Webview panel creation is slow (300ms-1s+)

[SunYanbox]

Description

Both the one-shot PR creation and step-by-step PR webview panels take noticeably long to open (estimated 300ms to 1s+), hurting UX.

Root Causes

Looking at src/inputService.ts:

1. Large inline HTML payload — All four webview HTML templates (getWebviewHtml, getStepByStepHtml, getAddCommitHtml, getFinalizePrHtml) inline ~250 lines of CSS each. getWebviewHtml and getAddCommitHtml also render one DOM entry per changed file, generating substantial markup when there are many files.

2. Full diff renderer included upfront — The diff-view CSS, JS rendering logic, and inline styles are loaded even though most users won't expand diffs immediately.

3. VSCode Webview overhead — createWebviewPanel + setting panel.webview.html with a large string is inherently slow on the extension host. String concatenation via template literals blocks the JS thread.

4. Synchronous HTML generation — getWebviewHtml() runs synchronously with all files rendered eagerly. With 50+ changed files, the template literal alone takes non-trivial time.

Affected Code

• src/inputService.ts — all get*Html() functions (lines 26-528, 686-879, 881-1246, 1248-1412)
• Called via createWebviewPanel in collectInputs() (line 537) and collectStepByStepInputs() (line 1421)

Suggested Solution

1. Lazy-load diff CSS/JS — only inject diff-related styles and scripts when the user double-clicks to expand a file diff
2. Minimize inline CSS — extract shared styles or reduce duplication across the four templates
3. Virtualized file list — when there are 50+ files, render only the visible ones and use scroll event to render more
4. Async HTML generation — use setTimeout(0) to yield to the UI thread between template chunks
5. Consider a single shared webview with routing instead of 4 separate panel types, so the HTML/CSS is loaded once

No implementation required — design discussion only.