fix: resolve onboarding welcome template empty content bug (BUG-ONBOARD-001)

[ThisIs-Developer]

Overview

This PR resolves the critical onboarding bug BUG-ONBOARD-001, where first-time users see a blank editor and preview panel despite the "Welcome to Markdown" tab being successfully created.

Root Cause Analysis

1. PWA Cache Mismatch (Stale-While-Revalidate): The PWA service worker caches index.html using a stale-while-revalidate strategy. If a user receives the cached version of index.html from a previous release (which defines the template as <template id="default-markdown">) but loads the new script.js (which expects <script type="text/markdown" id="default-markdown"> and accesses its textContent), the resulting retrieval evaluates to "" since a <template> tag's contents reside inside its .content document fragment.
2. Brittle Fallback Check: Because the DOM element is found (non-null), the ternary operator selected the textContent branch. Evaluating "".trim() yielded an empty string "" and completely bypassed the hardcoded welcome markdown fallback.

Remediation Details

• Resilient Template Extraction: Updated script.js to dynamically inspect the template element. It now safely extracts text content from both modern <script type="text/markdown"> and older cached <template> tags.
• Robust Fallback: Switched the ternary assignment to a logical OR (||) condition. This guarantees that if retrieved text is empty or missing, the application automatically falls back to the hardcoded welcome markdown string rather than hydrating an empty editor.
• Desktop Application Sync: Rebuilt the Neutralino desktop resources (node prepare.js) to sync the script.js changes to desktop-app/resources/js/script.js and update the offline-first resources/index.html.

Verification & Testing

1. Hydration Verification:
   • Simulated standard <script> tag: PASS (retrieved full welcome markdown)
   • Simulated stale cached <template> tag: PASS (retrieved full welcome markdown)
   • Simulated null/missing element: PASS (fell back to hardcoded default)
   • Simulated empty element: PASS (fell back to hardcoded default)
2. Web Regression Testing: Verified in Incognito mode and with cleared localStorage that the editor and preview hydrate perfectly. Existing saved tabs continue to load exactly as before.
3. Desktop Regression Testing: Verified that fresh Neutralino client launches successfully hydrate the editor and preview.

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Project	Deployment	Actions	Updated (UTC)
markdown-viwer	Ready	Preview, Comment	May 31, 2026 7:37pm

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