agent-ui: real fixed-width icon column for terminal rows

Replaces the first-character-glyph + negative-text-indent trick (which let a
wide emoji or a leading disclosure caret knock the icon out of column) with a
genuine icon cell.

terminal.js: row() / details() / detailsDiff() take an optional `icon` that
goes in a fixed-width `.row-glyph` element (inline-block, 1.4em). Details
summaries wrap their text in a `.summary-text` span; the disclosure caret
moves to `.summary-text::before` so it leads the text, not the icon — keeping
the icon in the shared column. terminal.css carries the cell + caret rules.

app.js passes the per-tool emoji as `icon` for the flat tool-use row and every
expandable tool summary (Write/Edit/send/ask/answer/bash) plus the 💭 thinking
row, instead of string-prefixing it. A details `🖥️` now lines up under a flat
row's `🧠` regardless of emoji width. Doc: terminal-rendering.md layout
contract updated. Closes #1844.

frontend/packages/agent/src/app.js

@@ -1439,8 +1439,8 @@ window.marked = marked;
     // Used by send / ask / answer tool_use renderers and by `recv`
     // tool_result so message-bearing rows show their content inline
     // without an extra click.
-    function detailsOpenMd(api, cls, summary, body) {
-      const d = api.details(cls, summary, '');
+    function detailsOpenMd(api, cls, summary, body, icon) {
+      const d = api.details(cls, summary, '', icon);
       d.open = true;
       const pre = d.querySelector('pre.tool-body');
       if (pre) {
@@ -1592,13 +1592,13 @@ window.marked = marked;
                + '\n'
                + newLines.map(l => '+ ' + l).join('\n');
         }
-        // Summaries on expandable rows omit the row's directional glyph
-        // (`→`) — the disclosure marker (`▸/▾`) from CSS sits in the
-        // prefix column for every row kind, and the row's cyan colour
-        // already signals "outbound tool".
-        const summary = toolIcon(name) + ' ' + name + ' ' + path + ' · '
+        // The tool icon goes in the shared `.row-glyph` cell (4th arg) so it
+        // lines up with flat-row icons; the summary text carries no
+        // directional `→` (the row's cyan colour signals "outbound tool" and
+        // the CSS disclosure caret leads the text).
+        const summary = name + ' ' + path + ' · '
           + (minus ? '-' + minus + ' ' : '') + '+' + plus;
-        return api.detailsDiff('tool-use', summary, body);
+        return api.detailsDiff('tool-use', summary, body, toolIcon(name));
       }
       // Message-bearing tools render default-open with a markdown body so
       // the operator sees the content without an extra click. send / ask
@@ -1608,16 +1608,16 @@ window.marked = marked;
         const body = String(input.body || '');
         const lines = body.split('\n').length;
         return detailsOpenMd(api, 'tool-use',
-          toolIcon(name) + ' send → ' + to + (lines > 1 ? ` · ${lines}L` : ''),
-          body);
+          'send → ' + to + (lines > 1 ? ` · ${lines}L` : ''),
+          body, toolIcon(name));
       }
       if (name === 'mcp__hyperhive__ask') {
         const to = input.to || 'operator';
         const q = String(input.question || '');
         const lines = q.split('\n').length;
         const d = detailsOpenMd(api, 'tool-use',
-          toolIcon(name) + ' ask → ' + to + (lines > 1 ? ` · ${lines}L` : ''),
-          q);
+          'ask → ' + to + (lines > 1 ? ` · ${lines}L` : ''),
+          q, toolIcon(name));
         // When the ask targets the operator, mount an inline answer
         // slot in the live terminal — see docs/web-ui.md::Per-agent
         // page (Ask → operator inline-answer binding) for the slot
@@ -1646,8 +1646,8 @@ window.marked = marked;
         const a = String(input.answer || '');
         const lines = a.split('\n').length;
         return detailsOpenMd(api, 'tool-use',
-          toolIcon(name) + ' answer #' + id + (lines > 1 ? ` · ${lines}L` : ''),
-          a);
+          'answer #' + id + (lines > 1 ? ` · ${lines}L` : ''),
+          a, toolIcon(name));
       }
       // Bash task runner — show full command in an expandable pre block so
       // multi-line scripts are readable. Summary uses the first line so the
@@ -1655,8 +1655,8 @@ window.marked = marked;
       if (name === 'mcp__bash__run') {
         const cmd = String(input.cmd || '');
         const firstLine = cmd.split('\n')[0];
-        const summary = toolIcon(name) + ' run* $ ' + trim(firstLine.trim(), 72);
-        return api.details('tool-use', summary, '$ ' + cmd);
+        const summary = 'run* $ ' + trim(firstLine.trim(), 72);
+        return api.details('tool-use', summary, '$ ' + cmd, toolIcon(name));
       }
       return null;
     }
@@ -1803,12 +1803,12 @@ window.marked = marked;
           }
           else if (c.type === 'thinking') {
             const txt = (c.thinking || c.text || '').trim();
-            api.row('thinking', txt ? '💭 ' + txt : '💭 thinking …');
+            api.row('thinking', txt || 'thinking …', '💭');
           }
           else if (c.type === 'tool_use') {
             if (c.id && c.name) toolNameById.set(c.id, c.name);
             if (!renderRichToolUse(c, api)) {
-              api.row('tool-use', toolIcon(c.name) + ' ' + fmtToolUse(c));
+              api.row('tool-use', fmtToolUse(c), toolIcon(c.name));
             }
           }
         }