Help: Fn+h lists the keys of the screen you're on, and no screen names its keys any more (#69)

Fn+h on any screen, text fields included, and ? outside Text Entry, open a
panel over the content area: the screen's own keys, then the ones that work
everywhere. Every App declares its keys for the state it is in (pages,
viewers, dialogs and text fields answer for themselves); the App manager
opens the panel and takes every key while it is open.

About 30 hint lines are gone, from every App. What stays on a screen is
state. The first-start Setup keeps its hints and teaches the key; a device
set up before gets one Toast, once. The guide and the FAQ open with it.
`key help` over the consoles.

476 host tests (8 new). Checked on the device with key help and screenshots:
the Launcher, all nine Apps and several of their states. 8.5 KB of flash and
40 bytes of static RAM. Decisions Q196 to Q203 in docs/milestones/U1.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/ui/screen.cpp

@@ -17,6 +17,7 @@ void Screen::render(AppManager& apps, const StatusInfo& status, const Toast* toa
     const auto& area = theme::kContent;
     canvas_.setClipRect(area.x, area.y, area.w, area.h);
     apps.foreground().draw(canvas_);
+    if (apps.help().isOpen()) widgets::help(canvas_, apps.help());  // over the App, under the Status Bar
     canvas_.clearClipRect();
     widgets::statusBar(canvas_, status);
     if (toast) widgets::toast(canvas_, *toast);

src/ui/widgets.cpp

@@ -175,4 +175,40 @@ void toast(Canvas& c, const Toast& t) {
     c.clearClipRect();
 }
 
+void help(Canvas& c, const HelpModel& model) {
+    const auto& area = kContent;
+    c.fillRect(area.x, area.y, area.w, area.h, kBackground);
+    c.setTextDatum(top_left);
+    c.setFont(&fonts::bold);
+    c.setTextColor(kAccent);
+    c.drawString(("Keys: " + model.title()).c_str(), 4, area.y + 1);
+    c.drawFastHLine(4, area.y + 13, area.w - 8, kMuted);
+
+    const int top = area.y + 16, keysX = 4, actionX = 70;
+    const auto& rows = model.rows();
+    int count = static_cast<int>(rows.size());
+    for (int row = 0; row < model.visibleRows(); row++) {
+        int i = model.top() + row;
+        if (i >= count) break;
+        int y = top + row * kLineHeight;
+        if (!rows[i].action) {  // a heading
+            c.setFont(&fonts::bold);
+            c.setTextColor(kMuted);
+            c.drawString(rows[i].keys, keysX, y);
+            continue;
+        }
+        c.setFont(&fonts::body);
+        c.setTextColor(kAccent);
+        c.drawString(rows[i].keys, keysX, y);
+        c.setTextColor(kText);
+        c.drawString(rows[i].action, actionX, y);
+    }
+    if (count > model.visibleRows()) {
+        int h = model.visibleRows() * kLineHeight;
+        int barH = h * model.visibleRows() / count;
+        int barY = top + (h - barH) * model.top() / (count - model.visibleRows());
+        c.fillRect(area.x + area.w - 2, barY, 2, barH, kMuted);
+    }
+}
+
 }  // namespace roro::widgets

src/ui/widgets.h

@@ -6,6 +6,7 @@
 
 #include "canvas.h"
 #include "dialog_model.h"
+#include "key_help.h"
 #include "line_editor.h"
 #include "list_model.h"
 #include "text_wrap.h"
@@ -59,6 +60,9 @@ void lineEditor(Canvas& c, const LineEditor& editor, theme::Rect area);
 
 void dialog(Canvas& c, const std::string& title, const std::string& message, const DialogModel& model);
 
+// The help panel (Fn+h): the keys of the screen under it, over the whole content area.
+void help(Canvas& c, const HelpModel& model);
+
 void toast(Canvas& c, const Toast& t);
 
 }  // namespace widgets