v0.8.10: settings dialog (provider, model, key), window starts on a provider

The window could be started, but it could not be pointed anywhere: a provider,
a model and a key only came in on the command line. The gear in the header now
opens a dialog that changes all three on the engine's live config.

AgentCore (app/src/core/AgentCore.*):
- providers(): the engine's preset table (cst_provider_count/at), with base
  URL, the remembered or preset model, whether a key exists and where it comes
  from (cst_creds_resolve: "saved", or the environment variable), the preset's
  key variable and the source ("built-in" / "user"). A key is read into a local
  buffer only to answer "is there one"; it never leaves the C++ side.
- modelChoices(provider): the provider's own list (cst_provider_models), the
  fetched cache (cst_ps_cached -- which writes through its out-parameters, so
  it takes a real int, not NULL: passing one cost a segfault) and the
  remembered pick. No network. modelInfo() is cst_model_info + its "200K ·
  text only" label; usage() is cst_agent_usage for the session and the turn.
- useProvider(provider, model, key) -> "" or a reason: a different provider
  goes through cst_ps_switch_provider() (the key is verified against /models
  before it is saved; offline it is kept unverified and the header says so),
  a key for the current one through cst_ps_set_key(), and the model is
  remembered in settings.json. syncConfig() takes the engine's config back
  over the app's copy, so provider/model/approval read correctly afterwards.
  The engine's session is never touched by a switch.
- open() no longer starts with an empty provider: it takes the one the engine
  used last (settings.json), else the built-in default, plus that provider's
  base URL and model. Without this the first turn could not be sent at all and
  no entry in the dialog was "in use".

QML (app/qml/SettingsDialog.qml, Main.qml):
- a modal dialog with the themed surface the other dialogs use (the Basic
  style's light panel washes out the dark theme), the provider list with its
  key state, a model field with the info label and clickable candidates, a
  password field for a new key, the session's token counters, and a note that
  reports what the last "Use this" answered.

Tests: 8 more checks -- the presets are readable, an unknown provider is
refused, the counters are readable, the gear opens the panel, the rows exist, a
model typed into the field reaches the engine, the note says so, Close puts the
dialog away. 36 checks pass. --uitest also points XDG_CONFIG_HOME at its
scratch directory now, so a run cannot rewrite the user's settings.json or
credentials, and CST_APP_SHOT writes shot.png at the end plus
shot-settings.png while the dialog is open (that is how the dialog above was
reviewed on a machine without a screen).

Verified: 36/36 UI checks, --selftest, ctest cst-app-selftest, make check rc=0,
and a screenshot of the dialog.

Version 0.8.10.

app/src/ui/UiTest.cpp

@@ -135,6 +135,24 @@ QString writeFixtureSession(const QString &ws, const QString &id) {
   return id;
 }
 
+/* A picture of an interesting state on request: the only way to look at the
+ * layout on a machine without a screen (CST_APP_SHOT=shot.png makes the run
+ * write shot.png at the end and shot-settings.png while the settings dialog
+ * is open). */
+void maybeShot(QQuickWindow *win, const QString &suffix) {
+  if (!qEnvironmentVariableIsSet("CST_APP_SHOT"))
+    return;
+  const QString base = qEnvironmentVariable("CST_APP_SHOT");
+  const QString path =
+      suffix.isEmpty() ? base
+      : base.endsWith(QLatin1String(".png"))
+          ? base.left(base.size() - 4) + suffix + QStringLiteral(".png")
+          : base + suffix + QStringLiteral(".png");
+  std::printf("%s %s\n",
+              win->grabWindow().save(path) ? "note wrote" : "note cannot write",
+              qPrintable(path));
+}
+
 }  // namespace
 
 int runUiTest(AgentCore &core, const QString &size) {
@@ -278,6 +296,40 @@ int runUiTest(AgentCore &core, const QString &size) {
   check(core.sessionId() == fixture && list && list->property("count").toInt() == 5,
         QStringLiteral("switching back replays it again"));
 
+  /* --- provider, model, key: the settings dialog ------------------------ */
+  check(core.providers().size() > 0 &&
+            !core.providers().first().toMap().value(QStringLiteral("name"))
+                 .toString()
+                 .isEmpty(),
+        QStringLiteral("the provider presets are readable"));
+  check(core.useProvider(QStringLiteral("no-such-provider"), QString(), QString())
+            .contains(QLatin1String("no such provider")),
+        QStringLiteral("switching to an unknown provider is refused"));
+  check(core.usage().contains(QStringLiteral("requests")),
+        QStringLiteral("the token counters are readable"));
+
+  clickMouse(win, QStringLiteral("settingsButton"));
+  QQuickItem *panel = item(win, QStringLiteral("settingsPanel"));
+  check(panel && panel->isVisible(), QStringLiteral("the gear opens the settings dialog"));
+  check(countNamed(win->contentItem(), QStringLiteral("providerRow:")) > 0,
+        QStringLiteral("the dialog lists the providers"));
+  maybeShot(win, QStringLiteral("-settings"));
+  QQuickItem *mfield = item(win, QStringLiteral("settingsModel"));
+  if (mfield && panel) {
+    mfield->setProperty("text", QStringLiteral("cst-test-model"));
+    clickMouse(win, QStringLiteral("settingsApply"));
+    check(core.model() == QLatin1String("cst-test-model"),
+          QStringLiteral("the model picked in the dialog reaches the engine"));
+    QQuickItem *note = item(win, QStringLiteral("settingsNote"));
+    check(note && note->property("text").toString().contains(
+                      QLatin1String("cst-test-model")),
+          QStringLiteral("the dialog says what it is using now"));
+    clickMouse(win, QStringLiteral("settingsClose"));
+    check(!panel->isVisible(), QStringLiteral("Close puts the dialog away"));
+  } else {
+    check(false, QStringLiteral("the dialog has a model field"));
+  }
+
   /* --- a narrow window: dock -> drawer, and the button opens it --- */
   resizeTo(win, 460, 900);
   check(docked && !docked->isVisible(),
@@ -295,15 +347,8 @@ int runUiTest(AgentCore &core, const QString &size) {
   check(docked && docked->isVisible(),
         QStringLiteral("widening again docks the sidebar back"));
 
-  /* A picture of the last state on request: the only way to look at the
-   * layout on a machine without a screen
-   * (CST_APP_SHOT=shot.png cst-agent-app --uitest). */
-  if (qEnvironmentVariableIsSet("CST_APP_SHOT")) {
-    const QString shot = qEnvironmentVariable("CST_APP_SHOT");
-    std::printf("%s %s\n",
-                win->grabWindow().save(shot) ? "note wrote" : "note cannot write",
-                qPrintable(shot));
-  }
+  /* A picture of the last state on request (see maybeShot). */
+  maybeShot(win, QString());
 
   std::printf("--- %s\n", g_fail ? "FAILED" : "all UI checks passed");
   return g_fail ? 1 : 0;