G1 step 4: the Gemini App (rendering, links, history, address line)

Gemtext as Q75 has it: headings bold (# in the accent colour), lists
with a middle dot, quotes muted, links as » labels, preformatted lines
unwrapped and scrolled sideways together; other text/* as is. Pages are
wrapped once for each line's first row (4 bytes a line) and only the
lines on screen are wrapped again to draw. Tab and Shift+Tab move
between links, Enter follows (relative links resolved), Back or Delete
go back to where the page was scrolled, g opens the address line.
Non-Gemini links say so in the URL bar; a changed certificate opens a
dialog; errors and refusals get a page with a "Try again" link; a page
only partly in memory says why at its end.

A status message timed with millis() after the loop's clock read was
cleared before it was drawn (unsigned wrap): now a signed comparison,
as for the toasts in M0.

Verified on the device: start page, Project Gemini, its relative news/
link, Back with the scroll restored, and the YouTube link refused.

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

src/apps/gemini_app.h

@@ -0,0 +1,64 @@
+#pragma once
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "app.h"
+#include "dialog_model.h"
+#include "gemtext.h"
+#include "line_editor.h"
+#include "services/gemini_service.h"
+#include "ui/canvas.h"
+
+namespace roro {
+
+// Geminispace on the Cardputer (docs/milestones/G1.md). Pages come from the GeminiService as
+// lines; the App wraps them once (keeping only each line's first row), then wraps just the lines
+// on screen when it draws, so a long page costs 4 bytes a line on top of its text.
+class GeminiApp : public App {
+   public:
+    explicit GeminiApp(GeminiService& gemini) : gemini_(gemini) {}
+    void onEnter() override;
+    bool onKey(const KeyEvent& e) override;
+    bool textEntryActive() const override { return addressOpen_; }
+    void update(uint32_t nowMs) override;
+    void draw(Canvas& c) override;
+
+   private:
+    struct Visit {
+        std::string url;
+        int topRow;
+    };
+
+    void navigate(const std::string& url, bool remember = true);
+    void show(GeminiPage&& page);
+    void showMessage(const std::string& url, const std::string& gemtext);
+    void layout(Canvas& c);
+    void drawLine(Canvas& c, size_t index, int firstRow, int y, int rows);
+    std::vector<std::string> rowsOf(Canvas& c, size_t index) const;
+    gemini::GemLine lineAt(size_t index) const;
+    int rowsOnScreen() const;
+    void selectLink(int direction);
+    void scrollTo(int row);
+
+    GeminiService& gemini_;
+    GeminiPage page_;
+    std::vector<uint8_t> types_;      // per source line: gemini::LineType
+    std::vector<uint32_t> firstRow_;  // per source line, plus the total at the end
+    std::vector<uint32_t> links_;     // source lines that are links
+    bool layoutDirty_ = true;
+    int topRow_ = 0, hscroll_ = 0;
+    int selected_ = -1;  // into links_
+    int restoreRow_ = -1;  // going back: where that page was scrolled to, applied after layout
+    std::vector<Visit> history_;
+    bool loading_ = false;
+    std::string loadingUrl_, status_;
+    uint32_t statusMs_ = 0;
+    bool addressOpen_ = false;
+    LineEditor address_{1024};
+    std::unique_ptr<DialogModel> certDialog_;
+    GeminiPage pendingCert_;
+};
+
+}  // namespace roro