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/apps/file_viewer.cpp

@@ -265,6 +265,30 @@ void FileViewer::openPacket(int index) {
     mode_ = Mode::Packet;
 }
 
+void FileViewer::help(std::vector<KeyHelp>& out) const {
+    if (confirm_) return help::dialog(out);
+    switch (mode_) {
+        case Mode::Packet:
+            out.push_back({"; .", "scroll"});
+            out.push_back({"Enter", "back to the packets"});
+            return;
+        case Mode::Text:
+        case Mode::Hex:
+            out.push_back({"; .", "a line up, down"});
+            out.push_back({", /", "a page up, down"});
+            out.push_back({"t  b", "the top, the end"});
+            if (mode_ == Mode::Text) out.push_back({"e", "edit it (up to 16 KB)"});
+            break;
+        case Mode::Pcap:
+            help::list(out, "the packet");
+            out.push_back({", /", "a page up, down"});
+            break;
+        case Mode::Ota: out.push_back({"Enter", "install it, if it's genuine"}); break;
+        case Mode::Gpx: break;
+    }
+    out.push_back({"Tab", mode_ != base_ ? "back to the file's own view" : base_ == Mode::Hex || base_ == Mode::Gpx ? "the file as text" : "the file as hex"});
+}
+
 bool FileViewer::onKey(const KeyEvent& e) {
     if (confirm_) {
         confirm_->onKey(e);
@@ -380,7 +404,7 @@ void FileViewer::draw(Canvas& c) {
     refresh();
     c.setTextDatum(top_left);
     theme::Rect body{area.x, area.y + 10, area.w, kRows * theme::kLineHeight};
-    std::string right, keys = "Tab: hex";
+    std::string right;
     bool scanning = scan_ && !scan_->done;
 
     switch (mode_) {
@@ -396,8 +420,6 @@ void FileViewer::draw(Canvas& c) {
                 c.fillRect(area.w - 2, barY, 2, barH, theme::kMuted);
             }
             right = formatBytes(size_);
-            keys = std::string("Tab: ") + (mode_ != base_ ? "back" : mode_ == Mode::Text ? "hex" : "text") + "  t: top  b: end";
-            if (mode_ == Mode::Text) keys += "  e: edit";
             break;
         }
         case Mode::Gpx: {
@@ -407,7 +429,6 @@ void FileViewer::draw(Canvas& c) {
             else if (scan_) lines = scan_->gpx.lines();
             widgets::textLines(c, lines, 0, body);
             right = formatBytes(size_);
-            keys = "Tab: the file as text";
             break;
         }
         case Mode::Pcap: {
@@ -423,7 +444,6 @@ void FileViewer::draw(Canvas& c) {
                     return row < shown_.size() ? shown_[row] : std::string();
                 });
                 right = std::to_string(scan_->packets.size()) + (scan_->morePackets ? "+ packets" : " packets");
-                keys = "Enter: the packet  Tab: hex";
             }
             break;
         }
@@ -447,7 +467,6 @@ void FileViewer::draw(Canvas& c) {
             }
             widgets::textLines(c, lines, 0, body);
             right = formatBytes(size_);
-            keys = ok ? "Enter: install  Tab: hex" : "Tab: hex";
             if (confirm_) {
                 widgets::dialog(c, "Install update?", "The device restarts into " + scan_->version + " once it's written.", *confirm_);
                 return;
@@ -464,7 +483,7 @@ void FileViewer::draw(Canvas& c) {
     c.drawString(right.c_str(), area.w - 3, area.y + 1);
     c.setTextDatum(top_left);
     if (!message_.empty()) c.setTextColor(theme::kWarning);
-    c.drawString(message_.empty() ? keys.c_str() : message_.c_str(), 4, area.y + area.h - 9);
+    if (!message_.empty()) c.drawString(message_.c_str(), 4, area.y + area.h - 9);
 }
 
 }  // namespace roro