[FEATURE]:Replace Default Scrollbar with a Conversation Quick Navigation Bar Description #31633

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OpenCode currently relies on the standard browser vertical scrollbar for navigating long chat histories. This method provides no context about the content at different scroll positions, making it difficult and slow to locate specific messages, code blocks, or earlier turns in extended multi-turn conversations. This is a major friction point when working on complex, multi-step development tasks where referencing previous context is frequent. Proposed Solution Replace or augment the default scrollbar with a compact, context-aware conversation navigation bar along the right edge of the chat view. This bar will provide visual markers representing key points in the conversation, allowing users to jump directly to specific sections. Key Features: 1. Contextual Markers: ◦ Each user message and assistant response gets a clickable marker. ◦ Additional, distinct markers for structural elements like code blocks, error messages, or user-defined sections. 2. Visual & Interactive Feedback: ◦ Markers are positioned vertically to correspond with the scroll position of their target content. ◦ Hovering over a marker shows a tooltip preview of the message. ◦ The marker for the currently visible section is highlighted. 3. Instant Navigation: Clicking a marker smoothly scrolls the viewport to the corresponding conversation segment. 4. Non-Intrusive Design: The bar should be slim and unobtrusive, preserving maximum space for the main chat content. Benefits • Faster Context Switching: Users can jump directly to requirements, previous code versions, or error messages without aimless scrolling. • Reduced Cognitive Load: Visual markers provide an overview of the conversation's structure, making it easier to follow the flow of complex tasks. • Improved Workflow: Eliminates the frustration of losing context in long development sessions. Use Case Example When debugging a multi-part automation script over 30+ conversation turns, a user could: 1. Hover over markers to quickly identify the initial requirements. 2. Click directly to the section where a specific error was first reported. 3. Jump back to the latest solution without manually scrolling through dozens of messages. Implementation Notes This feature can be implemented as a progressive enhancement: 1. Keep the native scrollbar as a fallback, or hide it in favor of a custom container. 2. Use IntersectionObserver or scroll event listeners to track message visibility and update the active marker. 3. Position markers using the offsetTop of each message element to ensure they align correctly with the scroll position. 4. Use scrollIntoView() for smooth, animated scrolling to the target element. This change would significantly improve the usability of OpenCode for power users working on long, complex tasks.