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>

scripts/build.sh

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+#!/usr/bin/env bash
+# Cross-build Chatter with the reMarkable Paper Pro Move (Chiappa) SDK.
+#
+# Usage: scripts/build.sh [extra cmake args]
+# Override SDK location with CHATTER_SDK=...
+set -euo pipefail
+
+SDK="${CHATTER_SDK:-/home/ack/external/remarkable-sdk/chiappa-3.27.0.97}"
+ENV="$SDK/environment-setup-cortexa55-remarkable-linux"
+[ -f "$ENV" ] || { echo "SDK env-setup not found: $ENV"; exit 1; }
+
+cd "$(dirname "$0")/.."
+
+# Yocto SDKs refuse to operate with LD_LIBRARY_PATH set (Jatke sets it globally).
+unset LD_LIBRARY_PATH
+# shellcheck disable=SC1090
+. "$ENV"
+
+cmake -S . -B build "$@"
+cmake --build build -j"$(nproc)"
+echo "built: build/chatter"
+
+# The return-to-Chatter launcher is a tiny standalone C daemon (not part of the
+# CMake target). Build it here too so install-launcher.sh has its binary.
+# $CC carries flags (mcpu, sysroot, …) so it must stay UNquoted.
+# shellcheck disable=SC2086
+$CC -O2 -o tools/chatter-launcher tools/chatter_launcher.c
+echo "built: tools/chatter-launcher"

scripts/chatter-launcher.service

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+[Unit]
+Description=Chatter launcher (multi-finger gesture watcher)
+After=home.mount data.mount multi-user.target
+# Binary + scripts live on the persistent /home volume.
+RequiresMountsFor=/home/root/chatter
+
+[Service]
+ExecStart=/home/root/chatter/chatter-launcher
+Restart=always
+RestartSec=2
+
+[Install]
+WantedBy=multi-user.target

scripts/deploy-and-run.sh

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+#!/usr/bin/env bash
+# Deploy the chatter binary to the tablet and run it on the e-paper display.
+#
+# Usage: scripts/deploy-and-run.sh [path-to-binary]
+#   default binary: build/chatter
+#
+# Requires: `ssh chatter` working (see doc/tablet_access.md).
+#
+# IMPORTANT lessons baked in here:
+#  * The e-paper framebuffer is a singleton guarded by an flock
+#    (/tmp/epframebuffer.lock). Only ONE process may hold it. A stranded
+#    instance blanks the panel for everyone, so we always stop the previous
+#    chatter unit first.
+#  * Launch as a transient systemd service (systemd-run), NOT an ssh background
+#    job: that detaches cleanly (no held SSH channel) and is stoppable via
+#    `systemctl stop chatter`.
+#  * xochitl owns the display while running, so stop it first (pre-authorized
+#    during development). Run scripts/restore-xochitl.sh to bring it back.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+HOST="chatter"
+DEST="/home/root/chatter"   # under /home, NOT the nearly-full rootfs
+
+# Use an explicit binary if given; else a fresh local build; else the prebuilt.
+BIN="${1:-}"
+if [ -z "$BIN" ]; then
+  if [ -f build/chatter ]; then BIN=build/chatter; else BIN=dist/chatter; fi
+fi
+[ -f "$BIN" ] || { echo "binary not found: $BIN (build it, or use the prebuilt dist/chatter)"; exit 1; }
+
+echo ">> stopping any previous chatter + xochitl (release the panel lock)"
+ssh "$HOST" 'systemctl stop chatter 2>/dev/null; systemctl reset-failed chatter 2>/dev/null; systemctl stop xochitl 2>/dev/null; sleep 1'
+
+echo ">> deploying $(basename "$BIN") to $HOST:$DEST"
+ssh "$HOST" "mkdir -p $DEST"
+scp "$BIN" "$HOST:$DEST/"
+
+echo ">> launching chatter as a transient systemd service"
+# LD_LIBRARY_PATH lets the loader resolve libqsgepaper.so (linked for the private
+# EPScreenModeItem type), which lives in the scenegraph plugin dir.
+ssh "$HOST" "systemd-run --unit=chatter --collect \
+  --setenv=QT_QUICK_BACKEND=epaper \
+  --setenv=LD_LIBRARY_PATH=/usr/lib/plugins/scenegraph \
+  --working-directory=$DEST \
+  $DEST/$(basename "$BIN") -platform epaper"
+
+sleep 4
+ssh "$HOST" 'echo "chatter: $(systemctl is-active chatter)"'
+echo ">> logs: ssh chatter 'journalctl -u chatter -f'"
+echo ">> stop:  ssh chatter 'systemctl stop chatter'  (then scripts/restore-xochitl.sh)"

scripts/install-launcher.sh

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+#!/usr/bin/env bash
+# Persistently install the chatter-launcher systemd service ON THE DEVICE.
+#
+# Why this is needed: on the reMarkable Paper Pro Move, /etc and /run are
+# VOLATILE overlays (upperdir on tmpfs) — units placed there are lost on reboot.
+# The root partition is read-only but persistent, so we remount it rw and place
+# the unit (and its enable symlink) under /usr/lib/systemd/system, which survives
+# reboots. (An OS update replaces the rootfs and would require re-running this.)
+#
+# Uses the prebuilt dist/chatter-launcher if present, else a locally built one.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+HOST="${1:-chatter}"
+
+LAUNCHER=dist/chatter-launcher
+[ -f "$LAUNCHER" ] || LAUNCHER=tools/chatter-launcher
+[ -f "$LAUNCHER" ] || { echo "launcher binary not found (dist/ or tools/) — run scripts/build.sh"; exit 1; }
+
+scp -q "$LAUNCHER" "$HOST:/home/root/chatter/chatter-launcher"
+scp -q scripts/to-chatter.sh scripts/chatter-launcher.service "$HOST:/home/root/chatter/"
+
+ssh "$HOST" '
+  set -e
+  chmod +x /home/root/chatter/chatter-launcher /home/root/chatter/to-chatter.sh
+  mount -o remount,rw /
+  cp /home/root/chatter/chatter-launcher.service /usr/lib/systemd/system/chatter-launcher.service
+  mkdir -p /usr/lib/systemd/system/multi-user.target.wants
+  ln -sf ../chatter-launcher.service /usr/lib/systemd/system/multi-user.target.wants/chatter-launcher.service
+  sync
+  mount -o remount,ro /
+  systemctl daemon-reload
+  systemctl restart chatter-launcher.service
+  echo "launcher: $(systemctl is-active chatter-launcher)"
+'

scripts/restore-xochitl.sh

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+#!/usr/bin/env bash
+# Bring the standard reMarkable GUI back after running Chatter.
+set -euo pipefail
+ssh chatter 'systemctl stop chatter 2>/dev/null; systemctl reset-failed chatter 2>/dev/null; systemctl start xochitl'
+echo "chatter stopped; xochitl restarted — standard GUI restored."

scripts/to-chatter.sh

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+#!/bin/sh
+# Switch from the standard interface to Chatter (invoked by the launcher daemon
+# on the multi-finger gesture). Lives on the device at /home/root/chatter/.
+systemctl stop xochitl 2>/dev/null
+systemctl stop chatter 2>/dev/null
+systemctl reset-failed chatter 2>/dev/null
+sleep 1
+systemd-run --unit=chatter --collect \
+  --setenv=QT_QUICK_BACKEND=epaper \
+  --setenv=LD_LIBRARY_PATH=/usr/lib/plugins/scenegraph \
+  --working-directory=/home/root/chatter \
+  /home/root/chatter/chatter -platform epaper