[FEATURE] Enable spellcheck in VSCode extension input (blocked on microsoft/vscode#214367)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

While this feature has been requested several times (see #16833, #40888 — both closed and locked), it is additionally blocked upstream in VS Code itself. The spellcheck="true" HTML attribute has no effect in webview iframes — Electron's spellcheck service only wires into the top-level webContents, not sandboxed frames. I confirmed this by patching the Claude Code webview bundle locally.

The root cause is tracked at microsoft/vscode#214367 (<textarea> in webviews don't support spellcheck). It was closed by the VS Code bot in June 2025 for not reaching 20 upvotes within 60 days — not as wontfix. It needs 17 more upvotes to hit the 20-upvote threshold and re-enter backlog candidacy.

Anthropic commenting or upvoting that issue as a major extension publisher would likely get it re-triaged. Until VS Code exposes spellcheck support in its webview API, this cannot be fixed at the extension level.

Proposed Solution

Upvote and/or comment on microsoft/vscode#214367 as a first-party publisher to signal demand and get it re-triaged. Once VS Code exposes spellcheck support in the webview API, enabling it in the Claude Code extension input should be straightforward.

Alternative Solutions

None — the HTML attribute patch does not work due to the sandboxed iframe architecture.

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Prompt intent: A misspelling can silently alter the meaning of a prompt — "asses the code" vs "assess the code" being a trivial but illustrative example. Claude handles many typos gracefully, but ambiguous misspellings can produce subtly wrong output with no indication of why.

Prompt reuse and sharing: Prompts are increasingly treated as reusable artifacts — saved, shared, and published. Typos in shared prompts look unprofessional and reduce trust in the output.

Training data quality: If user prompts factor into future training, misspellings in training data could reinforce non-standard usage over time. Spellcheck is a low-cost quality gate at the point of input.

Additional Context

Tested on: macOS, Claude Code VSCode extension v2.1.179.

Confirmed that setting spellcheck="true" on the input element in webview/index.js (currently hardcoded to "false" in two places) has no effect — the sandboxed iframe architecture prevents Electron's spellcheck service from reaching webview content regardless of the HTML attribute.

The fix is entirely dependent on VS Code exposing spellcheck in its WebviewOptions API (microsoft/vscode#214367). Once that lands, the Claude Code change would be a one-line patch.