[FEATURE] Track viewed vs unviewed state for completed sessions in Agent View

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When running many background sessions in parallel, the Completed section fills up quickly. With a long Completed list, there is no way to tell at a glance which sessions have already been opened and read, and which still need attention.

This is most noticeable for sessions whose deliverable is information rather than a PR — analysis, investigation, summarization, comparison, design notes, and similar. For these, the only way to get the result is to open the session and read it. There is no PR status indicator to lean on, and the Row Summary describes what the session was about but does not reflect whether I have actually opened it. A session I read this morning and a session that just finished look identical in the list.

The result is that I cannot reliably pick up where I left off across a batch of completed sessions, and I end up opening every one in turn just to check.

Proposed Solution

Track whether the user has opened or peeked at a session since it transitioned out of Working (Completed, Failed, or Stopped), and surface this as a visual marker in the Agent View list.

Concretely:

• An "unviewed" indicator (dot, bold session name, or coloured badge) on any session that has reached a terminal state but has not been opened by the user since.
• Automatically clear the indicator once the user attaches to or peeks at the session.
• Optionally, a sub-grouping or filter under "Completed" to show only unviewed sessions, and a bulk "mark all as read" action.

The key property is that tracking should be passive — no extra action required at the moment a session finishes, because that is exactly when attention is moving to the next task.

Alternative Solutions

Workarounds I have tried:

• Relying on the Row Summary alone. Useful for getting a sense of what a session was about, but it does not change once the session is complete, so it cannot distinguish "already read" from "just finished".

• Pinning sessions with Ctrl+T and renaming with Ctrl+R as a manual "still need to review" marker. This requires action at the exact moment the session completes, which is when attention has already moved elsewhere, so in practice the marker rarely gets applied consistently.

• Keeping a mental list of what is running. Does not scale once several sessions are in flight in parallel.

None of these provide passive tracking, which is the core of the problem.

Priority

High - Significant impact on productivity

Feature Category

Interactive mode (TUI)

Use Case Example

1. I start several background sessions in parallel. Some are coding tasks that will end with a PR; others are tasks where the deliverable is purely information — for example "summarize the auth flow in module X", "compare approaches A and B for caching", "explain why test Y is failing". These will not open a PR; the only way to get the answer is to open the session and read it.
2. I step away for a while to work on other things.
3. When I return, all of them are in the Completed section, mixed with other completed sessions from earlier in the day or week that I have already reviewed.
4. From the list alone I cannot tell which information-only sessions I still need to open and read.
5. With this feature, the unread ones would carry an "unviewed" indicator. As I open each, the indicator clears. When the section is visually clean, I know I have not missed anything.

Additional Context

_No response_