make build-bin: binary uses the system loader on Linux (closes #240)

nix's bun loads through a glibc in the nix store, and bun build --compile
copied that loader into ~/bin/quak, so nix-collect-garbage could break the
cron backup. On Linux x86-64 the build now passes
--target=bun-linux-x64-baseline, which makes bun use its downloaded release
build with the system loader. Other Linux architectures are refused, since
the fix is untested there; macOS is unchanged.

Model: opus-5-5

Makefile

@@ -28,8 +28,20 @@ build:
 
 # Bundles the built dist/, so the binary reports the version script/build
 # stamped.
+#
+# On Linux, nix's bun loads through a C library in the nix store, and a binary
+# bun compiles from itself keeps that loader. nix-collect-garbage can delete
+# that C library, and the binary then no longer starts.
+# A --target other than the host's makes bun use its downloaded release build,
+# which loads through the system's C library. That is tested only on x86-64,
+# with the baseline build, so other Linux machines are refused.
 build-bin: build
-	nix-shell -p bun --run "bun build dist/bin/quak.js --compile --outfile bin/quak"
+	case "$$(uname -s)-$$(uname -m)" in \
+	    Linux-x86_64) target=--target=bun-linux-x64-baseline ;; \
+	    Linux-*) echo "make build-bin: on Linux only x86-64 is supported" >&2; exit 1 ;; \
+	    *) target= ;; \
+	esac; \
+	nix-shell -p bun --run "bun build dist/bin/quak.js --compile $$target --outfile bin/quak"
 
 install: build-bin
 	mkdir -p ~/bin