docs: document VS Code extension source layout

The PR already includes the extension host and webview source under packages/vscode-extension, but reviewers need an entry point that explains which directories are source, which files are generated output, and why source is excluded from the VSIX package.

Constraint: Source should remain reviewable in the repository while the VSIX continues to ship compiled assets only.

Rejected: Rely on root feature docs only | they describe architecture but are not colocated with the extension source tree.

Confidence: high

Scope-risk: narrow

Directive: Keep this README aligned with .vscodeignore whenever the packaging boundary changes.

Tested: git diff --check

Not-tested: Re-running VS Code extension smoke tests for this docs-only change

Author: unraid

packages/vscode-extension/README.md

@@ -0,0 +1,76 @@
+# CCB VS Code Extension
+
+This directory contains the full source for the VS Code extension.
+
+The extension is committed to the repository for review and development, while the packaged VSIX intentionally ships only compiled assets and required metadata.
+
+## Source Layout
+
+| Path | Purpose |
+| --- | --- |
+| `src/` | VS Code extension host code. It starts and manages the ACP agent process, registers commands, bridges editor state, and owns extension lifecycle. |
+| `webview/` | React webview source. It renders chat, slash commands, permissions, model/mode selectors, plans, and tool call cards. |
+| `webview/lib/` | Shared webview protocol, ACP-facing types, slash-command parsing, and thread reducer logic. |
+| `scripts/` | Local install and smoke-test scripts. |
+| `resources/` | VS Code extension resources, including the activity bar icon. |
+| `dist/` | Build output generated by `bun run build`; this is what the VSIX loads at runtime. |
+
+## Development Install
+
+From the repository root:
+
+```powershell
+bun run build
+cd packages\vscode-extension
+bun run install-local:win
+```
+
+On macOS/Linux:
+
+```bash
+bun run build
+cd packages/vscode-extension
+bun run install-local
+```
+
+Fully quit VS Code and reopen it after installation.
+
+## Build and Smoke Test
+
+```powershell
+cd packages\vscode-extension
+bun run test:all
+```
+
+The smoke test covers extension manifest loading, ACP startup, slash-command metadata, and `/mcp tools claude-in-chrome`.
+
+## Packaging Boundary
+
+`packages/vscode-extension/.vscodeignore` excludes source and test files from the VSIX:
+
+```text
+src/
+webview/
+scripts/
+node_modules/
+tsconfig.json
+esbuild.config.mjs
+*.map
+```
+
+Before publishing, verify package contents:
+
+```powershell
+npx @vscode/vsce ls --no-dependencies
+```
+
+Expected packaged files:
+
+```text
+package.json
+resources/icon.svg
+dist/webview.js
+dist/extension.js
+```
+
+Do not remove the source exclusions unless the release policy changes and the VSIX contents are reviewed again.