Initial commit: Chatter — assistive-writing app for reMarkable Paper Pro Move

Direct-framebuffer ink pipeline (stock-quality strokes), finger-wipe erase,
growable scrolling canvas with color-ghost cleanup, bidirectional toggle with a
persistent 4-finger return launcher, instant button feedback. Includes prebuilt
aarch64 binaries (dist/), build/deploy/install scripts, a user guide, and a
complete technical reference.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/fbdump.cpp

@@ -0,0 +1,56 @@
+// Framebuffer snapshot shim: preloaded into xochitl, it captures the e-paper
+// framebuffer (via setBuffers) and, when the trigger file /tmp/fbdump appears,
+// saves the current framebuffer to /home/root/fbdump.png. Used to recover the
+// real Calligraphy nib angle by measuring xochitl's actual rendered strokes.
+
+#define _GNU_SOURCE 1
+#include <QImage>
+#include <tuple>
+#include <dlfcn.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <cstdio>
+
+namespace {
+uchar *g_bits = nullptr;
+int g_w = 0, g_h = 0, g_bpl = 0, g_fmt = 0;
+bool g_started = false;
+
+void *dumper(void *)
+{
+    fprintf(stderr, "FBSHIM dumper thread started\n");
+    for (;;) {
+        usleep(400000);
+        struct stat st;
+        if (g_bits && stat("/tmp/fbdump", &st) == 0) {
+            QImage snap = QImage(g_bits, g_w, g_h, g_bpl, QImage::Format(g_fmt)).copy();
+            bool ok = snap.save("/home/root/fbdump.png");
+            if (!ok) ok = snap.save("/home/root/fbdump.bmp", "BMP");
+            ::unlink("/tmp/fbdump");
+            fprintf(stderr, "FBDUMP %dx%d saved ok=%d\n", g_w, g_h, int(ok));
+        }
+    }
+    return nullptr;
+}
+}
+
+extern "C" void _ZN13EPFramebuffer10setBuffersESt5tupleIJ6QImageS1_EEPS1_(
+    void *self, void *tuplePtr, void *imgPtr)
+{
+    static void (*real)(void *, void *, void *) = nullptr;
+    if (!real)
+        real = (void (*)(void *, void *, void *))dlsym(
+            RTLD_NEXT, "_ZN13EPFramebuffer10setBuffersESt5tupleIJ6QImageS1_EEPS1_");
+    auto *t = reinterpret_cast<std::tuple<QImage, QImage> *>(tuplePtr);
+    const QImage &a = std::get<0>(*t);
+    g_bits = const_cast<uchar *>(a.constBits());
+    g_w = a.width(); g_h = a.height(); g_bpl = a.bytesPerLine(); g_fmt = int(a.format());
+    fprintf(stderr, "FBSHIM setBuffers %dx%d fmt=%d\n", g_w, g_h, g_fmt);
+    if (!g_started) {
+        g_started = true;
+        pthread_t th;
+        pthread_create(&th, nullptr, dumper, nullptr);
+    }
+    if (real) real(self, tuplePtr, imgPtr);
+}