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

README.md

@@ -138,7 +138,10 @@ requests. The "Library reference" below covers both.
 one binary and copies it to `~/bin/quak`. Besides what Getting Started needs,
 `make install` needs `make` and [nix](https://nixos.org/download). It uses bun,
 a JavaScript runtime, to bundle the built `dist/` into one executable. It runs
-bun through `nix-shell -p bun`.
+bun through `nix-shell -p bun`. On Linux it works on x86-64 only. There, the
+binary is built from bun's own release build rather than nix's bun, so it does
+not need the nix store. The first build downloads that release build into
+`~/.bun`.
 
 Log in once with `~/bin/quak`, as the user the cron job will run as:
 
@@ -671,9 +674,6 @@ but letters and digits, or when it is longer than 16 characters.
 When the date or the time zone changes, the next run stores the original at its
 new path and leaves the old copy where it is.
 
-A file deleted in Ente keeps its original at its save path, and the JSON beside
-it. The next run removes its symlinks from the collection directories.
-
 The library gives the same path as `photo.savePath` and writes it with
 `photo.download()` (see "A photo's content").
 
@@ -1913,7 +1913,8 @@ These apply to people and to coding agents alike.
       `bin/clip-keyword-vectors` installs, by SHA-256 hash;
     - Node and yarn, when `script/bootstrap` installs them, by version.
 - Not pinned:
-    - bun, which `make build-bin` takes from `nix-shell -p bun`;
+    - bun, which `make build-bin` takes from `nix-shell -p bun`, and on Linux
+      the release build of the same bun version that it downloads;
     - `make` and `git`, which `script/bootstrap` installs from the system
       package manager when they are missing, as every `Dockerfile` stage does;
     - `bash` and `curl`, which `script/bootstrap` installs the same way when it