fix(acp): stop italic thinking text from clipping

Layout the thought body inside the padded viewport so the last glyphs
do not open a horizontal scrollbar.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: nullmastermind

src/widgets/AcpMessageWidget.cpp

@@ -83,6 +83,12 @@ constexpr const char *kFrameStyleAssistant =
     "AcpMessageWidget[role=\"assistant\"][goalSet=\"true\"] { background: rgba(180, 140, 50, 48); border: 1px solid rgba(180, 140, 50, 80); border-radius: 6px; }";
 constexpr const char *kFrameStyleThought =
     "AcpMessageWidget[role=\"thought\"] { background: palette(base); border-radius: 6px; }";
+// Extra left inset under "Thinking…". Not in the layout margins — those wrap
+// the header too. Italic glyphs also overhang their advance by a few px, so
+// wrap width must leave that slack inside the viewport or the last letters
+// clip and QTextBrowser opens a horizontal scroll range.
+constexpr int kThoughtBrowserPadLeft = 4;
+constexpr int kThoughtItalicRightSlack = 4;
 constexpr const char *kFrameStyleSystem =
     "AcpMessageWidget[role=\"system\"] { background: rgba(180, 140, 50, 32); border: 1px solid rgba(180, 140, 50, 60); border-radius: 6px; }";
 
@@ -219,7 +225,10 @@ AcpMessageWidget::AcpMessageWidget(QString role, QWidget *parent)
         m_layout->addWidget(m_thoughtHeader);
 
         m_browser = new QTextBrowser(this);
-        m_browser->setStyleSheet(QStringLiteral("QTextBrowser { background: transparent; border: none; font-style: italic; padding-left: 4px; }"));
+        m_browser->setStyleSheet(
+            QStringLiteral("QTextBrowser { background: transparent; border: none; "
+                           "font-style: italic; padding-left: %1px; }")
+                .arg(kThoughtBrowserPadLeft));
         m_browser->setOpenExternalLinks(true);
         configureBubbleBrowser(m_browser);
         // QTextDocument paragraphs carry an implicit ~12px bottom margin even
@@ -535,12 +544,16 @@ void AcpMessageWidget::refitBrowserHeight()
         // already have unless we just collapsed to header-only above.
         return;
     }
+    int textW = w;
+    if (m_thoughtHeader) {
+        textW = qMax(0, w - kThoughtBrowserPadLeft - kThoughtItalicRightSlack);
+    }
     QTextDocument *doc = m_browser->document();
     // Force a full layout pass for the current width before measuring —
     // QTextDocument under-reports height for freshly-set multi-line text
     // until the layout engine has run, which clips an expanded thought down
     // to roughly its first line.
-    const int browserH = qMax(0, static_cast<int>(std::ceil(layoutDocumentHeight(doc, w))));
+    const int browserH = qMax(0, static_cast<int>(std::ceil(layoutDocumentHeight(doc, textW))));
     m_browser->setFixedHeight(browserH);
     bubbleH += browserH;
     setFixedHeight(bubbleH);

tests/test_acp_message_widget_streaming.cpp

@@ -22,6 +22,7 @@ private slots:
     void thought_collapse_after_streaming_done();
     void thought_renders_markdown_as_raw_text();
     void thought_keeps_body_height_while_hidden();
+    void thought_body_does_not_overflow_viewport();
     void thought_reexpand_while_hidden_restores_body_height();
 };
 
@@ -127,6 +128,33 @@ void TestAcpMessageWidgetStreaming::thought_keeps_body_height_while_hidden()
                             .arg(collapsedH)));
 }
 
+void TestAcpMessageWidgetStreaming::thought_body_does_not_overflow_viewport()
+{
+    // Thought body has stylesheet padding-left and italic glyphs that overhang
+    // their advance. Layout at the frame content width makes the document a
+    // few px wider than the viewport: horizontal scroll + clipped last letters.
+    AcpMessageWidget w(QStringLiteral("thought"));
+    w.resize(420, 40);
+    w.setText(QStringLiteral(
+        "The compile timed out again at 300s while compiling. The crate is huge. "
+        "I need a longer timeout. 0 disable. the deadline? The bash tool says "
+        "timeout 0 disables the command deadline. I should set timeout 0."));
+
+    auto *browser = w.findChild<QTextBrowser *>();
+    QVERIFY(browser);
+    QTextDocument *doc = browser->document();
+    QVERIFY(doc);
+
+    const qreal contentW = w.width() - 8; // thought layout margins 4+4
+    QVERIFY(doc->textWidth() > 0);
+    // Must leave pad-left (4) plus italic overhang slack (>=2) inside the
+    // allocated width. Equality with contentW is the bug this test exists for.
+    QVERIFY2(doc->textWidth() <= contentW - 4 - 2,
+             qPrintable(QStringLiteral("textWidth=%1 contentW=%2")
+                            .arg(doc->textWidth())
+                            .arg(contentW)));
+}
+
 void TestAcpMessageWidgetStreaming::thought_reexpand_while_hidden_restores_body_height()
 {
     AcpMessageWidget w(QStringLiteral("thought"));