Add on-demand detailed logs with button and LLM summaries for background sessions

[Copilot]

Session summaries now show a button to load detailed logs on demand instead of auto-scrolling. Background sessions without PR data use VS Code's LLM API to generate summaries from logs.

Changes

Content Loading

• Summary loads first with button only - detailed logs hidden initially
• Button click triggers state change and content refresh via onDidChangeChatSessionOptions
• Second load includes full session history with tool calls and interactions

LLM Integration

• Uses vscode.lm.selectChatModels with GPT-4o, falls back to any Copilot model
• Parses session logs to extract tool calls and agent output
• Generates 1-2 sentence user-focused summaries (max 300 chars)

State Management

// Track which sessions show full logs
private readonly sessionShowFullLogsMap = new ResourceMap<boolean>();

// Toggle and refresh
showFullLogs(sessionResourceUri: string) {
  this.sessionShowFullLogsMap.set(resource, true);
  this._onDidChangeChatSessionOptions.fire({ resource, updates: [] });
}

Conditional History Building

buildSessionHistory(..., options?: { 
  includeSummary?: boolean;
  includeDetailedLogs?: boolean 
})

// Early return if summary-only
if (options?.includeSummary && !options?.includeDetailedLogs) {
  return [summaryTurn];
}

Example Output

Cloud Session (with PR)

## 📋 Session Summary

**Goal:** Add authentication to API endpoints
✅ **Status:** Completed
**What it does:** Implements JWT-based authentication middleware...
**Changes Made:** 8 files modified (+247 / -12 lines)

[View Session Log] ← Button

Background Session (LLM-generated)

## 📋 Session Summary

**Goal:** Fix database connection issues
✅ **Status:** Completed
**What it does:** Updated connection pool settings and added retry logic to handle transient failures.

[View Session Log] ← Button

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