refactor(term): add mutableRow to terminal api, use it for thinking_tokens

frontend/packages/agent/src/app.js

@@ -1886,11 +1886,12 @@ window.marked = marked;
       return false;
     }
     // Coalescing target for the live `thinking_tokens` counter.
-    // Holds the row currently showing the running estimate so consecutive
-    // ticks update in place instead of appending a note each. Reset
-    // implicitly: we only reuse it while it's still the last row rendered
-    // (see the nextElementSibling check), so any other event starts fresh.
+    // Holds the row + its text node so consecutive ticks update in place
+    // instead of appending a note each. Reset implicitly: we only reuse
+    // it while it's still the last row rendered (nextElementSibling ===
+    // null), so any other event starts fresh.
     let thinkingTokensRow = null;
+    let thinkingTokensText = null;
     function renderStream(v, api) {
       // Drop claude's result line and rate-limit — noise. TurnEnd
       // communicates pass/fail; rate-limit events are noisy status chatter.
@@ -1926,13 +1927,13 @@ window.marked = marked;
         // tick starts a fresh row.
         if (v.subtype === 'thinking_tokens') {
           const n = v.estimated_tokens;
-          const label = '🧠 thinking … '
+          const text = 'thinking … '
             + (n != null ? '~' + Number(n).toLocaleString() + ' tokens' : '');
           if (thinkingTokensRow && thinkingTokensRow.isConnected
               && thinkingTokensRow.nextElementSibling === null) {
-            thinkingTokensRow.textContent = label;
+            thinkingTokensText.nodeValue = text;
           } else {
-            thinkingTokensRow = api.row('note', label);
+            [thinkingTokensRow, thinkingTokensText] = api.mutableRow('note', text, '🧠');
           }
           return;
         }

frontend/packages/shared/src/terminal.css

@@ -216,11 +216,44 @@
 details.row {
   white-space: normal;
 }
+/* Two-column layout for expandable summary rows.
+   Left col: fixed-width icon cell. Right col: disclosure chevron +
+   text, wrapping within itself so no continuation line bleeds under
+   the icon. Overrides the flat-row hanging-indent metrics (.live .row
+   sets padding-left: 1.9em; text-indent: -1.4em) with explicit flex
+   geometry. The negative margin-left on summary cancels the details
+   container's inherited padding-left so the icon lands at the same
+   horizontal position as flat-row icons. */
 details.row > summary {
   cursor: pointer;
   list-style: none;
   white-space: pre-wrap;
   word-break: break-word;
+  display: flex;
+  align-items: baseline;
+  margin-left: -1.9em;
+  padding-left: 0.5em;
+  text-indent: 0;
+}
+/* Icon column: 2em accommodates wide emoji without ink bleeding into
+   the chevron column. Overrides the inline-block + width: 1.4em set
+   on .live .row-glyph for the shared flat-row context. */
+details.row > summary > .row-glyph {
+  flex: 0 0 2em;
+  width: auto;
+  text-align: center;
+}
+/* Content column: chevron (::before) + text, wraps within the cell. */
+details.row > summary > .summary-text {
+  flex: 1;
+  min-width: 0;
+}
+/* Icon-less summaries: the CSS-generated ▸/▾ acts as the hanging
+   marker. Hanging indent keeps wrapped lines under the text body,
+   not under the chevron. Mirrors the flat-row text-indent metric. */
+details.row > summary > .summary-text:only-child {
+  padding-left: 1.4em;
+  text-indent: -1.4em;
 }
 details.row > summary > .summary-text::before {
   content: '▸ ';

frontend/packages/shared/src/terminal.js

@@ -215,6 +215,22 @@ export function create(opts) {
     afterAppend(wasNearBottom);
     return e;
   }
+  // Like row(), but returns [element, textNode] so the caller can update
+  // the text in place via textNode.nodeValue. Use for rows whose content
+  // changes after initial render (e.g. live-updating counters).
+  // Text is stored as a plain text node — no linkify, no innerHTML.
+  function mutableRow(cls, text, icon) {
+    clearPlaceholder();
+    const wasNearBottom = isNearBottom();
+    const e = document.createElement('div');
+    e.className = 'row ' + (cls || '') + (currentNoAnim ? ' no-anim' : '');
+    if (icon != null && icon !== '') e.appendChild(glyphSpan(icon));
+    const tn = document.createTextNode(text == null ? '' : String(text));
+    e.appendChild(tn);
+    log.appendChild(e);
+    afterAppend(wasNearBottom);
+    return [e, tn];
+  }
   function details(cls, summary, body, icon) {
     clearPlaceholder();
     const wasNearBottom = isNearBottom();
@@ -253,7 +269,7 @@ export function create(opts) {
 
   function api(extra) {
     return Object.assign({
-      row, details, detailsDiff, placeholder, linkify,
+      row, mutableRow, details, detailsDiff, placeholder, linkify,
       fromHistory: false,
     }, extra || {});
   }
@@ -486,7 +502,7 @@ export function create(opts) {
   }
 
   const ready = start();
-  return { row, details, detailsDiff, placeholder, ready };
+  return { row, mutableRow, details, detailsDiff, placeholder, ready };
 }
 
 // Build a DocumentFragment from `text`, turning bare http(s) URLs into