Feature: Tool window toolbar with session history

[bommerts]

Summary

Add a toolbar to the Copilot CLI embedded terminal tool window with buttons for viewing session history, starting a new session, and (eventually) deleting sessions. This mirrors the toolbar that VS's native Copilot Chat window already has.

Motivation

VS's native Copilot Chat has three toolbar buttons in the upper-right corner:

1. Circular arrow -- "View chat history"
2. Speech bubble with green + overlay -- "Create new thread"
3. Hamburger lines with red X overlay -- "Delete thread"

The Copilot CLI tool window currently has no toolbar at all. Adding one would let users resume previous CLI sessions without having to manually run copilot --resume, and it brings the UX closer to what VS users already expect from the native Copilot Chat.

How it could work

Copilot CLI stores all sessions in ~/.copilot/session-store.db (SQLite). Each session has a cwd (working directory) and repository field, so we can filter sessions to only show ones relevant to the current VS project.

View session history (button 1)

• Read session-store.db in read-only mode
• Filter sessions by the current workspace path
• Show a VS-themed picker dialog listing sessions with summary and date
• Resume the selected session with copilot --resume=<session-id>
• If no sessions exist for the workspace, show "No previous sessions for this project"

New session (button 2)

• Restart the terminal with a fresh copilot (no --resume flag)
• Same as current restart behavior, just exposed as a toolbar button

Delete session (button 3, future)

• Could be added later. Deleting from Copilot CLI's session store needs investigation.

Implementation notes

• Toolbar defined in .vsct with KnownMonikers icons (theme-aware, no custom bitmaps)
• KnownMonikers.History for the circular arrow icon
• Toolbar associated with TerminalToolWindow via the ToolBar property
• Session picker uses Microsoft.VisualStudio.PlatformUI.DialogWindow for VS-native look
• Microsoft.Data.Sqlite NuGet package for lightweight read-only DB access
• Gracefully handles missing DB, locked DB, and empty results

Questions

• Is adding Microsoft.Data.Sqlite as a dependency acceptable?
• Any preference on the session picker dialog style?

Volunteering to implement

I would like to implement this and open a PR. Builds on the embedded terminal from PR #7 and the native terminal refactor in PR #8.

[bommerts]

Starting on this. Planned approach:

PR 1 (this PR):

• Toolbar on TerminalToolWindow defined in .vsct, two buttons:
  • View session history — KnownMonikers.History
  • New session — KnownMonikers.NewItem
• Session picker: DialogWindow-based, lists sessions with summary + relative timestamp + turn count, sorted by updated_at DESC, Enter to resume.
• Read ~/.copilot/session-store.db via Microsoft.Data.Sqlite opened Mode=ReadOnly (won't contend with the live CLI's WAL writer).
• Filter by current workspace: cwd exact match OR cwd is a descendant of the workspace root, normalized + case-insensitive on Windows.
• Resume by relaunching the terminal with copilot --resume=<sessionId> (verified against CLI v1.0.32 — works as a startup flag in a fresh ConPTY).
• TerminalSessionService.RestartSession(workspaceFolder, resumeSessionId = null) — small, additive surface change.
• Schema is internal CLI state, so all DB access is wrapped in try/catch with graceful degradation ("Session history unavailable").
• SQLite read on a background thread, marshal results to UI via JoinableTaskFactory.

PR 2 (follow-up):

• Delete session button (KnownMonikers.DeleteListItem) after a quick spike on the CLI's session-store write semantics to confirm we won't corrupt anything.

Notes:

• New native dep (Microsoft.Data.Sqlite → e_sqlite3.dll) — will verify VSIX packaging + AppDomain native-DLL load before opening the PR, and document it in the PR description.
• Considering a third button later for --continue (resume most recent, no picker) since the CLI exposes it as a first-class flag — happy to defer / drop based on your preference.