feat(ai-chat): tag subagent tool events with parentToolId, style nested rows

Pairs with the phoenix-pro inline-subagent-steps renderer. The backend
now looks up the dispatching Agent's toolCounter from
_toolUseIdToCounter[message.parent_tool_use_id] and includes it on
both aiProgress and aiToolInfo events so the browser knows where to
render each step. Styling adds .ai-subagent-steps (left border +
indent for the nested block) and .ai-subagent-step / -icon / -label
(compact one-line rows with the secondary text size and ellipsis
truncation).

Author: abose

src-node/claude-code-agent.js

@@ -1628,23 +1628,27 @@ async function _runQuery(requestId, prompt, projectPath, model, signal, locale,
             if (message.type === "assistant" &&
                     message.parent_tool_use_id &&
                     message.message && Array.isArray(message.message.content)) {
+                const parentToolId = _toolUseIdToCounter[message.parent_tool_use_id];
                 for (const block of message.message.content) {
                     if (block && block.type === "tool_use") {
                         toolCounter++;
                         if (block.id) {
                             _toolUseIdToCounter[block.id] = toolCounter;
                         }
-                        _log("Subagent tool:", block.name, "#" + toolCounter);
+                        _log("Subagent tool:", block.name, "#" + toolCounter,
+                            "parent=#" + (parentToolId !== undefined ? parentToolId : "?"));
                         nodeConnector.triggerPeer("aiProgress", {
                             requestId: requestId,
                             toolName: block.name,
                             toolId: toolCounter,
+                            parentToolId: parentToolId,
                             phase: "tool_use"
                         });
                         nodeConnector.triggerPeer("aiToolInfo", {
                             requestId: requestId,
                             toolName: block.name,
                             toolId: toolCounter,
+                            parentToolId: parentToolId,
                             toolInput: block.input || {}
                         });
                     }

src/styles/Extn-AIChatPanel.less

@@ -1126,6 +1126,39 @@
     }
 }
 
+/* ── Subagent step rows ──────────────────────────────────────────────
+   Compact one-line entries inside an Agent dispatcher card showing
+   what the subagent is doing (Read foo.json, Searched: *.md, etc).
+   Indented with a left border so the nesting reads clearly. */
+.ai-subagent-steps {
+    margin-top: 4px;
+    padding-left: 8px;
+    border-left: 2px solid fade(@project-panel-text-2, 25%);
+}
+
+.ai-subagent-step {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 2px 0;
+    font-size: @ai-text-secondary;
+}
+
+.ai-subagent-step-icon {
+    width: 14px;
+    text-align: center;
+    flex-shrink: 0;
+    font-size: @ai-text-secondary;
+}
+
+.ai-subagent-step-label {
+    color: @project-panel-text-2;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    min-width: 0;
+}
+
 @keyframes ai-spin {
     to { transform: rotate(360deg); }
 }