feat: show expandable tool call details in chat activity panel

Thread toolArguments from the sidecar through shared contracts, main-process pipeline, and into the renderer. Add ToolCallDetailPanel with inline summaries (command, path, pattern, etc.) and expandable argument details for every tool-call event in the activity timeline.

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

src/renderer/components/chat/ToolCallDetailPanel.tsx

@@ -0,0 +1,89 @@
+import { useState } from 'react';
+import { ChevronRight } from 'lucide-react';
+
+import {
+  formatToolCallSummary,
+  formatToolArgumentValue,
+  getDisplayableArguments,
+} from '@renderer/lib/toolCallSummary';
+
+export interface ToolCallDetailPanelProps {
+  toolName?: string;
+  toolArguments?: Record<string, unknown>;
+}
+
+export function ToolCallDetailPanel({ toolName, toolArguments }: ToolCallDetailPanelProps) {
+  const [expanded, setExpanded] = useState(false);
+
+  const summary = formatToolCallSummary(toolName, toolArguments);
+  const displayArgs = getDisplayableArguments(toolArguments);
+  const hasExpandableContent = displayArgs.length > 0;
+
+  if (!summary && !hasExpandableContent) return null;
+
+  return (
+    <div className="mt-0.5">
+      {/* Inline summary — always visible when summary exists */}
+      <button
+        type="button"
+        className={`group flex max-w-full items-start gap-1 text-left text-[11px] leading-snug ${
+          hasExpandableContent
+            ? 'cursor-pointer hover:text-[var(--color-text-secondary)]'
+            : 'cursor-default'
+        }`}
+        onClick={hasExpandableContent ? () => setExpanded((prev) => !prev) : undefined}
+        aria-expanded={hasExpandableContent ? expanded : undefined}
+        aria-label={hasExpandableContent ? `Toggle ${toolName} arguments` : undefined}
+        tabIndex={hasExpandableContent ? 0 : -1}
+        onKeyDown={hasExpandableContent
+          ? (e) => { if (e.key === ' ') { e.preventDefault(); setExpanded((prev) => !prev); } }
+          : undefined}
+      >
+        {hasExpandableContent && (
+          <ChevronRight
+            className={`mt-px size-2.5 shrink-0 text-[var(--color-text-muted)] transition-transform duration-150 ${
+              expanded ? 'rotate-90' : ''
+            }`}
+          />
+        )}
+        {summary && (
+          <span className="min-w-0 truncate font-mono text-[var(--color-text-muted)] group-hover:text-[var(--color-text-secondary)]">
+            {summary}
+          </span>
+        )}
+      </button>
+
+      {/* Expanded argument list */}
+      {expanded && hasExpandableContent && (
+        <div className="mt-1 overflow-hidden rounded-md border border-[var(--color-border-subtle)] bg-[var(--color-surface-0)]/80">
+          <div className="max-h-48 overflow-auto">
+            {displayArgs.map(([key, value]) => {
+              const formatted = formatToolArgumentValue(value);
+              const isMultiline = formatted.includes('\n') || formatted.length > 120;
+
+              return (
+                <div
+                  key={key}
+                  className="border-b border-[var(--color-border-subtle)] px-2 py-1 last:border-b-0"
+                >
+                  <span className="text-[10px] font-semibold tracking-wide text-[var(--color-accent-purple)]">
+                    {key}
+                  </span>
+                  {isMultiline ? (
+                    <pre className="mt-0.5 max-h-32 overflow-auto whitespace-pre-wrap break-all font-mono text-[10px] leading-relaxed text-[var(--color-text-secondary)]">
+                      {formatted}
+                    </pre>
+                  ) : (
+                    <span className="ml-1.5 font-mono text-[10px] text-[var(--color-text-secondary)]">
+                      {formatted}
+                    </span>
+                  )}
+                </div>
+              );
+            })}
+          </div>
+        </div>
+      )}
+    </div>
+  );
+}

src/renderer/components/chat/TurnActivityPanel.tsx

@@ -15,6 +15,7 @@ import {
 
 import { useElapsedTimer } from '@renderer/hooks/useElapsedTimer';
 import { FileChangePreview } from '@renderer/components/chat/FileChangePreview';
+import { ToolCallDetailPanel } from '@renderer/components/chat/ToolCallDetailPanel';
 import { RunChangeSummaryCard } from '@renderer/components/chat/RunChangeSummaryCard';
 import { formatEventLabel, truncateContent, filterEventsByAgent, summarizeActivity, type ActivitySummary } from '@renderer/lib/runTimelineFormatting';
 import type { ChatMessageRecord } from '@shared/domain/session';
@@ -186,6 +187,11 @@ function ActivityTimelineEventRow({ event }: { event: RunTimelineEventRecord })
           </p>
         )}
 
+        {/* Tool call argument details */}
+        {event.kind === 'tool-call' && (
+          <ToolCallDetailPanel toolName={event.toolName} toolArguments={event.toolArguments} />
+        )}
+
         {/* File change preview for tool-call events */}
         {event.kind === 'tool-call' && event.fileChanges && event.fileChanges.length > 0 && (
           <div className="mt-1">