Feature request: sticky date and time indicator while scrolling chat history #164

Description

Add a sticky date and time indicator at the top of the conversation when scrolling through an OpenGUI session, similar to the floating date label in WhatsApp and other messaging apps.

Unlike a date-only label, the OpenGUI indicator should include both the date and the time, so users can tell when the currently visible part of the conversation took place.

Use Case

Long-running sessions can span several hours or days. When scrolling back through messages, tool calls, and responses, it is easy to lose track of when a particular interaction happened. A persistent temporal reference would make it easier to navigate the history and find earlier work.

Proposed Solution

• Show a small, unobtrusive pill centered at the top of the chat's scrollable area, below the session header.
• Display the date and time of the topmost visible message, for example Oct 7, 2026 · 14:32.
• Update the indicator as scrolling brings messages from a different time into view, in either direction.
• Keep it anchored within the conversation viewport, without changing the message layout or covering important controls.
• Use the user's locale and local time zone, including their preferred 12/24-hour format.
• Optionally fade the indicator after scrolling stops and show it again on the next scroll, following the familiar messaging-app pattern.
• If a message has no reliable timestamp, avoid inventing one; use the nearest timestamped visible message or hide the indicator.

Acceptance criteria

• Scrolling through a session spanning multiple dates updates both the date and time correctly.
• The indicator reflects the visible conversation position, not the current clock or the session's last activity time.
• It works when scrolling up and down, including after older history is loaded.
• It remains readable in light and dark themes and on narrow screens without intercepting scrolling or clicks.

Alternatives Considered

• Per-message timestamps: useful for precise details, but they add visual clutter and do not provide a consistent reference at the top of the viewport.
• Inline date separators only: useful for grouping messages by day, but they scroll out of view and do not show the time.

Additional Context

The inspiration is WhatsApp's floating date label at the top of a conversation while scrolling. For OpenGUI, the suggestion is to extend that pattern with the time as well.

Related: #124 requests dates and last-activity sorting in the session list. This proposal concerns temporal orientation inside an individual conversation.