[FEATURE]:Add toggle to disable editor context auto-attachment for multi-window isolation

[xiangkehan]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem:
The Editor Context Protocol automatically attaches the current editor file/selection to every prompt via WebSocket. This works well for a single opencode window, but breaks se
ssion isolation when running multiple opencode windows in parallel.

Concrete scenario:
I often run 2–3 opencode TUI windows side-by-side for different tasks:

• Window A: working on backend/api.ts
• Window B: working on frontend/page.tsx
• Window C: working on docs/README.md

Since all windows connect to the same VS Code instance via WebSocket, every window receives the same editor context (the file currently focused in VS Code). This means:

• Window A's prompts get polluted with frontend/page.tsx context when I'm actually asking about the backend
• Window B's prompts get polluted with backend/api.ts context when I'm working on the frontend
• The session context is no longer isolated per window

Root cause:
There is no way to disable editor context auto-attachment per window. The only workaround is uninstalling the VS Code extension entirely, which also breaks @mention file autoc
omplete.

Proposed solution:
Add a per-window toggle command in the TUI command palette (Ctrl+K) to enable/disable editor context auto-attachment. The state should be persisted in the local KV store (kv. json) per workspace/session.

Expected behavior:

• When enabled (default): current behavior — blue file label shows, selection auto-attached
• When disabled: no editor context injected, but WebSocket stays alive for @mention autocomplete
• Each opencode window has its own toggle state

Benefits:

1. Restores session isolation for multi-window workflows
2. Prevents token waste from irrelevant file context
3. Keeps editor integration alive for manual @mention when needed
4. Small, focused change with minimal surface area

Scope:

• packages/opencode/src/cli/cmd/tui/context/editor.ts
• packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
• Unit tests

I am willing to implement and submit a PR if the core team approves.

[xiangkehan]

Context / 背景补充
The auto-attach editor context feature was introduced in PR #24034 (feat(tui): support builtin protocol for handling context from editors, commit 98ea5b6, 2026-04-23) by @longster.
自动附加编辑器上下文的功能是在 PR #24034（feat(tui): support builtin protocol for handling context from editors，提交 98ea5b6，2026-04-23）中由 @longster 引入的。