Phase 5 sub-commit 1: DevConsole + child-output capture + Ctrl+` toggle

BackendConnection now captures the bundled FrankenPHP child's merged
stdout+stderr into a 500-line ring buffer, mirrors each line through
qCInfo(lcBundled) so terminal users still see logs, and exposes
childLogTail() / childLogLine for QML.

DevConsole.qml is an opt-in monospaced viewer with auto-scroll + clear
that the skeleton and the todo example bind to Ctrl+`. Dev mode (when
BRIDGE_URL is set, no bundled child) renders an explanatory hint.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

framework/qml/src/BackendConnection.cpp

@@ -261,7 +261,11 @@ bool BackendConnection::spawnChild(QString* errorOut)
     env.insert(QStringLiteral("MERCURE_PUBLISHER_JWT_KEY"),  m_jwtSecret);
     env.insert(QStringLiteral("MERCURE_SUBSCRIBER_JWT_KEY"), m_jwtSecret);
     m_child->setProcessEnvironment(env);
-    m_child->setProcessChannelMode(QProcess::ForwardedChannels);
+    // Capture both streams into a single chronological buffer so the
+    // DevConsole sees stderr (FrankenPHP / Symfony logs) interleaved with
+    // stdout the same way a TTY would. The console keeps still emitting
+    // each line via qCInfo(lcBundled) so terminal users aren't blinded.
+    m_child->setProcessChannelMode(QProcess::MergedChannels);
 
     // Linux: kernel kills the child if the parent dies for any reason.
     m_child->setChildProcessModifier([] {
@@ -270,6 +274,8 @@ bool BackendConnection::spawnChild(QString* errorOut)
 
     connect(m_child, &QProcess::finished,
             this, &BackendConnection::onChildFinished);
+    connect(m_child, &QProcess::readyReadStandardOutput,
+            this, &BackendConnection::onChildOutputReady);
 
     qCInfo(lcBundled) << "spawning frankenphp on port" << m_port;
     m_child->start();
@@ -296,6 +302,38 @@ void BackendConnection::teardownChild()
     disconnect(m_child, nullptr, this, nullptr);
     m_child->deleteLater();
     m_child = nullptr;
+    m_childLogBuffer.clear();
+}
+
+void BackendConnection::onChildOutputReady()
+{
+    if (!m_child) return;
+    m_childLogBuffer += QString::fromUtf8(m_child->readAllStandardOutput());
+
+    int nl;
+    while ((nl = m_childLogBuffer.indexOf(QLatin1Char('\n'))) >= 0) {
+        QString line = m_childLogBuffer.left(nl);
+        m_childLogBuffer.remove(0, nl + 1);
+        if (line.endsWith(QLatin1Char('\r'))) {
+            line.chop(1);
+        }
+        qCInfo(lcBundled).noquote() << line;
+        m_childLog.enqueue(line);
+        while (m_childLog.size() > kChildLogMax) {
+            m_childLog.dequeue();
+        }
+        emit childLogLine(line);
+    }
+}
+
+QStringList BackendConnection::childLogTail() const
+{
+    QStringList out;
+    out.reserve(m_childLog.size());
+    for (const QString& l : m_childLog) {
+        out.append(l);
+    }
+    return out;
 }
 
 void BackendConnection::onChildFinished(int exitCode, QProcess::ExitStatus status)

framework/qml/src/BackendConnection.h

@@ -3,7 +3,9 @@
 #include <QElapsedTimer>
 #include <QObject>
 #include <QProcess>
+#include <QQueue>
 #include <QString>
+#include <QStringList>
 #include <QtQmlIntegration>
 
 class QNetworkAccessManager;
@@ -78,6 +80,11 @@ public:
     /// after this completes; emits `updateApplied` / `updateApplyFailed`.
     Q_INVOKABLE void applyUpdate();
 
+    /// Returns a snapshot of the captured child stdout/stderr ring buffer
+    /// (most recent kChildLogMax lines). Bundled mode only — empty in dev
+    /// mode. Used by `DevConsole.qml` to seed its view on first show.
+    Q_INVOKABLE QStringList childLogTail() const;
+
 signals:
     void urlChanged();
     void tokenChanged();
@@ -94,10 +101,16 @@ signals:
     void updateApplied();
     void updateApplyFailed(const QString& reason);
 
+    /// Emitted for each newline-terminated chunk read from the bundled
+    /// FrankenPHP child's merged stdout+stderr stream. DevConsole.qml
+    /// listens for these to populate its log view live.
+    void childLogLine(const QString& line);
+
 private slots:
     void probe();
     void onProbeFinished();
     void onChildFinished(int exitCode, QProcess::ExitStatus status);
+    void onChildOutputReady();
     void onUpdateCheckFinished(int exitCode, QProcess::ExitStatus status);
     void onUpdateApplyFinished(int exitCode, QProcess::ExitStatus status);
 
@@ -138,6 +151,10 @@ private:
     int m_supervisorRetries = 0;
     static constexpr int kMaxSupervisorRetries = 5;
 
+    QQueue<QString> m_childLog;
+    QString m_childLogBuffer;
+    static constexpr int kChildLogMax = 500;
+
     QProcess* m_updateCheck = nullptr;
     QProcess* m_updateApply = nullptr;