diff --git a/GAME.md b/GAME.md
index 63d045d..859d3a4 100644
--- a/GAME.md
+++ b/GAME.md
@@ -355,7 +355,6 @@ src/
 ├── draw.c / .h         # the white-screen + counter rendering
 ├── rasterirq.c / .h    # 50 Hz frame tick
 ├── notes.h             # SID frequency table
-├── build.sh            # (already exists)
 └── build/              # (gitignored) output
 ```
 
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..4ce5f5f
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,234 @@
+# nyuller — C64 game (Oscar64 cross-compiler)
+# ============================================================
+# GNU Make wrapper for building and running via oscar64 / VICE.
+#
+# Default target: help
+
+# --- paths -------------------------------------------------
+ROOT       := $(abspath $(dir $(lastword $(MAKEFILE_LIST))))
+OSCAR64_DIR := $(ROOT)/oscar64
+OSCAR64_BIN := $(OSCAR64_DIR)/bin/oscar64
+BUILD_DIR  := $(ROOT)/build
+
+SRC        := main.c
+PRG        := $(BUILD_DIR)/nyuller.prg
+D64        := $(BUILD_DIR)/nyuller.d64
+LOG        := $(BUILD_DIR)/vice.log
+PID_FILE   := $(BUILD_DIR)/vice.pid
+SRC_DIR    := $(ROOT)/src
+
+# --- oscar64 flags ----------------------------------------
+# Override with:  make OPT=O3    (or O0/O1/O2/Os/g)
+OPT          ?= O1
+OPT_FLAGS    := -$(OPT)
+
+# --- VICE flags -------------------------------------------
+VICE_FLAGS   := +confirmonexit -drive8type 1541
+
+# --- phony targets ----------------------------------------
+.PHONY: help compile run run-vice run-vice-cycle-exact \
+        play play-cycle-exact kill clean ensure-build-dir
+
+# ============================================================
+# help (default)
+# ============================================================
+help:
+	@echo ""
+	@echo "  nyuller — C64 game (Oscar64 cross-compiler)"
+	@echo "  ──────────────────────────────────────────────"
+	@echo ""
+	@echo "  Compile"
+	@echo "    make                    compile main.c → build/nyuller.prg (-O1)"
+	@echo "    make compile            same as above"
+	@echo "    make OPT=O3             compile with -O3 (release build)"
+	@echo "    make OPT=O0             compile with -O0 (debug build)"
+	@echo "    make OPT=Os             compile with -Os (optimize for size)"
+	@echo ""
+	@echo "  Run"
+	@echo "    make run                compile + run in oscar64 emulator (headless, fast)"
+	@echo "    make run-vice           compile + run in VICE x64 (foreground, blocks)"
+	@echo "    make run-vice-cycle     compile + run in VICE x64sc (cycle-exact, slow)"
+	@echo ""
+	@echo "  Play (detached — returns to shell)"
+	@echo "    make play               compile + launch VICE x64 in background"
+	@echo "    make play-cycle         compile + launch VICE x64sc in background"
+	@echo "    make kill               kill any running detached VICE"
+	@echo ""
+	@echo "  Clean"
+	@echo "    make clean              remove build/ artifacts and VICE log/pid files"
+	@echo ""
+	@echo "  Output (in build/)"
+	@echo "    nyuller.prg             loadable C64 program"
+	@echo "    nyuller.d64             disk image wrapping nyuller.prg (for VICE autostart)"
+	@echo "    nyuller.asm             full 6502 listing"
+	@echo "    nyuller.map             region/section/object placement"
+	@echo "    nyuller.lbl             VICE monitor label commands"
+	@echo ""
+	@echo "  VICE note: -drive8type 1541 is required for autostart to work."
+	@echo "  Without this flag the autostart LOAD\"*\",8,1 fails with ?DEVICE"
+	@echo "  NOT PRESENT.  We have the original 1541 ROM installed at:"
+	@echo "    ~/.local/share/vice/DRIVES/dos1541-325302-01+901229-05.bin"
+	@echo ""
+	@echo "  Default joystick keys in VICE (rebindable under Settings):"
+	@echo "    Port 2 (left, Scoot)  W/A/S/D + Left Ctrl (fire)"
+	@echo "    Port 1 (right, Hare)  Arrows  + Right Shift (fire)"
+	@echo ""
+
+# ============================================================
+# ensure-build-dir
+# ============================================================
+ensure-build-dir:
+	@mkdir -p "$(BUILD_DIR)"
+
+# ============================================================
+# compile
+# ============================================================
+compile: ensure-build-dir
+	@# Build the oscar64 compiler first if it doesn't exist.
+	@if [ ! -x "$(OSCAR64_BIN)" ]; then \
+		echo "oscar64 compiler not found at $(OSCAR64_BIN); building it..."; \
+		cd "$(OSCAR64_DIR)" && make -C make compiler; \
+	fi
+	@if [ ! -x "$(OSCAR64_BIN)" ]; then \
+		echo "error: $(OSCAR64_BIN) is still missing after build" >&2; \
+		echo "  try: cd $(OSCAR64_DIR) && make -C make compiler" >&2; \
+		exit 1; \
+	fi
+	@echo "compiling $(SRC) with $(OSCAR64_BIN) -> $(BUILD_DIR)/"
+	cd "$(SRC_DIR)" && "$(OSCAR64_BIN)" -i="$(OSCAR64_DIR)/include" -o="$(PRG)" $(OPT_FLAGS) "$(SRC)"
+
+# ============================================================
+# run — oscar64 built-in emulator (headless, fast)
+# ============================================================
+run: ensure-build-dir
+	@if [ ! -x "$(OSCAR64_BIN)" ]; then \
+		echo "oscar64 compiler not found at $(OSCAR64_BIN); building it..."; \
+		cd "$(OSCAR64_DIR)" && make -C make compiler; \
+	fi
+	@if [ ! -x "$(OSCAR64_BIN)" ]; then \
+		echo "error: $(OSCAR64_BIN) is still missing after build" >&2; \
+		echo "  try: cd $(OSCAR64_DIR) && make -C make compiler" >&2; \
+		exit 1; \
+	fi
+	@echo "running $(SRC) in oscar64's built-in emulator"
+	cd "$(SRC_DIR)" && "$(OSCAR64_BIN)" -i="$(OSCAR64_DIR)/include" -o="$(PRG)" $(OPT_FLAGS) -e "$(SRC)"
+
+# ============================================================
+# run-vice — VICE x64 (foreground, blocks terminal)
+# ============================================================
+run-vice: $(D64)
+	@echo "running nyuller in VICE x64 (blocking)"
+	x64 $(VICE_FLAGS) -autostart "$(D64)"
+
+# ============================================================
+# run-vice-cycle — VICE x64sc (foreground, cycle-exact, slow)
+# ============================================================
+run-vice-cycle: $(D64)
+	@echo "running nyuller in VICE x64sc (cycle-exact, blocking)"
+	x64sc $(VICE_FLAGS) -autostart "$(D64)"
+
+# ============================================================
+# play — VICE x64 detached (returns to shell)
+# ============================================================
+play: compile $(D64)
+	@# Kill any previous VICE first.
+	@existing=$$(pgrep -f 'x64(sc)? \+confirmonexit.*nyuller\.d64' 2>/dev/null || true); \
+	if [ -n "$$existing" ]; then \
+		echo "killing previous VICE process(es): $$existing"; \
+		kill $$existing 2>/dev/null || true; \
+		sleep 1; \
+		kill -9 $$existing 2>/dev/null || true; \
+	fi
+	@echo "launching VICE x64 in the background with $(D64)..."
+	@setsid nohup x64 $(VICE_FLAGS) -autostart "$(D64)" \
+		> "$(LOG)" 2>&1 < /dev/null & echo $$! > "$(PID_FILE)"
+	@sleep 1
+	@if kill -0 "$$(cat "$(PID_FILE)")" 2>/dev/null; then \
+		echo ""; \
+		echo "VICE launched (PID $$(cat "$(PID_FILE)")). Look for the x64 window on your desktop."; \
+		echo "Default keys: Port 1 (Hare)  = Arrows + Right Shift (fire)"; \
+		echo "             Port 2 (Scoot) = W A S D + Left Ctrl (fire)"; \
+		echo "Rebind under Settings → Input devices → Joystick settings."; \
+		echo "To stop VICE later:  make kill"; \
+		echo "Log file: $(LOG)"; \
+	else \
+		echo "error: VICE failed to start; see $(LOG) for details" >&2; \
+		exit 1; \
+	fi
+
+# ============================================================
+# play-cycle — VICE x64sc detached (cycle-exact, returns to shell)
+# ============================================================
+play-cycle: compile $(D64)
+	@existing=$$(pgrep -f 'x64(sc)? \+confirmonexit.*nyuller\.d64' 2>/dev/null || true); \
+	if [ -n "$$existing" ]; then \
+		echo "killing previous VICE process(es): $$existing"; \
+		kill $$existing 2>/dev/null || true; \
+		sleep 1; \
+		kill -9 $$existing 2>/dev/null || true; \
+	fi
+	@echo "launching VICE x64sc in the background with $(D64)..."
+	@setsid nohup x64sc $(VICE_FLAGS) -autostart "$(D64)" \
+		> "$(LOG)" 2>&1 < /dev/null & echo $$! > "$(PID_FILE)"
+	@sleep 1
+	@if kill -0 "$$(cat "$(PID_FILE)")" 2>/dev/null; then \
+		echo ""; \
+		echo "VICE launched (PID $$(cat "$(PID_FILE)")). Look for the x64sc window on your desktop."; \
+		echo "Default keys: Port 1 (Hare)  = Arrows + Right Shift (fire)"; \
+		echo "             Port 2 (Scoot) = W A S D + Left Ctrl (fire)"; \
+		echo "Rebind under Settings → Input devices → Joystick settings."; \
+		echo "To stop VICE later:  make kill"; \
+		echo "Log file: $(LOG)"; \
+	else \
+		echo "error: VICE failed to start; see $(LOG) for details" >&2; \
+		exit 1; \
+	fi
+
+# ============================================================
+# kill — stop any detached VICE
+# ============================================================
+kill:
+	@# pgrep -f uses ERE: + is a quantifier, so the regex must escape it.
+	@# x64(sc)? matches both "x64" and "x64sc".  The process is launched
+	@# with the literal argument string `+confirmonexit`.
+	@pids=$$(pgrep -f 'x64(sc)? \+confirmonexit.*nyuller\.d64' 2>/dev/null || true); \
+	if [ -n "$$pids" ]; then \
+		echo "killing VICE process(es): $$pids"; \
+		kill $$pids 2>/dev/null || true; \
+		sleep 1; \
+		kill -9 $$pids 2>/dev/null || true; \
+	else \
+		echo "no VICE process running (autostart of nyuller.d64)"; \
+	fi
+	@rm -f "$(PID_FILE)" "$(LOG)"
+
+# ============================================================
+# $(D64) — build the .d64 disk image from the .prg
+# ============================================================
+# c1541's exit code is unreliable (the interactive form always
+# exits 0 even on failure), so the only reliable success signal
+# is listing the disk afterwards and checking the PRG is there.
+# The flag-form `c1541 -list image` doesn't work (c1541 treats
+# it as a unit number), so we use the interactive heredoc form.
+# All c1541 calls are wrapped in `|| true` so the final
+# list-and-grep is the authoritative check.
+$(D64): $(PRG) | ensure-build-dir
+	@echo "wrapping $(PRG) in $(D64) (VICE autostart needs a disk image)..."
+	@c1541 -format ny,of d64 "$(D64)" >/dev/null 2>&1 || true
+	@echo "write $(PRG)" | c1541 "$(D64)" >/dev/null 2>&1 || true
+	@if printf "list\nquit\n" | c1541 "$(D64)" 2>/dev/null | grep -q "nyuller.prg"; then \
+		:; \
+	else \
+		echo "error: failed to write $(PRG) to $(D64) (c1541 silently exited 0)" >&2; \
+		rm -f "$(D64)"; \
+		exit 1; \
+	fi
+
+# ============================================================
+# clean
+# ============================================================
+clean:
+	rm -f "$(PRG)" "$(D64)" "$(BUILD_DIR)/nyuller.asm" "$(BUILD_DIR)/nyuller.map" \
+		"$(BUILD_DIR)/nyuller.lbl" "$(BUILD_DIR)/nyuller.int" "$(BUILD_DIR)/nyuller.dbj" \
+		"$(BUILD_DIR)/nyuller.csz" "$(PID_FILE)" "$(LOG)"
+	@echo "cleaned build/"
diff --git a/README.md b/README.md
index 69e7939..b586ad5 100644
--- a/README.md
+++ b/README.md
@@ -12,8 +12,8 @@ as the cross-compiler. Oscar64 is checked in as a git submodule under
 ├── build/          # Build output (gitignored)
 ├── docs/c64/       # Low-level C64 reference (memory map, VIC, CIA, SID, …)
 ├── src/            # Your C code
-│   ├── helloworld.c
-│   └── build.sh    # Compile + run helper
+│   └── *.c, *.h
+├── Makefile        # Build + run targets (gnu make)
 ├── OSCAR64.md      # Notes on the Oscar64 compiler internals
 └── PROG_C64.md     # Notes on programming the C64 hardware
 ```
@@ -31,28 +31,28 @@ git submodule update --init --recursive
 ## Building
 
 ```sh
-cd src
-./build.sh            # compile main.c → build/nyuller.prg (-O1)
-./build.sh -e         # run in oscar64's built-in emulator (headless, fast)
-./build.sh -p         # PLAY: launch VICE in background (see build.sh --help)
-./build.sh -v         # run in VICE x64 (foreground, blocks terminal)
-./build.sh -V         # run in VICE x64sc (cycle-exact, foreground)
-./build.sh --kill     # kill any detached VICE process
-./build.sh -c         # just compile
-./build.sh -O3        # release build (auto-ZP, outliner, aggressive inlining)
+make                    # show help with all targets
+make compile            # compile → build/nyuller.prg (-O1)
+make run                # compile + run in oscar64 emulator (headless, fast)
+make play               # compile + launch VICE x64 in background
+make kill               # kill any detached VICE
+make OPT=O3             # release build (auto-ZP, outliner, aggressive inlining)
+make clean              # remove build/ artifacts
 ```
 
-`build.sh` will build the oscar64 compiler automatically the first time
+`make` will build the oscar64 compiler automatically the first time
 (it runs `make -C make compiler` inside `./oscar64/` if
 `./oscar64/bin/oscar64` doesn't exist yet).
 
-**Default test tool is the oscar64 built-in emulator** (`-e`): it
+Run `make help` for the full list of targets with descriptions.
+
+**Default test tool is the oscar64 built-in emulator** (`make run`): it
 runs headless, needs no ROMs, no display, and is fast. Every `Verify`
 step in `tasks.md` uses this.
 
 **VICE 3.9 is installed** at `/usr/bin/` (`x64`, `x64sc`, `x128`,
-`xvic`, `xpet`) and is available via `-v` / `-V`. It is a GUI
-emulator and **needs a real X11 / Wayland display to render** — it
+`xvic`, `xpet`) and is available via `make run-vice` / `make run-vice-cycle`.
+It is a GUI emulator and **needs a real X11 / Wayland display to render** — it
 won't produce useful screenshots in this headless environment.
 Use it from a real terminal session for interactive play-testing
 and cycle-exact validation of raster IRQ and SID timing; don't
diff --git a/src/AGENT_CONTEXT.md b/src/AGENT_CONTEXT.md
index 008c7d0..4ba904c 100644
--- a/src/AGENT_CONTEXT.md
+++ b/src/AGENT_CONTEXT.md
@@ -28,29 +28,30 @@ context you need to do the work.
 ├── source_images/          # The 5 source PNGs for the game screens
 └── src/                    # YOUR CODE GOES HERE
     ├── helloworld.c        # Existing minimal working program
-    ├── build.sh            # Build script (handles compiler build, runs tests)
+    ├── build.sh            # Legacy build script (replaced by Makefile)
     └── build/              # Output directory (gitignored)
 ```
 
 ## Build and test (this is the ONLY way to verify your work)
 
 ```sh
-cd /home/ballz/work/teletype/nyuller/src
-./build.sh                 # compile helloworld.c → build/helloworld.prg
-./build.sh -e              # run in oscar64's built-in emulator (HEADLESS, fast)
-./build.sh -v              # (DO NOT USE) VICE x64 — requires a real display
-./build.sh -V              # (DO NOT USE) VICE x64sc — same problem
+cd /home/ballz/work/teletype/nyuller
+make                     # show help with all targets
+make compile             # compile → build/nyuller.prg
+make run                 # compile + run in oscar64 emulator (HEADLESS, fast)
+make play                # compile + launch VICE in background
+make kill                # kill any detached VICE
 ```
 
-**The oscar64 built-in emulator (`-e`) is the only test tool.** VICE
+**The oscar64 built-in emulator (`make run`) is the only test tool.** VICE
 does not work in this headless environment (no display, blank
 screenshots, manual ROM fetching). Do not waste time on VICE.
-The `-e` flag runs the same `.prg` file the C64 will run, with no
+The `run` target runs the same `.prg` file the C64 will run, with no
 setup, no ROMs, and at high speed.
 
-`build.sh` will auto-build the oscar64 compiler if it's missing.
-It calls `oscar64 -i=/home/ballz/work/teletype/nyuller/oscar64/include -o=build/helloworld.prg helloworld.c`
-to compile, and the same command with `-e` to run.
+`make` will auto-build the oscar64 compiler if it's missing.
+It runs `cd src && oscar64 -i=…/include -o=…/build/nyuller.prg main.c`
+to compile, and `cd src && oscar64 -i=…/include -o=…/build/nyuller.prg -e main.c` to run.
 
 The build artifacts in `build/` are: `helloworld.prg` (the C64 program),
 `helloworld.asm` (6502 listing), `helloworld.map` (region/section/object
@@ -180,6 +181,6 @@ $21-$24) goes to $D800-$DBE7.
 
 When you're done, report back:
 1. What you built (1-2 sentence summary)
-2. The output of `./build.sh -e` (proves it compiled and runs)
+2. The output of `make run` (proves it compiled and runs)
 3. The git commit hash and one-line summary
 4. Any concerns or follow-up work for the next phase
diff --git a/src/build.sh b/src/build.sh
deleted file mode 100755
index 993c4c4..0000000
--- a/src/build.sh
+++ /dev/null
@@ -1,217 +0,0 @@
-#!/bin/sh
-# build.sh — compile and optionally run a single C64 program with Oscar64.
-#
-# Usage:
-#   ./build.sh            # compile main.c → build/nyuller.prg (-O1)
-#   ./build.sh -e         # run in oscar64's built-in emulator (headless, fast)
-#   ./build.sh -p         # PLAY: compile, wrap in .d64, launch VICE x64 detached
-#   ./build.sh -P         # PLAY: same as -p but with VICE x64sc (cycle-exact)
-#   ./build.sh -v         # run in VICE x64 (foreground, blocks terminal)
-#   ./build.sh -V         # run in VICE x64sc (foreground, blocks terminal)
-#   ./build.sh --kill     # kill any running VICE x64/x64sc process
-#   ./build.sh -c         # just compile
-#   ./build.sh -O0        # compile with -O0 (no optimization; debug build)
-#   ./build.sh -O2        # compile with -O2 (more aggressive inlining)
-#   ./build.sh -O3        # compile with -O3 (release build; auto-ZP, outliner)
-#   ./build.sh -Os        # compile with -Os (optimize for size)
-#   ./build.sh -g         # compile with -g (adds source-level debug info)
-#
-# Output (in <repo>/build/):
-#   nyuller.prg        — loadable C64 program (run with x64, VICE, or real hw)
-#   nyuller.asm        — full 6502 listing
-#   nyuller.map        — region/section/object placement
-#   nyuller.lbl        — VICE monitor label commands
-#   nyuller.d64        — disk image wrapping nyuller.prg (for VICE autostart)
-#
-# VICE note: -drive8type 1541 is required for autostart to work.  VICE
-# defaults to the 1541-II (drive type 1542), whose ROM we don't have
-# installed; without this flag the autostart `LOAD"*",8,1` fails with
-# ?DEVICE NOT PRESENT.  We have the original 1541 ROM at
-# ~/.local/share/vice/DRIVES/dos1541-325302-01+901229-05.bin.
-#
-# For the development loop, use -e (oscar64's built-in emulator). It runs
-# without a display, needs no ROMs, and is faster than VICE. Use -p when
-# you want to play the game interactively — it launches VICE in the
-# background and returns control to your shell so you can do other things.
-#
-# Default joystick keys in VICE (Settings → Input devices → Joystick
-# settings to rebind if needed):
-#   Port 2 (left, Scoot):  W/A/S/D for up/left/right/down, Left Ctrl for fire
-#   Port 1 (right, Hare):  Arrow keys for up/left/right/down, Right Shift for fire
-# (You can rebind under Settings → Input devices → Joystick settings.)
-#
-# Optimization: the default is oscar64's default (-O1).  Pass -O3 to
-# produce a release build (auto-zero-page, outliner, aggressive inlining).
-# The release build is functionally identical to the default build on
-# cycle-accurate timings — the audio and frame counters are still
-# 50 Hz because they use the raster IRQ, not CPU-bound loops.
-
-set -e
-
-# --- locate the oscar64 compiler -----------------------------------------
-SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
-OSCAR64_DIR="$ROOT/oscar64"
-OSCAR64_BIN="$OSCAR64_DIR/bin/oscar64"
-BUILD_DIR="$ROOT/build"
-PRG="$BUILD_DIR/nyuller.prg"
-D64="$BUILD_DIR/nyuller.d64"
-
-mkdir -p "$BUILD_DIR"
-
-# --- kill any running VICE ------------------------------------------------
-if [ "${1:-}" = "--kill" ]; then
-	# pgrep -f uses ERE: + is a quantifier, so the regex must escape it.
-	# x64(sc)? matches both "x64" and "x64sc".  The process is launched
-	# with the literal argument string `+confirmonexit`.
-	pids=$(pgrep -f "x64(sc)? \+confirmonexit.*nyuller\.d64" 2>/dev/null || true)
-	if [ -n "$pids" ]; then
-		echo "killing VICE process(es): $pids"
-		kill $pids 2>/dev/null || true
-		sleep 1
-		kill -9 $pids 2>/dev/null || true
-	else
-		echo "no VICE process running (autostart of nyuller.d64)"
-	fi
-	rm -f "$BUILD_DIR/vice.pid" "$BUILD_DIR/vice.log"
-	exit 0
-fi
-
-# Build the compiler if it's missing.
-if [ ! -x "$OSCAR64_BIN" ]; then
-	echo "oscar64 compiler not found at $OSCAR64_BIN; building it..."
-	( cd "$OSCAR64_DIR" && make -C make compiler )
-fi
-
-if [ ! -x "$OSCAR64_BIN" ]; then
-	echo "error: $OSCAR64_BIN is still missing after build" >&2
-	echo "  try: cd $OSCAR64_DIR && make -C make compiler" >&2
-	exit 1
-fi
-
-# --- parse args -----------------------------------------------------------
-SRC=main.c
-EMU_CMD=""
-PLAY_VICE=""
-OPT_FLAGS=""
-
-for arg in "$@"; do
-	case "$arg" in
-		-e) EMU_CMD="oscar64" ;;
-		-v) EMU_CMD="x64" ;;
-		-V) EMU_CMD="x64sc" ;;
-		-p) PLAY_VICE="x64" ;;
-		-P) PLAY_VICE="x64sc" ;;
-		-c) ;;
-		-O0) OPT_FLAGS="$OPT_FLAGS -O0" ;;
-		-O1) OPT_FLAGS="$OPT_FLAGS -O1" ;;
-		-O2) OPT_FLAGS="$OPT_FLAGS -O2" ;;
-		-O3) OPT_FLAGS="$OPT_FLAGS -O3" ;;
-		-Os) OPT_FLAGS="$OPT_FLAGS -Os" ;;
-		-g)  OPT_FLAGS="$OPT_FLAGS -g"  ;;
-		-*) echo "unknown flag: $arg" >&2; exit 1 ;;
-	esac
-done
-
-# Reject conflicting flag combinations: -v/-V (foreground VICE) and
-# -p/-P (background VICE) would both fire, leaving two emulator windows.
-if [ -n "$EMU_CMD" ] && [ -n "$PLAY_VICE" ]; then
-	echo "error: cannot combine a foreground VICE flag (-v/-V) with a play flag (-p/-P)" >&2
-	echo "  use -v to run in the foreground, or -p to detach and continue" >&2
-	exit 1
-fi
-
-# --- compile --------------------------------------------------------------
-echo "compiling $SRC with $OSCAR64_BIN -> $BUILD_DIR/"
-"$OSCAR64_BIN" -i="$OSCAR64_DIR/include" -o="$PRG" $OPT_FLAGS "$SRC"
-
-# build_d64() — wrap $PRG in $D64.  c1541's exit code is unreliable
-# (the interactive form always exits 0 even on failure), so the only
-# reliable success signal is listing the disk afterwards and checking
-# the PRG is there.  The flag-form `c1541 -list image` doesn't work
-# (c1541 treats it as a unit number), so we use the interactive
-# heredoc form.  All c1541 calls are wrapped in `|| true` so set -e
-# doesn't trip on transient non-zero exits from the format / write
-# steps; the final list-and-grep is the authoritative check.
-build_d64() {
-	if ! command -v c1541 >/dev/null 2>&1; then
-		echo "error: c1541 not found (needed to build the .d64 wrapper)" >&2
-		return 1
-	fi
-	c1541 -format ny,of d64 "$D64" >/dev/null 2>&1 || true
-	c1541 "$D64" >/dev/null 2>&1 <<EOF || true
-write $PRG
-EOF
-	if c1541 "$D64" 2>/dev/null <<EOF | grep -q "nyuller.prg"
-list
-quit
-EOF
-	then
-		:
-	else
-		echo "error: failed to write $PRG to $D64 (c1541 silently exited 0)" >&2
-		return 1
-	fi
-}
-
-# --- optional actions -----------------------------------------------------
-case "$EMU_CMD" in
-	"oscar64")
-		echo "running nyuller.prg in oscar64's built-in emulator"
-		"$OSCAR64_BIN" -i="$OSCAR64_DIR/include" -o="$PRG" $OPT_FLAGS -e "$SRC"
-		;;
-	"x64"|"x64sc")
-		echo "wrapping $PRG in $D64 (VICE autostart needs a disk image)..."
-		build_d64
-		if [ -z "${DISPLAY:-}" ]; then
-			echo "warning: no \$DISPLAY set; VICE won't show a window" >&2
-		fi
-		echo "running nyuller in VICE ($EMU_CMD, blocking)"
-		"$EMU_CMD" +confirmonexit -drive8type 1541 -autostart "$D64"
-		;;
-esac
-
-if [ -n "$PLAY_VICE" ]; then
-	if [ -z "${DISPLAY:-}" ]; then
-		echo "error: no \$DISPLAY set; cannot launch VICE in a window" >&2
-		exit 1
-	fi
-	if ! command -v "$PLAY_VICE" >/dev/null 2>&1; then
-		echo "error: $PLAY_VICE not found in PATH" >&2
-		exit 1
-	fi
-	# If a previous VICE is still running, kill it before launching a
-	# new one — otherwise the two windows will fight for the same
-	# display and the old one's nyuller will keep running in the
-	# background.
-	existing=$(pgrep -f "x64(sc)? \+confirmonexit.*nyuller\.d64" 2>/dev/null || true)
-	if [ -n "$existing" ]; then
-		echo "killing previous VICE process(es): $existing"
-		kill $existing 2>/dev/null || true
-		sleep 1
-		kill -9 $existing 2>/dev/null || true
-	fi
-	echo "wrapping $PRG in $D64 (VICE autostart needs a disk image)..."
-	build_d64
-	echo "launching VICE $PLAY_VICE in the background with $D64..."
-	log="$BUILD_DIR/vice.log"
-	( setsid nohup "$PLAY_VICE" +confirmonexit -drive8type 1541 -autostart "$D64" \
-		> "$log" 2>&1 < /dev/null & echo $! > "$BUILD_DIR/vice.pid" )
-	# setsid + nohup detach VICE from this shell so it survives our exit.
-	pid=$(cat "$BUILD_DIR/vice.pid")
-	sleep 1
-	if kill -0 "$pid" 2>/dev/null; then
-		echo ""
-		echo "VICE launched (PID $pid). Look for the x64 window on your desktop."
-		echo "Default keys: Port 1 (Hare)  = Arrows + Right Shift (fire)"
-		echo "             Port 2 (Scoot) = W A S D + Left Ctrl (fire)"
-		echo "Rebind under Settings → Input devices → Joystick settings."
-		echo "To stop VICE later:  ./build.sh --kill"
-		echo "Log file: $log"
-	else
-		echo "error: VICE failed to start; see $log for details" >&2
-		exit 1
-	fi
-fi
-
-echo "done: $PRG"
diff --git a/src/helloworld.c b/src/helloworld.c
index 597d9c8..118ded4 100644
--- a/src/helloworld.c
+++ b/src/helloworld.c
@@ -2,9 +2,8 @@
 //
 // Builds a .prg that prints "Hello World" on the C64 text screen and exits.
 //
-// Build:  ../scripts/build.sh
-// Run:    x64 helloworld.prg   (or use ../scripts/build.sh -e to run in
-//                              the built-in oscar64 emulator)
+// Build:  make compile
+// Run:    make run
 
 #include <stdio.h>
 
diff --git a/tasks.md b/tasks.md
index fe21ea6..6650eb3 100644
--- a/tasks.md
+++ b/tasks.md
@@ -17,7 +17,7 @@ produces files in `./src/data/`.
 ## 0.1. Test environment
 
 **The oscar64 built-in emulator is the primary test tool.** It's
-invoked with `build.sh -e` (or `oscar64 -i=… -e source.c`) and
+invoked with `make run` (or `oscar64 -i=… -e source.c`) and
 runs the same `.prg` file the C64 will run, with no setup, no
 display, no ROMs, and at high speed. It is the default for the
 development loop and is what every phase's *Verify* step uses.
@@ -28,7 +28,7 @@ In this headless environment, the ROMs had to be fetched manually,
 the KERNAL/BASIC/CHAR/1541 ROMs were not bundled with the package,
 and the autostart mechanism produced blank screenshots (no display
 to render to). We attempted to get VICE working and abandoned
-the effort after deciding it wasn't worth the time. The `build.sh
+the effort after deciding it wasn't worth the time. The `make run`
 -v` / `-V` flags remain in place for the rare case where someone
 has a real terminal session and wants to use VICE interactively,
 but **no phase of this project depends on VICE for verification**,
@@ -36,11 +36,11 @@ and the `-v` / `-V` flags are *optional* additions, not required.
 
 | Tool | Headless? | Use it for |
 |------|-----------|------------|
-| `build.sh -e` (oscar64 built-in) | Yes | Default for every Verify step. Fast, deterministic, runs in CI. |
-| `build.sh -v` / `-V` (VICE) | No | Optional, interactive only. VICE is unreliable in this headless env and not used for verification. |
+| `make run` (oscar64 built-in) | Yes | Default for every Verify step. Fast, deterministic, runs in CI. |
+| `make run-vice` / `make run-vice-cycle` (VICE) | No | Optional, interactive only. VICE is unreliable in this headless env and not used for verification. |
 | `x128` / `xvic` / `xpet` | No | Out of scope (we target C64 PAL). |
 
-**Bottom line for the plan:** every `Verify` step uses `build.sh -e`
+**Bottom line for the plan:** every `Verify` step uses `make run`
 (unless explicitly noted). VICE is referenced only in Phase 8
 (end-to-end testing) and in the optional Phase 9 (NTSC) — both
 of which assume a developer with a real terminal session will run
@@ -64,11 +64,11 @@ the tests.
 runs.
 
 - [x] ✅ Repo initialized, oscar64 is a submodule at `./oscar64/`.
-- [x] ✅ `src/helloworld.c` + `src/build.sh` produce
+- [x] ✅ `src/helloworld.c` + `make compile` produce
   `build/helloworld.prg`.
 - [x] ✅ `GAME.md` written.
 - [x] ✅ Source artwork in `./source_images/`.
-- [ ] ⏳ **Verify:** `cd src && ./build.sh -e` runs the hello-world
+- [ ] ⏳ **Verify:** `cd src && ./make run` runs the hello-world
   program in the oscar64 built-in emulator. (Optional: launch
   `x64 build/helloworld.prg` in a real terminal session
   to see the screen.)
@@ -168,7 +168,7 @@ state.
   pressed (active low: `(PEEK(0xDC00+port) & 0x10) == 0`).
 
 **Verify:**
-- `cd src && ./build.sh -e` displays the title screen in the
+- `cd src && ./make run` displays the title screen in the
   oscar64 built-in emulator for 5 seconds (or until fire is pressed)
   then exits.
 - (Optional, interactive) `x64 build/nyuller.prg` in a real
@@ -303,7 +303,7 @@ random source.
 
 **Verify:**
 - The game still works in the oscar64 built-in emulator
-  (`build.sh -e`).
+  (`make run`).
 - (Optional, interactive) Launch `x64sc build/nyuller.prg`
   in a real terminal to confirm the game runs at cycle-exact PAL
   timing (50.125 Hz). The state transitions happen on the right
@@ -432,7 +432,7 @@ with no rough edges. We also do the real-hardware test.
   transition. Just a quick low square wave.
 - [ ] Make sure scores are reset on entering GAMEOVER → TITLE.
 - [ ] Run the full game in the oscar64 built-in emulator
-  (`build.sh -e`) for the development loop, and (optionally,
+  (`make run`) for the development loop, and (optionally,
   when you have a real terminal session) in `x64` / `x64sc` for
   interactive play-testing and cycle-exact validation. Coverage:
   - P1 wins 5 in a row (cheat test: hold fire on port 1 the
@@ -449,8 +449,8 @@ with no rough edges. We also do the real-hardware test.
 - [ ] If we have a real C64 or a Turbo Everdrive, test on
   real hardware. Otherwise document that we tested in the
   oscar64 emulator + `x64sc` cycle-exact mode.
-- [ ] Strip `-g` from the release build. Add a `-O3` build
-  target to build.sh.
+- [ ] Strip `-g` from the release build. Add a `make OPT=O3` build
+  target to Makefile (already supported via `make compile OPT=O3`).
 - [ ] Final pass: review the .map file, check no section is
   larger than expected, check no RAM region is over-allocated.
 - [ ] Final sanity check: load the release build into `x64sc`