fix: auth scheduler env vars, concurrency and browser stability

docs/plans/FixSchedulerConcurrencyAndBrowser.md

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+# Execution Plan: Fix Scheduler Concurrency and Browser Stability
+
+## Context
+The application is experiencing two related issues with the Instagram authentication scheduler:
+1.  **Console Spam**: "Auth renewal already in progress" is logged repeatedly. This indicates the scheduler is triggering new renewal attempts while a previous one is still active (or perceived as active). This is likely caused by an invalid or extremely short interval configuration (e.g., `NaN` resulting from parsing failure).
+2.  **Browser Instability**: "Target page, context or browser has been closed" errors. This occurs when the scheduler attempts to use a cached Playwright browser instance that has crashed or disconnected.
+
+## Goal
+Ensure the authentication scheduler runs reliably at the configured interval without overlapping executions, and make the browser instance management robust against crashes.
+
+## Exception to workflow
+Do not create a dedicated branch. It's a fix on a new feature.
+
+## Proposed Solution
+
+### Story 1: Fix Scheduler Configuration and Resource Cleanup
+**Objective**: Prevent rapid-fire execution of the scheduler and ensure browser resources are cleaned up properly even when errors occur.
+
+**Changes**:
+1.  **Validate Configuration**: In `src/lib/server/scheduler.ts`, update `getConfig()` to strictly validate `intervalMinutes`.
+    *   Handle `NaN` (parsing errors).
+    *   Enforce a minimum interval (e.g., 15 minutes) to prevent spamming.
+    *   Default to 720 minutes if invalid.
+2.  **Improve Resource Management**: Refactor `renewInstagramAuth` to ensure `page` and `context` are closed in a `finally` block (or nested `try/finally`), preventing resource leaks if an error occurs during the renewal process.
+
+**Verification**:
+*   Set `AUTH_SCHEDULER_INTERVAL_MINUTES` to an invalid value (e.g., "abc") and verify it defaults to 720.
+*   Verify that `setInterval` is called with a valid duration.
+
+### Story 2: Robust Browser Lifecycle Management
+**Objective**: Ensure the application automatically recovers from browser crashes by detecting disconnected instances.
+
+**Changes**:
+1.  **Check Connection Status**: In `src/lib/server/browser.ts`, update `getBrowser()` to check `browser.isConnected()`.
+2.  **Auto-Recovery**: If the cached browser instance is not connected:
+    *   Log a warning.
+    *   Attempt to close the dead instance (swallowing errors).
+    *   Re-initialize a new browser instance.
+
+**Verification**:
+*   Simulate a browser crash (e.g., by manually killing the chrome process if possible, or mocking `isConnected` to return false).
+*   Verify that the next call to `getBrowser()` creates a new instance instead of throwing.
+
+## Implementation Details
+
+### `src/lib/server/scheduler.ts`
+```typescript
+function getConfig(): SchedulerConfig {
+    const enabled = env.AUTH_SCHEDULER_ENABLED === 'true';
+    let intervalMinutes = parseInt(env.AUTH_SCHEDULER_INTERVAL_MINUTES || '720', 10);
+
+    if (isNaN(intervalMinutes) || intervalMinutes < 15) {
+        console.warn(`[Scheduler] Invalid or too short interval '${env.AUTH_SCHEDULER_INTERVAL_MINUTES}'. Defaulting to 720 minutes.`);
+        intervalMinutes = 720;
+    }
+
+    return { enabled, intervalMinutes };
+}
+
+// In renewInstagramAuth:
+let context = null;
+let page = null;
+try {
+    // ... setup ...
+    context = await browser.newContext(...);
+    page = await context.newPage();
+    // ... logic ...
+} catch (e) {
+    // ... error handling ...
+} finally {
+    if (page) await page.close().catch(() => {});
+    if (context) await context.close().catch(() => {});
+    state.isRenewing = false;
+}
+```
+
+### `src/lib/server/browser.ts`
+```typescript
+export async function getBrowser(): Promise<Browser> {
+    if (!browser || !browser.isConnected()) {
+        if (browser) {
+            console.warn('Browser is disconnected. Re-initializing...');
+            try { await browser.close(); } catch (e) { /* ignore */ }
+        }
+        return initializeBrowser();
+    }
+    return browser;
+}
+```