[FEATURE]: Integrated Manual File Editing via VS Code native diff editor #9370

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

Note: This builds upon and resolves the needs mentioned in #2167 and expands the discussion in #8003 by providing a full edit-and-sync implementation.

Problem

Currently, OpenCode handles file diffs exclusively within the TUI. While this is efficient for quick approvals, it lacks the flexibility for granular manual adjustments before committing a change. Users often need to make small corrections to the AI's output, a workflow that is currently cumbersome as it requires accepting the change first and then editing the file manually in a separate step.

Proposed Solution

I propose an integration that leverages the VS Code native diff editor when OpenCode is running in an integrated terminal. This provides a seamless "edit-and-approve" loop.
Key features of the implementation:

• Automatic Environment Detection: Recognition of VS Code via TERM_PROGRAM to toggle between TUI and IDE modes without manual configuration.
• Interactive Native Editing: 'edit' permission requests open a native VS Code diff tab, allowing users to modify the proposed changes directly in the IDE buffer.
• Stateful Synchronization: Real-time IDE connection tracking via SSE with robust reconnection logic to ensure the CLI and IDE stay in sync across terminal restarts.
• TUI Feedback: A minimalist UI state in the terminal (connection indicator + animated status) to provide clear feedback when the editor has focus.
• Reliability: Integrated line-ending normalization to ensure consistent file writes from external IDE buffers.

Verification Performed

• Validated with a full production build using Bun 1.3.5 (standalone binary test).
• Verified SSE stability through server restarts and IDE reconnections.
• Full type-safety check passed with turbo typecheck.

I have a functional prototype ready. I would like to open a PR for design review to ensure this aligns with the project's roadmap.