feat: sidebar sessions panel with auto-resume and session history browsing

[cy2311]

Problem

Currently there is no way to see all conversation sessions in a persistent sidebar panel. The only way to switch between sessions is Ctrl+R (session picker popup) or codewhale run --continue at startup.

This creates friction:

• Users have to remember to use Ctrl+R to find old conversations
• There is no visual overview of all sessions (titles, timestamps, last message preview)
• Starting CodeWhale fresh loses the previous session context unless the user explicitly remembers --continue
• No intuitive way to browse, search, or manage past conversations

Proposed Solution

Add a Sessions panel to the sidebar (alongside existing Work / Tasks / Agents / Context panels), similar to how VS Code / Cursor / Codex show a chat history list on the left side.

Design

1. Sidebar panel: A new SidebarFocus::Sessions variant that renders a scrollable list of all past sessions, each showing:

   • Session title or first prompt
   • Timestamp (relative: "2h ago", "yesterday", "Jun 5")
   • Last message preview (truncated to one line)
   • Status indicator (active / archived)

2. Interaction:

   • Click/Enter on a session → switches to that session (loads history into the transcript)
   • Delete key → option to archive/remove a session
   • Right-click / context menu → rename, export, delete

3. Auto-resume:

   • On startup, default to the most recent session instead of a blank state
   • Or show the Sessions panel by default with the latest session pre-selected

Keybindings (suggested)

• Alt+S or similar to focus the Sessions sidebar panel
• Ctrl+R stays as an alternative quick-switch

Alternatives Considered

1. Keep Ctrl+R as the only session switching mechanism — current state, confusing for new users
2. Show sessions only at startup in a picker — one-time choice, doesn't help during a session
3. Auto-save and auto-restore the last session without showing history — solves persistence but not browsing

Additional Context

• Current SidebarFocus enum has: Auto, Work, Tasks, Agents, Context, Hidden — no Sessions variant
• Session data is already persisted to disk (SQLite store in crates/tui/src/session_manager.rs)
• Ctrl+R already opens a session picker popup, suggesting the session listing infrastructure exists
• Main gap is a persistent sidebar panel + startup auto-resume

[github-actions]

Thanks @cy2311 for the report.

This issue is staying open for maintainer triage. CodeWhale gets better because people bring us real edge cases from real machines, providers, regions, and workflows.

If you can add a reproduction, logs, version output, screenshots, or the provider/model involved, that makes it much easier for us to verify and harvest the fix. Maintainers may comment /lgtmi to mark recurring issue reporters as approved so this intake note is skipped next time.

[Hmbown]

this is a cool idea! are you able to sketch out a bit of what you're imagining here? I think I understand but it's always helpful when I can get a visual :) @cy2311