diff --git a/Examples/HelloPlaydate/README.md b/Examples/HelloPlaydate/README.md
index 1f72997..d1e1d6f 100644
--- a/Examples/HelloPlaydate/README.md
+++ b/Examples/HelloPlaydate/README.md
@@ -18,6 +18,21 @@ The script compiles the game as a dylib, places it in `Source/` next to
 
 ## Device builds
 
-Running on hardware requires the Embedded Swift + ARM toolchain pipeline
-(see the repository README and Apple's swift-playdate-examples for the
-Makefile setup). This example covers the simulator workflow only.
+The Makefile cross-compiles the game with Embedded Swift and packages a
+`HelloPlaydate.pdx` containing both the device binary and the simulator
+dylib. It needs:
+
+- the Playdate SDK (`PLAYDATE_SDK_PATH`, or the path in `~/.Playdate/config`),
+- the Arm GNU toolchain (`arm-none-eabi-gcc`) on `PATH`,
+- a swift.org development-snapshot toolchain (Xcode's toolchain does not
+  ship the Embedded Swift stdlib for the device target). A toolchain
+  installed at `~/Library/Developer/Toolchains` is picked up automatically;
+  otherwise pass `TOOLCHAINS=<bundle id>`.
+
+```sh
+make
+```
+
+Swift code is compiled with `-Osize` by default; use `make SWIFT_OPT=-O` to
+favor speed over size. Sideload the pdx from the Playdate Simulator
+(Device > Upload Game to Device) or with the SDK's `pdutil`.
diff --git a/Examples/HelloPlaydate/Source/pdex.elf b/Examples/HelloPlaydate/Source/pdex.elf
index c35103c..60986fe 100755
Binary files a/Examples/HelloPlaydate/Source/pdex.elf and b/Examples/HelloPlaydate/Source/pdex.elf differ
diff --git a/Examples/swift.mk b/Examples/swift.mk
index a050895..3cd2c60 100644
--- a/Examples/swift.mk
+++ b/Examples/swift.mk
@@ -4,7 +4,7 @@ STACK_SIZE     = 61800
 # Locate the Playdate SDK
 SDK = ${PLAYDATE_SDK_PATH}
 ifeq ($(SDK),)
-SDK = $(shell egrep '^\s*SDKRoot' ~/.Playdate/config | head -n 1 | cut -c9-)
+SDK = $(shell sed -nE 's/^[[:space:]]*SDKRoot[[:space:]]+//p' ~/.Playdate/config | head -n 1)
 endif
 
 ifeq ($(SDK),)
@@ -28,18 +28,37 @@ else
 $(error Swift toolchain not found; set ENV value TOOLCHAINS (e.g. TOOLCHAINS=org.swift.59202403121a make))
 endif
 
+# Note: paths containing spaces are not supported (make word-splits them).
 GCC_INCLUDE_PATHS := $(shell $(CC) -E -Wp,-v -xc /dev/null 2>&1 | egrep '^ ' | xargs echo )
+ifeq ($(GCC_INCLUDE_PATHS),)
+$(error arm-none-eabi C headers not found; install the Arm GNU toolchain and ensure $(CC) is runnable)
+endif
+
 SWIFT_EXEC := "$(shell TOOLCHAINS=$(TOOLCHAINS) xcrun -f swiftc)"
+# With an unknown TOOLCHAINS id, xcrun silently falls back to Xcode's swiftc,
+# which lacks the Embedded ARM stdlib; fail early with a clear message.
+ifeq ($(findstring .xctoolchain,$(SWIFT_EXEC)),)
+$(error swiftc for toolchain "$(TOOLCHAINS)" not found (xcrun returned $(SWIFT_EXEC)); install a swift.org toolchain or set TOOLCHAINS)
+endif
 TOOLCHAIN_PATH := $(shell echo $(SWIFT_EXEC)|sed s'/.xctoolchain.*/.xctoolchain/')
 
 $(info Using Swift toolchain "$(TOOLCHAINS)" (from $(TOOLCHAIN_PATH)))
 
+# Optimization mode for Swift compiles. -Osize targets small code, which
+# suits the device's flash/RAM budget (measured 15% smaller than -O on the
+# HelloPlaydate example); override per-build for maximum speed instead:
+# `make SWIFT_OPT=-O`. For larger games, appending
+# `-Xfrontend -mergeable-symbols -Xfrontend -mergeable-traps` lets the
+# linker deduplicate stdlib code specialized into both the wrapper and the
+# game module.
+SWIFT_OPT ?= -Osize
+
 C_FLAGS := \
 	$(addprefix -I ,$(GCC_INCLUDE_PATHS)) \
 
 SWIFT_FLAGS := \
 	$(addprefix -Xcc , $(C_FLAGS)) \
-	-O \
+	$(SWIFT_OPT) \
 	-wmo -enable-experimental-feature Embedded \
 	-Xfrontend -disable-stack-protector \
 	-Xfrontend -function-sections \
diff --git a/Scripts/build-embedded.sh b/Scripts/build-embedded.sh
index 9084622..d75769d 100755
--- a/Scripts/build-embedded.sh
+++ b/Scripts/build-embedded.sh
@@ -50,6 +50,7 @@ exec "$swift_bin" build \
     --triple armv7em-none-none-eabi \
     -Xswiftc -enable-experimental-feature -Xswiftc Embedded \
     -Xswiftc -wmo \
+    -Xswiftc -Osize \
     -Xcc -I"$include_dir" \
     -Xcc -mcpu=cortex-m7 \
     -Xcc -mfloat-abi=hard \
diff --git a/Sources/PlayDate/GraphicsVideo.swift b/Sources/PlayDate/GraphicsVideo.swift
index 5f65b5f..eb71767 100644
--- a/Sources/PlayDate/GraphicsVideo.swift
+++ b/Sources/PlayDate/GraphicsVideo.swift
@@ -60,7 +60,10 @@ extension Graphics {
         /// Renders frame `frame` into the current context.
         public func renderFrame(_ frame: Int) throws(PlaydateError) {
             guard videoAPI.pointee.renderFrame.unsafelyUnwrapped(pointer, Int32(frame)) != 0 else {
-                throw PlaydateError(message: error ?? "unable to render frame \(frame)")
+                // Static message: the caller knows the frame it passed, and
+                // interpolating it would pull integer formatting machinery
+                // into the device binary.
+                throw PlaydateError(message: error ?? "unable to render frame")
             }
         }
 
diff --git a/Sources/PlayDate/JSON.swift b/Sources/PlayDate/JSON.swift
index 9af6f13..2590a66 100644
--- a/Sources/PlayDate/JSON.swift
+++ b/Sources/PlayDate/JSON.swift
@@ -170,8 +170,10 @@ extension JSON {
         return try decode(file: file)
     }
 
+    // Static message: interpolating the line number would pull integer
+    // formatting machinery into every device binary that decodes JSON.
     private static func decodeError(_ context: DecodeContext) -> PlaydateError {
-        PlaydateError(message: "\(context.errorMessage ?? "JSON decode failed") (line \(context.errorLine))")
+        PlaydateError(message: context.errorMessage ?? "JSON decode failed")
     }
 
     // MARK: - Encoding