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.

docs/terminal-rendering.md

@@ -13,17 +13,32 @@ event kind today. Source of truth lives in
 Every row — flat `<div class="row …">` and expandable
 `<details class="row …">` alike — shares one prefix column.
 The mechanism is `padding-left + negative text-indent` on
-`.live .row`: the row's first character (the prefix glyph)
+`.live .row`: the row's first inline box gets pulled back
-gets pulled back into the column at ~0.5em, and wrapped
+into the column at ~0.5em, and wrapped continuation lines
-continuation lines hang under the body, not under the glyph.
+hang under the body, not under the glyph.
 
-`<details>` summaries inherit those metrics. The disclosure
+Rows that carry an icon (the per-tool emoji, `🧠`/`💭`
-marker (`▸` / `▾`) is supplied by CSS `summary::before` so it
+thinking, etc.) pass it as the `icon` argument to
-lands in the same column as flat-row glyphs. To make that
+`row()` / `details()` / `detailsDiff()`, which puts it in a
-work the JS-side summary text **does not** include a
+fixed-width `.row-glyph` cell (`display: inline-block;
-directional `→` / `←` — the row's colour (cyan = outbound,
+width: 1.4em`) rather than as a bare first character. The
-muted = inbound) carries the direction, and the prefix
+constant cell width means every icon's left edge lines up in
-column never has to fit two glyphs side-by-side.
+the column regardless of the glyph's rendered width (emoji
+differ; some carry a variation selector) — a flat row's `🧠`
+and a `details` summary's `🖥️` align. Rows with a plain
+single-char glyph (`◆ · ! ←`) still pass it inline; it lands
+at the same ~0.5em left edge.
+
+`<details>` summaries inherit those metrics. The icon (when
+present) sits in the `.row-glyph` cell; the summary text lives
+in a `.summary-text` span and the disclosure caret (`▸` / `▾`)
+is supplied by CSS `.summary-text::before` so it **leads the
+text, not the icon** — a leading caret on the icon would push
+it out of the shared column. Icon-less summaries have no
+`.row-glyph`, so the caret falls into the prefix column like
+the old directional glyph. The summary text carries no
+`→` / `←`; the row colour (cyan = outbound, muted = inbound)
+carries the direction.
 
 Child blocks inside a row (the `.md` markdown wrapper, an
 inner `<details>`) get `text-indent: 0` so their content

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) {
+    function detailsOpenMd(api, cls, summary, body, icon) {
-      const d = api.details(cls, summary, '');
+      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 tool icon goes in the shared `.row-glyph` cell (4th arg) so it
-        // (`→`) — the disclosure marker (`▸/▾`) from CSS sits in the
+        // lines up with flat-row icons; the summary text carries no
-        // prefix column for every row kind, and the row's cyan colour
+        // directional `→` (the row's cyan colour signals "outbound tool" and
-        // already signals "outbound tool".
+        // the CSS disclosure caret leads the text).
-        const summary = toolIcon(name) + ' ' + name + ' ' + path + ' · '
+        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` : ''),
+          'send → ' + to + (lines > 1 ? ` · ${lines}L` : ''),
-          body);
+          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` : ''),
+          'ask → ' + to + (lines > 1 ? ` · ${lines}L` : ''),
-          q);
+          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` : ''),
+          'answer #' + id + (lines > 1 ? ` · ${lines}L` : ''),
-          a);
+          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);
+        const summary = 'run* $ ' + trim(firstLine.trim(), 72);
-        return api.details('tool-use', summary, '$ ' + cmd);
+        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));
             }
           }
         }

frontend/packages/shared/src/terminal.css

@@ -84,6 +84,19 @@
   margin: 0.1em 0;
 }
 .live .row + .row { border-top: 0; }
+/* Fixed-width icon column. Rows built with an `icon` (see terminal.js
+   `row()` / `details()`) put it in a `.row-glyph` element instead of as a
+   bare first character. `inline-block` with a fixed `width` means the icon
+   occupies one constant-width cell regardless of the glyph's rendered width
+   (emoji differ; some carry a variation selector), so every icon's left edge
+   lines up — a flat-row `🧠` and a `details` summary's `🖥️` share the column.
+   It's the first inline box, so the row's `text-indent: -1.4em` pulls it into
+   the reserved prefix slot exactly like a bare glyph; the following text then
+   starts at the `padding-left` (1.9em) where wrapped lines also hang. */
+.live .row-glyph {
+  display: inline-block;
+  width: 1.4em;
+}
 /* Row-kind colours. Pages register renderers that emit these classes;
    any class no page emits is just dead CSS, which is fine. Turn-framing
    classes carry their signal entirely on the coloured border-left rule —
@@ -189,11 +202,15 @@
   opacity: 0.6;
 }
 /* Expandable rows reuse the flat-row prefix metrics (padding-left +
-   negative text-indent) so the disclosure glyph (`▸ / ▾`) lands in
+   negative text-indent). The summary's icon (when present) sits in the
-   exactly the same column as flat-row prefix glyphs (`→ ← · ◆ ✓ ✗`).
+   shared `.row-glyph` column — same cell as a flat row's icon — so a
-   Summary text omits the per-row directional glyph (the row colour
+   `details` summary's `🖥️` lines up under a flat row's `🧠`. The
-   already carries cyan = outbound tool, muted = inbound result) so
+   disclosure caret (`▸ / ▾`) leads the `.summary-text` (not the icon) via
-   the prefix column doesn't have to fit two glyphs side-by-side. */
+   `::before`, so it sits where the summary text starts rather than shoving
+   the icon out of the prefix column. Icon-less summaries have no `.row-glyph`,
+   so the caret falls back into the prefix column like the old directional
+   glyph. The summary text carries no `→ / ←`; the row colour (cyan =
+   outbound tool, muted = inbound result) carries the direction. */
 details.row {
   white-space: normal;
 }
@@ -203,11 +220,11 @@ details.row > summary {
   white-space: pre-wrap;
   word-break: break-word;
 }
-details.row > summary::before {
+details.row > summary > .summary-text::before {
   content: '▸ ';
   color: inherit;
 }
-details.row[open] > summary::before { content: '▾ '; }
+details.row[open] > summary > .summary-text::before { content: '▾ '; }
 details.row > pre.diff-body,
 details.row > pre.tool-body {
   margin: 0.3em 0 0.4em 0;

frontend/packages/shared/src/terminal.js

@@ -29,11 +29,14 @@
 //
 // Renderers receive (ev, api) where api exposes:
 //
-//   api.row(cls, text)                  → appends a flat <div class="row cls">
+//   api.row(cls, text, icon?)           → appends a flat <div class="row cls">;
-//   api.details(cls, summary, body)     → appends <details class="row cls">
+//                                          optional `icon` lands in a
-//                                          with a <pre.tool-body>
+//                                          fixed-width `.row-glyph` cell
-//   api.detailsDiff(cls, summary, body) → ditto but body is line-coloured by
+//   api.details(cls, summary, body, icon?) → appends <details class="row cls">
-//                                          leading "+ " / "- " prefix
+//                                          with a <pre.tool-body>; `icon` (if
+//                                          given) shares the `.row-glyph` column
+//   api.detailsDiff(cls, summary, body, icon?) → ditto but body is
+//                                          line-coloured by leading "+ "/"- "
 //   api.placeholder(text)               → replaces log content with a single
 //                                          muted "(placeholder)" row, cleared
 //                                          on the next real row
@@ -222,24 +225,47 @@ export function create(opts) {
     log.appendChild(e);
     placeholderEl = e;
   }
-  function row(cls, text) {
+  // A leading icon (`→ ← 🧠 🖥️ …`) goes in a fixed-width `.row-glyph`
+  // element so every row's icon lands in one column regardless of the
+  // glyph's rendered width (emoji vary; some carry variation selectors).
+  // Optional: callers that pass no `icon` keep the bare first-character
+  // prefix the older rows rely on.
+  function glyphSpan(icon) {
+    const g = document.createElement('span');
+    g.className = 'row-glyph';
+    g.textContent = icon;
+    return g;
+  }
+  // Build a <summary> whose icon (if any) sits in the shared `.row-glyph`
+  // column and whose text lives in a `.summary-text` span — the disclosure
+  // caret (CSS `.summary-text::before`) then leads the text, not the icon,
+  // so the icon stays aligned with flat-row icons.
+  function buildSummary(summary, icon) {
+    const s = document.createElement('summary');
+    if (icon != null && icon !== '') s.appendChild(glyphSpan(icon));
+    const st = document.createElement('span');
+    st.className = 'summary-text';
+    st.textContent = summary;
+    s.appendChild(st);
+    return s;
+  }
+  function row(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));
     e.appendChild(linkify(text));
     log.appendChild(e);
     afterAppend(wasNearBottom);
     return e;
   }
-  function details(cls, summary, body) {
+  function details(cls, summary, body, icon) {
     clearPlaceholder();
     const wasNearBottom = isNearBottom();
     const d = document.createElement('details');
     d.className = 'row ' + (cls || '') + (currentNoAnim ? ' no-anim' : '');
-    const s = document.createElement('summary');
+    d.appendChild(buildSummary(summary, icon));
-    s.textContent = summary;
-    d.appendChild(s);
     const pre = document.createElement('pre');
     pre.className = 'tool-body';
     pre.appendChild(linkify(body));
@@ -248,14 +274,12 @@ export function create(opts) {
     afterAppend(wasNearBottom);
     return d;
   }
-  function detailsDiff(cls, summary, body) {
+  function detailsDiff(cls, summary, body, icon) {
     clearPlaceholder();
     const wasNearBottom = isNearBottom();
     const d = document.createElement('details');
     d.className = 'row ' + (cls || '') + (currentNoAnim ? ' no-anim' : '');
-    const s = document.createElement('summary');
+    d.appendChild(buildSummary(summary, icon));
-    s.textContent = summary;
-    d.appendChild(s);
     const pre = document.createElement('pre');
     pre.className = 'tool-body diff-body';
     for (const line of String(body).split('\n')) {