Shell: the console's commands on the device's own screen and keyboard (#67)

An App in the Launcher that runs the same commands as USB serial and the
Debug Console, trusted like the first. It shows what the console prints
while it is open, through a second ring of the console's that exists only
meanwhile; Ctrl+b keeps only what follows your own commands. Tab completes
a command's name from the firmware's help text, Fn with up and down recalls
earlier lines, Alt with up and down scrolls back. `rm` asks first in the
Shell, `rm -f` doesn't. Nothing is kept once the App is left.

`screenshot [seconds]` saves the screen as a PNG in /screenshots on the
card, now or after a pause: written a row at a time, indexed colour with
RGB332 as the palette, in one stored deflate block.

487 host tests (11 new: the PNG writer, the Shell's log filter, Tab).
Checked on the device over the Debug Console: commands, Tab, history, a
screenshot fetched and decoded on the PC, rm with and without the question,
a delayed screenshot of another screen. 12 KB of flash; 7 KB of heap while
open. Decisions Q204 to Q212 in docs/milestones/S1.md. Safe Mode: #77.

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

lib/files/src/file_names.cpp

@@ -4,7 +4,7 @@
 
 namespace roro::files {
 
-const char* const kFirmwareFolders[] = {"/irc", "/wifi", "/updates", "/gnss", "/gemini", "/captures", "/notes"};
+const char* const kFirmwareFolders[] = {"/irc", "/wifi", "/updates", "/gnss", "/gemini", "/captures", "/notes", "/screenshots"};
 const size_t kFirmwareFolderCount = sizeof kFirmwareFolders / sizeof kFirmwareFolders[0];
 
 std::string parentOf(const std::string& path) {

lib/files/src/png_rgb332.cpp

@@ -0,0 +1,118 @@
+#include "png_rgb332.h"
+
+namespace roro::png {
+
+uint32_t crc32(uint32_t crc, const uint8_t* data, size_t len) {
+    crc = ~crc;
+    for (size_t i = 0; i < len; i++) {
+        crc ^= data[i];
+        for (int bit = 0; bit < 8; bit++) crc = (crc >> 1) ^ (0xEDB88320u & (0u - (crc & 1)));
+    }
+    return ~crc;
+}
+
+uint32_t adler32(uint32_t adler, const uint8_t* data, size_t len) {
+    uint32_t a = adler & 0xFFFF, b = adler >> 16;
+    for (size_t i = 0; i < len; i++) {
+        a = (a + data[i]) % 65521;
+        b = (b + a) % 65521;
+    }
+    return (b << 16) | a;
+}
+
+namespace {
+
+void be32(uint8_t* out, uint32_t v) {
+    out[0] = static_cast<uint8_t>(v >> 24);
+    out[1] = static_cast<uint8_t>(v >> 16);
+    out[2] = static_cast<uint8_t>(v >> 8);
+    out[3] = static_cast<uint8_t>(v);
+}
+
+size_t rawSize(int w, int h) { return static_cast<size_t>(w + 1) * h; }  // a filter byte before each row
+size_t idatSize(int w, int h) { return 2 + 5 + rawSize(w, h) + 4; }       // zlib header, block header, data, adler
+
+}  // namespace
+
+size_t Rgb332Writer::fileSize(int w, int h) {
+    return 8 + (12 + 13) + (12 + 768) + (12 + idatSize(w, h)) + 12;  // signature, IHDR, PLTE, IDAT, IEND
+}
+
+bool Rgb332Writer::put(const uint8_t* data, size_t len, bool inIdat) {
+    if (inIdat) crc_ = crc32(crc_, data, len);
+    return sink_(data, len);
+}
+
+bool Rgb332Writer::put32(uint32_t value, bool inIdat) {
+    uint8_t b[4];
+    be32(b, value);
+    return put(b, 4, inIdat);
+}
+
+bool Rgb332Writer::begin() {
+    if (w_ <= 0 || h_ <= 0 || rawSize(w_, h_) > 65535) return false;
+    static const uint8_t signature[] = {0x89, 'P', 'N', 'G', '\r', '\n', 0x1A, '\n'};
+    if (!sink_(signature, sizeof signature)) return false;
+
+    uint8_t ihdr[4 + 13] = {'I', 'H', 'D', 'R'};
+    be32(ihdr + 4, static_cast<uint32_t>(w_));
+    be32(ihdr + 8, static_cast<uint32_t>(h_));
+    ihdr[12] = 8;  // bits a pixel
+    ihdr[13] = 3;  // indexed colour
+    ihdr[14] = ihdr[15] = ihdr[16] = 0;
+    uint8_t word[4];
+    be32(word, 13);
+    if (!sink_(word, 4) || !sink_(ihdr, sizeof ihdr)) return false;
+    be32(word, crc32(0, ihdr, sizeof ihdr));
+    if (!sink_(word, 4)) return false;
+
+    // The palette: every RGB332 value is its own index, as scripts/rdbg.py expands them. Sixteen
+    // colours at a time: this runs on a task with a small stack.
+    be32(word, 768);
+    const uint8_t plteKind[] = {'P', 'L', 'T', 'E'};
+    if (!sink_(word, 4) || !sink_(plteKind, 4)) return false;
+    uint32_t plteCrc = crc32(0, plteKind, 4);
+    for (int first = 0; first < 256; first += 16) {
+        uint8_t piece[48];
+        for (int i = 0; i < 16; i++) {
+            int v = first + i;
+            piece[i * 3] = static_cast<uint8_t>((v >> 5) * 255 / 7);
+            piece[i * 3 + 1] = static_cast<uint8_t>(((v >> 2) & 7) * 255 / 7);
+            piece[i * 3 + 2] = static_cast<uint8_t>((v & 3) * 255 / 3);
+        }
+        plteCrc = crc32(plteCrc, piece, sizeof piece);
+        if (!sink_(piece, sizeof piece)) return false;
+    }
+    be32(word, plteCrc);
+    if (!sink_(word, 4)) return false;
+
+    // IDAT: a zlib stream of one stored block. Its length is known, so it can be written first.
+    size_t raw = rawSize(w_, h_);
+    be32(word, static_cast<uint32_t>(idatSize(w_, h_)));
+    if (!sink_(word, 4)) return false;
+    crc_ = 0;
+    const uint8_t head[] = {'I', 'D', 'A', 'T', 0x78, 0x01, 0x01, static_cast<uint8_t>(raw), static_cast<uint8_t>(raw >> 8),
+                            static_cast<uint8_t>(~raw), static_cast<uint8_t>(~raw >> 8)};
+    return put(head, sizeof head, true);
+}
+
+bool Rgb332Writer::row(const uint8_t* pixels) {
+    if (rows_ >= h_) return false;
+    rows_++;
+    const uint8_t filter = 0;  // none
+    adler_ = adler32(adler_, &filter, 1);
+    adler_ = adler32(adler_, pixels, static_cast<size_t>(w_));
+    return put(&filter, 1, true) && put(pixels, static_cast<size_t>(w_), true);
+}
+
+bool Rgb332Writer::end() {
+    if (rows_ != h_) return false;
+    if (!put32(adler_, true)) return false;
+    uint8_t word[4];
+    be32(word, crc_);
+    if (!sink_(word, 4)) return false;
+    static const uint8_t iend[] = {0, 0, 0, 0, 'I', 'E', 'N', 'D', 0xAE, 0x42, 0x60, 0x82};
+    return sink_(iend, sizeof iend);
+}
+
+}  // namespace roro::png

lib/files/src/png_rgb332.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+
+// A PNG of the screen, written a row at a time with almost no memory (issue #67, Q209): 8-bit
+// indexed colour with the 256 colours of RGB332 as its palette, and the pixels stored, not
+// compressed (a "stored" deflate block), so there is nothing to compress with and nothing to buffer.
+// One block holds at most 65,535 bytes: enough for the 240 x 135 screen (32,535 with its row bytes).
+namespace roro::png {
+
+uint32_t crc32(uint32_t crc, const uint8_t* data, size_t len);      // running; start from 0
+uint32_t adler32(uint32_t adler, const uint8_t* data, size_t len);  // running; start from 1
+
+class Rgb332Writer {
+   public:
+    using Sink = std::function<bool(const uint8_t* data, size_t len)>;  // false: writing failed
+
+    Rgb332Writer(int width, int height, Sink sink) : w_(width), h_(height), sink_(std::move(sink)) {}
+
+    // The file's size, known before a byte is written.
+    static size_t fileSize(int width, int height);
+
+    bool begin();                      // false: too big for one block, or the sink refused
+    bool row(const uint8_t* pixels);   // `width` bytes, RRRGGGBB each
+    bool end();
+
+   private:
+    bool put(const uint8_t* data, size_t len, bool inIdat);
+    bool put32(uint32_t value, bool inIdat);
+
+    int w_, h_, rows_ = 0;
+    Sink sink_;
+    uint32_t crc_ = 0, adler_ = 1;
+};
+
+}  // namespace roro::png