feat: add token count column to diagnostics session files tab

- Add tokens? field to SessionFileDetails interface
- Populate tokens from cache in getSessionFileDetailsFromCache() and updateCacheWithSessionDetails()
- Add Tokens column in the diagnostics session table with compact K/M formatting
- Add Total Tokens summary card to the session files summary row
- Tooltip shows exact token count on hover

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: rajbos

vscode-extension/src/extension.ts

@@ -3144,6 +3144,7 @@ class CopilotTokenTracker implements vscode.Disposable {
 			size: cached.size || stat.size,
 			modified: stat.mtime.toISOString(),
 			interactions: cached.interactions,
+			tokens: cached.tokens || 0,
 			contextReferences: cached.usageAnalysis.contextReferences,
 			firstInteraction: cached.firstInteraction || null,
 			lastInteraction: lastInteraction,
@@ -3170,6 +3171,9 @@ class CopilotTokenTracker implements vscode.Disposable {
 		// Get existing cache entry if available
 		const existingCache = this.getCachedSessionData(sessionFile);
 
+		// Enrich details with token count from existing cache (populated by main stats calculation)
+		details.tokens = existingCache?.tokens || 0;
+
 		// Create or update cache entry
 		const cacheEntry: SessionFileCache = {
 			tokens: existingCache?.tokens || 0,

vscode-extension/src/types.ts

@@ -314,6 +314,7 @@ export interface SessionFileDetails {
   size: number;
   modified: string;
   interactions: number;
+  tokens?: number; // estimated token count for the session
   contextReferences: ContextReferenceUsage;
   firstInteraction: string | null;
   lastInteraction: string | null;

vscode-extension/src/webview/diagnostics/main.ts

@@ -24,6 +24,7 @@ type SessionFileDetails = {
   size: number;
   modified: string;
   interactions: number;
+  tokens?: number;
   contextReferences: ContextReferenceUsage;
   firstInteraction: string | null;
   lastInteraction: string | null;
@@ -188,6 +189,14 @@ function sanitizeNumber(value: number | undefined | null): string {
   return Math.floor(n).toString();
 }
 
+function formatTokenCount(value: number | undefined | null): string {
+  const n = Number(value ?? 0);
+  if (!Number.isFinite(n) || n === 0) { return "0"; }
+  if (n >= 1_000_000) { return `${(n / 1_000_000).toFixed(1)}M`; }
+  if (n >= 1_000) { return `${(n / 1_000).toFixed(1)}K`; }
+  return Math.floor(n).toString();
+}
+
 /**
  * Build a DOM element showing all candidate paths the extension considers,
  * with their existence status. Helps users understand why data may be missing.
@@ -509,6 +518,10 @@ function renderSessionTable(
     (sum, sf) => sum + Number(sf.interactions || 0),
     0,
   );
+  const totalTokens = filteredFiles.reduce(
+    (sum, sf) => sum + Number(sf.tokens || 0),
+    0,
+  );
   const totalContextRefs = filteredFiles.reduce(
     (sum, sf) => sum + getTotalContextRefs(sf.contextReferences),
     0,
@@ -581,6 +594,10 @@ function renderSessionTable(
 				<div class="summary-label">💬 Interactions</div>
 				<div class="summary-value">${totalInteractions}</div>
 			</div>
+			<div class="summary-card">
+				<div class="summary-label">🪙 Tokens</div>
+				<div class="summary-value" title="${totalTokens.toLocaleString()} tokens">${formatTokenCount(totalTokens)}</div>
+			</div>
 			<div class="summary-card">
 				<div class="summary-label">🔗 Context References</div>
 				<div class="summary-value">${safeText(totalContextRefs)}</div>
@@ -618,6 +635,7 @@ function renderSessionTable(
 						<th>Title</th>
 						<th>Repository</th>
 						<th>Size</th>
+						<th>Tokens</th>
 						<th>Interactions</th>
 						<th>Context Refs</th>
 						<th class="sortable" data-sort="lastInteraction">Last Interaction${getSortIndicator("lastInteraction")}</th>
@@ -636,6 +654,7 @@ function renderSessionTable(
 							</td>
 							<td class="repository-cell" title="${sf.repository ? escapeHtml(sf.repository) : "No repository detected"}">${sf.repository ? escapeHtml(getRepoDisplayName(sf.repository)) : '<span style="color: #666;">—</span>'}</td>
 							<td>${formatFileSize(sf.size)}</td>
+							<td title="${Number(sf.tokens || 0).toLocaleString()} tokens">${formatTokenCount(sf.tokens)}</td>
 							<td>${sanitizeNumber(sf.interactions)}</td>
 							<td title="${escapeHtml(getContextRefsSummary(sf.contextReferences))}">${sanitizeNumber(getTotalContextRefs(sf.contextReferences))}</td>
 							<td>${formatDate(sf.lastInteraction)}</td>