Phase 1 sub-commit 4: Qt foundation types

BackendConnection (QML singleton via create() factory) reads BRIDGE_URL
and BRIDGE_TOKEN from env, periodically probes <url>/healthz with a 2s
transfer timeout, and exposes a Connecting/Online/Error state machine
plus error/token properties to QML. Bundled-mode startup (spawning the
embedded FrankenPHP child) is a Phase 4 deliverable; restart() is a
no-op for now. tokenRotated signal is reserved for the per-session
secret rotation described in PLAN.md §3.

SingleInstance is C++-only — main() must call acquireOrForward() before
the QML engine boots, so it's exposed via context property rather than
QML_SINGLETON. QLocalServer-based lock with stale-socket detection,
launch-arg forwarding via QDataStream, and the deadlock-avoiding race
fallback specified in §3 *Edge cases*.

CMakeLists.txt declares the PhpQml.Bridge static QML module with both
sources and is dual-mode: stands alone for sanity builds, integrates
via add_subdirectory from the skeleton's top-level CMake (Phase 1
sub-commit 6). Standalone build verified clean.

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

framework/qml/src/BackendConnection.cpp

@@ -0,0 +1,104 @@
+#include "BackendConnection.h"
+
+#include <QNetworkAccessManager>
+#include <QNetworkReply>
+#include <QNetworkRequest>
+#include <QQmlEngine>
+#include <QTimer>
+#include <QUrl>
+
+namespace PhpQml::Bridge {
+
+namespace {
+constexpr int kInitialProbeMs = 0;
+constexpr int kProbeIntervalMs = 5000;
+constexpr int kProbeTimeoutMs = 2000;
+} // namespace
+
+BackendConnection::BackendConnection(QObject* parent)
+    : QObject(parent)
+    , m_nam(new QNetworkAccessManager(this))
+    , m_retryTimer(new QTimer(this))
+{
+    m_url = QString::fromUtf8(qgetenv("BRIDGE_URL"));
+    m_token = QString::fromUtf8(qgetenv("BRIDGE_TOKEN"));
+
+    if (m_url.isEmpty()) {
+        // Dev-mode fallback: matches the spike's hardcoded port and
+        // documents the convention. See PLAN.md §11 *Open Questions*
+        // (system FrankenPHP collision on :8080).
+        m_url = QStringLiteral("http://127.0.0.1:8765");
+    }
+
+    m_retryTimer->setSingleShot(false);
+    m_retryTimer->setInterval(kProbeIntervalMs);
+    connect(m_retryTimer, &QTimer::timeout, this, &BackendConnection::probe);
+
+    QTimer::singleShot(kInitialProbeMs, this, &BackendConnection::probe);
+    m_retryTimer->start();
+}
+
+BackendConnection::~BackendConnection() = default;
+
+BackendConnection* BackendConnection::create(QQmlEngine* engine, QJSEngine*)
+{
+    return new BackendConnection(engine);
+}
+
+void BackendConnection::restart()
+{
+    // No-op in dev mode (Phase 1). Phase 4 re-spawns the bundled child.
+    probe();
+}
+
+void BackendConnection::probe()
+{
+    if (m_pendingReply) return;
+
+    QNetworkRequest req;
+    req.setUrl(QUrl(m_url + QStringLiteral("/healthz")));
+    req.setTransferTimeout(kProbeTimeoutMs);
+    if (!m_token.isEmpty()) {
+        req.setRawHeader("Authorization", "Bearer " + m_token.toUtf8());
+    }
+
+    m_pendingReply = m_nam->get(req);
+    connect(m_pendingReply, &QNetworkReply::finished, this, &BackendConnection::onProbeFinished);
+}
+
+void BackendConnection::onProbeFinished()
+{
+    QNetworkReply* reply = m_pendingReply;
+    m_pendingReply = nullptr;
+    if (!reply) return;
+    reply->deleteLater();
+
+    if (reply->error() == QNetworkReply::NoError) {
+        const int status = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
+        if (status == 200) {
+            setError(QString());
+            setState(ConnectionState::Online);
+            return;
+        }
+        setError(QStringLiteral("/healthz returned HTTP %1").arg(status));
+    } else {
+        setError(reply->errorString());
+    }
+    setState(ConnectionState::Error);
+}
+
+void BackendConnection::setState(ConnectionState s)
+{
+    if (m_state == s) return;
+    m_state = s;
+    emit connectionStateChanged();
+}
+
+void BackendConnection::setError(const QString& msg)
+{
+    if (m_error == msg) return;
+    m_error = msg;
+    emit errorChanged();
+}
+
+} // namespace PhpQml::Bridge

framework/qml/src/BackendConnection.h

@@ -0,0 +1,91 @@
+#pragma once
+
+#include <QObject>
+#include <QString>
+#include <QtQmlIntegration>
+
+class QNetworkAccessManager;
+class QNetworkReply;
+class QTimer;
+class QQmlEngine;
+class QJSEngine;
+
+namespace PhpQml::Bridge {
+
+/// Owns the backend lifecycle and exposes its health to QML.
+///
+/// Phase 1 implements **dev mode**: reads `BRIDGE_URL` and `BRIDGE_TOKEN`
+/// from env, periodically probes `<url>/healthz`, and reports the result
+/// as `connectionState`. Bundled mode (spawning FrankenPHP as a child)
+/// arrives in Phase 4. See PLAN.md §3 (Run modes), §7 (BackendConnection).
+class BackendConnection : public QObject
+{
+    Q_OBJECT
+    QML_ELEMENT
+    QML_SINGLETON
+
+    Q_PROPERTY(Mode mode READ mode CONSTANT)
+    Q_PROPERTY(QString url READ url CONSTANT)
+    Q_PROPERTY(QString token READ token NOTIFY tokenChanged)
+    Q_PROPERTY(ConnectionState connectionState READ connectionState NOTIFY connectionStateChanged)
+    Q_PROPERTY(QString error READ error NOTIFY errorChanged)
+
+public:
+    enum class Mode {
+        Dev,
+        Bundled,  // Phase 4
+    };
+    Q_ENUM(Mode)
+
+    /// Phase 1 surfaces only Connecting / Online / Error. The full enum
+    /// (Reconnecting, Offline) lands with the Update Semantics layer in
+    /// Phase 2 (PLAN.md §5).
+    enum class ConnectionState {
+        Connecting,
+        Online,
+        Error,
+    };
+    Q_ENUM(ConnectionState)
+
+    explicit BackendConnection(QObject* parent = nullptr);
+    ~BackendConnection() override;
+
+    static BackendConnection* create(QQmlEngine* engine, QJSEngine*);
+
+    Mode mode() const noexcept { return m_mode; }
+    QString url() const { return m_url; }
+    QString token() const { return m_token; }
+    ConnectionState connectionState() const noexcept { return m_state; }
+    QString error() const { return m_error; }
+
+    Q_INVOKABLE void restart();
+
+signals:
+    void tokenChanged();
+    void connectionStateChanged();
+    void errorChanged();
+    /// Forward-compatible signal for §3 *Edge cases — Per-session secret
+    /// rotation*. In Phase 1 dev mode it is never emitted; bundled mode
+    /// in Phase 4 will fire it on child restart.
+    void tokenRotated(const QString& newToken);
+
+private slots:
+    void probe();
+    void onProbeFinished();
+
+private:
+    void setState(ConnectionState s);
+    void setError(const QString& msg);
+
+    Mode m_mode = Mode::Dev;
+    QString m_url;
+    QString m_token;
+    ConnectionState m_state = ConnectionState::Connecting;
+    QString m_error;
+
+    QNetworkAccessManager* m_nam = nullptr;
+    QNetworkReply* m_pendingReply = nullptr;
+    QTimer* m_retryTimer = nullptr;
+};
+
+} // namespace PhpQml::Bridge

framework/qml/src/SingleInstance.cpp

@@ -0,0 +1,82 @@
+#include "SingleInstance.h"
+
+#include <QDataStream>
+#include <QLocalSocket>
+#include <QThread>
+
+namespace PhpQml::Bridge {
+
+namespace {
+constexpr int kForwardConnectTimeoutMs = 200;
+constexpr int kForwardWriteTimeoutMs = 1500;
+constexpr int kBindRetries = 3;
+constexpr int kBindRetryDelayMs = 50;
+} // namespace
+
+SingleInstance::SingleInstance(const QString& applicationId, QObject* parent)
+    : QObject(parent)
+    , m_appId(applicationId)
+{
+    connect(&m_server, &QLocalServer::newConnection, this, &SingleInstance::onNewConnection);
+}
+
+QString SingleInstance::endpointName() const
+{
+    // QLocalServer maps the name to a per-user path on Unix and a named
+    // pipe on Windows. The appId keeps multiple bridge-using apps apart.
+    return QStringLiteral("php-qml-bridge.%1").arg(m_appId);
+}
+
+bool SingleInstance::acquireOrForward(const QStringList& launchArgs)
+{
+    const QString name = endpointName();
+
+    for (int attempt = 0; attempt < kBindRetries; ++attempt) {
+        if (m_server.listen(name)) {
+            return true;  // we are the live instance
+        }
+
+        // Bind failed. Either a real instance is running (forward args), or
+        // a stale socket/pipe is left over from a crashed process (clean up
+        // and retry). Distinguish by trying to connect.
+        QLocalSocket probe;
+        probe.connectToServer(name);
+        if (probe.waitForConnected(kForwardConnectTimeoutMs)) {
+            QDataStream out(&probe);
+            out.setVersion(QDataStream::Qt_6_5);
+            out << launchArgs;
+            probe.flush();
+            probe.waitForBytesWritten(kForwardWriteTimeoutMs);
+            probe.disconnectFromServer();
+            return false;
+        }
+
+        // No live peer responding — likely stale socket. Remove and retry
+        // with a brief backoff (PLAN.md §3 *Edge cases — Single-instance
+        // launch race*).
+        QLocalServer::removeServer(name);
+        QThread::msleep(kBindRetryDelayMs);
+    }
+
+    // Exhausted retries without binding and without a live peer. Better to
+    // act as the live instance than to deadlock both processes into exiting.
+    return true;
+}
+
+void SingleInstance::onNewConnection()
+{
+    while (auto* socket = m_server.nextPendingConnection()) {
+        connect(socket, &QLocalSocket::readyRead, this, [this, socket]() {
+            QDataStream in(socket);
+            in.setVersion(QDataStream::Qt_6_5);
+            QStringList args;
+            in >> args;
+            if (in.status() == QDataStream::Ok) {
+                emit launchArgsReceived(args);
+            }
+        });
+        connect(socket, &QLocalSocket::disconnected, socket, &QLocalSocket::deleteLater);
+    }
+}
+
+} // namespace PhpQml::Bridge

framework/qml/src/SingleInstance.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <QLocalServer>
+#include <QObject>
+#include <QString>
+#include <QStringList>
+
+namespace PhpQml::Bridge {
+
+/// Per-OS-user single-instance lock with launch-arg forwarding.
+///
+/// Owned by the application's `main()`, NOT a QML singleton — the
+/// acquire-or-forward decision must run before the QML engine boots,
+/// so we cannot rely on lazy QML construction. The application exposes
+/// the live instance to QML via `setContextProperty("SingleInstance", &si)`.
+///
+/// See PLAN.md §3 (Single-instance, Edge cases — Single-instance launch race).
+class SingleInstance : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit SingleInstance(const QString& applicationId, QObject* parent = nullptr);
+
+    /// Returns true if this process is the live instance and should
+    /// continue starting up. Returns false if another instance was
+    /// already running; the launch arguments have been forwarded and
+    /// the caller must exit before creating any QML/window resources.
+    bool acquireOrForward(const QStringList& launchArgs);
+
+signals:
+    /// Emitted when a subsequent invocation forwards its launch args
+    /// to the running instance. Application code is expected to act
+    /// on this — typically focus the existing window or open a new one.
+    void launchArgsReceived(const QStringList& args);
+
+private slots:
+    void onNewConnection();
+
+private:
+    QString endpointName() const;
+
+    QString m_appId;
+    QLocalServer m_server;
+};
+
+} // namespace PhpQml::Bridge