+  // Windows FlushFileBuffers requires a writable handle; POSIX allows fsync on 'r'.
+  const handle = await open(path, process.platform === 'win32' ? 'r+' : 'r');
   try {
     await handle.sync();
   } finally {
@@ -168,6 +169,7 @@ async function syncFile(path: string): Promise<void> {
 }
 
 async function syncDirectory(path: string): Promise<void> {
+  if (process.platform === 'win32') return; // directory fsync only exists on POSIX
   const handle = await open(path, 'r');
   try {
     await handle.sync();

apps/api/src/release-evidence.ts

@@ -254,12 +254,15 @@ export async function appendReleaseEvidence(
       await handle.close();
     }
     await rename(temporary, absolute);
+    if (process.platform !== 'win32') {
+      // directory fsync only exists on POSIX
       const directory = await open(parent, 'r');
       try {
         await directory.sync();
       } finally {
         await directory.close();
       }
+    }
     return Object.freeze(record);
   } finally {
     await lock.close();

eslint.config.js

@@ -30,6 +30,14 @@ export default defineConfig(
     },
     rules: {
       'no-undef': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        {
+          argsIgnorePattern: '^_',
+          varsIgnorePattern: '^_',
+          caughtErrorsIgnorePattern: '^_',
+        },
+      ],
     },
   },
 );

test/phase-one-blockers.test.js

@@ -14,7 +14,7 @@ import { RequestCoordinator } from '../public/state/request-coordinator.js'
 import { createApiClient } from '../public/infrastructure/api-client.js'
 import { createViewRouter } from '../public/router/view-router.js'
 
-const projectRoot = path.resolve(path.dirname(new URL(import.meta.url).pathname), '..')
+const projectRoot = path.resolve(import.meta.dirname, '..')
 
 async function files(instances = []) {
   const dir = await mkdtemp(path.join(tmpdir(), 'msa-blockers-'))