[FEATURE] VS Code extension: support the SCM ✨ "Generate Commit Message" button

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

VS Code's Source Control panel renders a ✨ (sparkle) icon in the commit message input box — its built-in Generate Commit Message affordance. Per VS Code's docs: "To help you write a commit message, select the sparkle icon in the commit message input box to use AI to generate the message based on your staged changes." (Staging and committing changes)

This icon is driven by the scm/inputBox menu contribution point: when an installed extension contributes a command to that menu, VS Code surfaces the action on the input box; the command is invoked with the repository and writes its result back via SourceControlInputBox.value.

The Claude Code VS Code extension does not register any scm/inputBox command, so for users who have Claude Code installed (and no other provider such as GitHub Copilot), clicking ✨ produces nothing. Claude already generates high-quality commit messages from the CLI, but that capability is not exposed where developers expect it in the VS Code Git panel.

Proposed Solution

Have the Claude Code VS Code extension register a commit-message provider for the SCM input box:

1. The extension's manifest contributes a command to the scm/inputBox menu (e.g. claude-code.git.generateCommitMessage).
2. Invoking ✨ collects the staged diff from the active repository, asks Claude to generate a commit message, and sets repository.inputBox.value with the result.
3. The generated message honors the user's existing commit-message conventions/attribution settings.

Alternative Solutions

• Continue generating commit messages via the CLI (/commit-style workflows) and copy/paste — the current workaround, but it bypasses the native ✨ affordance.
• Install GitHub Copilot solely to populate the ✨ button — undesirable for users who have standardized on Claude Code.

Priority

Medium - Would be very helpful

Feature Category

Other (IDE / VS Code extension)

Use Case Example

1. I stage changes in a repo inside VS Code with the Claude Code extension installed.
2. I click the ✨ icon in the Source Control commit message box.
3. Claude reads my staged diff and populates the commit message input.
4. I review/edit and commit — without leaving the Git panel or switching to the terminal.

Additional Context

Relevant documentation / API surface

• Sparkle behavior: Staging and committing changes — describes the ✨ AI commit-message generation.
• Contribution point: scm/inputBox menu — Source Control API guide and Contribution Points reference. Origin proposal: microsoft/vscode#195474 — SCM Input: scm/inputBox menu contribution proposal.
• Setting the message: SourceControl.inputBox → SourceControlInputBox.value (string, get/set) — [VS Code API reference] (https://code.visualstudio.com/api/references/vscode-api).
• Prior art: GitHub Copilot Chat contributes a scm/inputBox command for the same sparkle slot — a working model for how a Claude Code provider would integrate.

Environment

• VS Code with the Claude Code extension
• Extension version: 2.1.190