[Proposal][desktop-gpui] Startup Upload Health Check & Pre-Recording Bandwidth Diagnostics (follow-up to #73 / #3188) #3218

Following up on @richiemcilroy's feedback on #3188 (and #73) regarding the transition from legacy apps/desktop (Tauri) to the native GPUI app (apps/desktop-gpui), opening this issue first so we can align on the product behavior before writing any code.

Proposed Scope for apps/desktop-gpui

1. Startup Upload Connectivity & Storage Health Check (apps/desktop-gpui/src/upload.rs & diagnostics.rs)

   • Run a lightweight, non-blocking startup check using the existing authenticated client (preserving apply_env_headers / preview bypass headers) and verifying actual S3/storage write readiness rather than a no-op body discard.
   • Surface a subtle warning badge in main_window.rs if upload connectivity or storage reachability is degraded, with a one-click diagnostics detail view.

2. Pre-Recording Upload Speed Probe & Resolution Behavior (apps/desktop-gpui/src/recording.rs)

   • Execute a one-shot probe prior to recording start (cancelled immediately before clean_capture::prepare on all platforms including Linux, using Duration::saturating_sub / checked_sub).
   • Product Question for @richiemcilroy: For apps/desktop-gpui, would you prefer:
     • (Option A - Advisory Warning / Opt-in): Keep the user's selected capture resolution intact by default and show a non-intrusive recommendation banner when upload throughput is below threshold, or
     • (Option B - Automatic Instant-Mode Cap): Automatically cap resolution only for Instant Mode recordings (where real-time chunk upload matters) while leaving Studio Mode at full Resolution::Captured?

Happy to adjust the design to match your roadmap for apps/desktop-gpui before submitting a PR.