Desktop sessions were failing before the actual fetch because Anthropic's domain preflight can be unreachable on restricted networks, and the next runtime path was missing turndown for HTML-to-Markdown conversion.
This change defaults desktop sessions to skip the preflight unless the user explicitly overrides it, exposes that behavior as a desktop General setting, seeds new settings JSON with the desktop-safe default, and adds regression coverage for both the runtime default and the UI toggle. It also adds the missing turndown dependency so successful fetches can continue through HTML reduction instead of failing at module resolution.
Constraint: Desktop must keep an escape hatch for users who want upstream preflight restored explicitly
Rejected: Force skipWebFetchPreflight globally for every session | would silently change CLI and non-desktop behavior
Rejected: UI-only toggle without runtime default | existing desktop users would still fail until they manually opened settings
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep desktop-specific WebFetch behavior scoped to desktop session detection and explicit user settings; do not broaden it to general CLI flows without separate validation
Tested: bun test src/tools/WebFetchTool/utils.test.ts; cd desktop && bun run lint; cd desktop && bunx vitest run src/__tests__/generalSettings.test.tsx; runtime import verification for turndown via node
Not-tested: End-to-end desktop packaging smoke test against a freshly built DMG/app bundle
