agent terminal: inline +/- diffs on Write and Edit tool calls

Write and Edit tool_use rows used to render as the bare file path. now
they're collapsed <details> blocks with the actual change inside —
Write shows every content line prefixed '+', Edit shows old_string as
'-' lines then new_string as '+' lines. summary carries the file path
+ counts ('→  Edit /foo · -3 +5'). lines colored via diff-add /
diff-del / diff-ctx; click to expand the full body.

renderFileWriteEdit returns null for any other tool so the existing
flat-row path (fmtToolUse) is untouched.

TODO.md

@@ -42,15 +42,6 @@ Pick anything from here when relevant. Cross-cutting design notes live in
   `GET /api/state` (`status: "thinking" | "idle" | "compacting" |
   "napping"`). JS just renders. Drops the
   derive-from-events-and-pray code path.
-- **Terminal: inline diffs for Write/Edit.** Today a `Write` /
-  `Edit` tool-use row just shows the file path. Render the actual
-  change inline in the terminal: for `Edit`, a small `+`/`-`
-  per-line diff between `input.old_string` and `input.new_string`;
-  for `Write`, the first few lines of `input.content` (it's all
-  "+"). Keep collapsed by default (`<details>` like the existing
-  tool_result rollups), expand to full diff on click. Color via
-  the same `.diff-add` / `.diff-del` classes the dashboard
-  approval diff already uses.
 - **Terminal: `/model` slash command.** Operator-typeable model
   override from the terminal. Depends on the model-override work
   above; once an override mechanism exists, wire a `/model <name>`

hive-ag3nt/assets/agent.css

@@ -333,6 +333,22 @@ details.row > summary::before {
 }
 details.row[open] > summary::before { content: '▾ '; }
 details.row.tool-result-block > summary { color: var(--muted); }
+/* Inline diff body for Write / Edit tool_use rows: same shape as
+   tool-body but each line is wrapped in a span with diff-add /
+   diff-del / diff-ctx so + / - lines are colored. */
+details.row > pre.diff-body {
+  margin: 0.3em 0 0.4em 1.2em;
+  padding: 0.4em 0.6em;
+  background: rgba(255, 255, 255, 0.02);
+  border-left: 2px solid var(--purple-dim);
+  white-space: pre-wrap;
+  word-break: break-word;
+  max-height: 22em;
+  overflow-y: auto;
+}
+details.row > pre.diff-body .diff-add { color: var(--green); }
+details.row > pre.diff-body .diff-del { color: var(--red); }
+details.row > pre.diff-body .diff-ctx { color: var(--fg); }
 details.row > pre.tool-body {
   margin: 0.3em 0 0.4em 1.2em;
   padding: 0.4em 0.6em;

hive-ag3nt/assets/app.js

@@ -514,6 +514,63 @@
         default: return name + ' ' + trim(JSON.stringify(input), 200);
       }
     }
+    // Build a tool_use row for Write/Edit as a collapsed <details>
+    // showing the actual change. Returns null for any other tool so
+    // the caller falls back to the flat-row path.
+    //   Write: every input.content line is "+".
+    //   Edit:  old_string lines as "-", new_string lines as "+".
+    // Not a true diff algorithm — claude's Edit blocks are already a
+    // contiguous old/new pair, so a literal -/+ rendering is honest.
+    function renderFileWriteEdit(c) {
+      const name = c.name || '';
+      const input = c.input || {};
+      if (name !== 'Write' && name !== 'Edit') return null;
+      const path = input.file_path || '?';
+      let body;
+      let plus = 0;
+      let minus = 0;
+      if (name === 'Write') {
+        const content = String(input.content || '');
+        const lines = content.split('\n');
+        plus = lines.length;
+        body = lines.map(l => '+ ' + l).join('\n');
+      } else {
+        const oldLines = String(input.old_string || '').split('\n');
+        const newLines = String(input.new_string || '').split('\n');
+        minus = oldLines.length;
+        plus = newLines.length;
+        body = oldLines.map(l => '- ' + l).join('\n')
+             + '\n'
+             + newLines.map(l => '+ ' + l).join('\n');
+      }
+      const summary = '→  ' + name + ' ' + path + ' · '
+        + (minus ? '-' + minus + ' ' : '') + '+' + plus;
+      return detailsDiff('tool-use', summary, body);
+    }
+    function detailsDiff(cls, summary, body) {
+      clearPlaceholder();
+      const d = document.createElement('details');
+      d.className = 'row ' + (cls || '') + (currentNoAnim ? ' no-anim' : '');
+      const s = document.createElement('summary');
+      s.textContent = summary;
+      d.appendChild(s);
+      const pre = document.createElement('pre');
+      pre.className = 'tool-body diff-body';
+      // Color each line by its leading +/-.
+      for (const line of body.split('\n')) {
+        const span = document.createElement('span');
+        if (line.startsWith('+ ')) span.className = 'diff-add';
+        else if (line.startsWith('- ')) span.className = 'diff-del';
+        else span.className = 'diff-ctx';
+        span.textContent = line + '\n';
+        pre.appendChild(span);
+      }
+      d.appendChild(pre);
+      log.appendChild(d);
+      afterAppend();
+      return d;
+    }
+
     function renderToolResult(c) {
       const txt = Array.isArray(c.content)
         ? c.content.map(p => p.text || '').join('')
@@ -547,7 +604,13 @@
             const txt = (c.thinking || c.text || '').trim();
             row('thinking', txt ? '· ' + txt : '· thinking …');
           }
-          else if (c.type === 'tool_use') row('tool-use', '→  ' + fmtToolUse(c));
+          else if (c.type === 'tool_use') {
+            // Write/Edit get a collapsed +/- diff body; everything
+            // else stays as the flat row produced by fmtToolUse.
+            if (!renderFileWriteEdit(c)) {
+              row('tool-use', '→  ' + fmtToolUse(c));
+            }
+          }
         }
         return;
       }