Re-vendor the shared files from sneak/prompts at dd4027b (closes #113)

The shared files are the sneak/prompts copies at dd4027b, with this
repository's own entries after them. make lint and make test each build
one Dockerfile phase without the cache, both covering the frontend
through a node stage; the builder stage waits on both and takes its
version from git describe unless VERSION is given. golangci-lint moves
to v2.14.0 with the new .golangci.yml; one test spells X-Request-ID as
canonicalheader asks. prettier formats only JavaScript, CSS, HTML and
Markdown, so .golangci.yml stays as fetched. script/fmt and
script/fmt-check put ~/.local/bin on PATH, which the shared workflow no
longer does. script/bootstrap keeps a Go only if it is exactly
GO_VERSION, and re-checks the go on PATH after installing.

Model: opus-5-5

script/bootstrap

@@ -6,17 +6,16 @@
 # used directly if it is at least NODE_MIN_VERSION; otherwise it is
 # installed at a pinned version via nvm (installing nvm itself first,
 # from a hash-verified release archive, never curl | sh). Go, with its
-# gofmt, is used directly if it is at least the version backend/go.mod
-# asks for; otherwise the pinned Go release is installed from its
-# hash-verified archive.
+# gofmt, is used directly only if it is exactly GO_VERSION; otherwise
+# that release is installed from its hash-verified archive.
 #
 # What this script installs outside the system package manager lives
 # under $HOME and is linked into ~/.local/bin, where make and the git
 # hook find it once that directory is on PATH. Nothing in ~/.local/bin
 # that this script did not create is ever replaced.
 #
-# golangci-lint is not installed: make lint runs it in Docker, which
-# this script does not install either.
+# golangci-lint is not installed: make lint runs it in Docker, as make
+# test runs the tests, and this script does not install Docker either.
 #
 # Unlike the org model: Go and gcc for backend/, a newer node for eslint.
 set -eu
@@ -186,20 +185,30 @@ ensure_yarn() {
 }
 
 # go_ok: the go on PATH has its gofmt beside it (a Go release ships the
-# two together) and is at least the version backend/go.mod asks for.
-# GOTOOLCHAIN=local makes an older go fail here instead of fetching a
-# newer toolchain for itself.
+# two together) and go version reports exactly GO_VERSION, compared over
+# the whole version, not a prefix of it. A go that fails or prints
+# anything else does not pass. GOTOOLCHAIN=local makes go report itself
+# rather than a toolchain it would fetch.
 go_ok() {
     if missing go; then return 1; fi
     [ -x "$(dirname "$(command -v go)")/gofmt" ] || return 1
-    (cd "$ROOT/backend" && GOTOOLCHAIN=local go list -m >/dev/null 2>&1)
+    version="$(GOTOOLCHAIN=local go version 2>/dev/null)" || return 1
+    case "$version" in
+        "go version go$GO_VERSION "*) return 0 ;;
+        *) return 1 ;;
+    esac
 }
 
 # ensure_go: unless go_ok, install GO_VERSION and link its go and gofmt.
 # They are linked on every run that needs them, so a deleted link is put
 # back, and the archive is unpacked again if either binary is missing.
+# Afterwards go is looked up through PATH again and must pass go_ok, so
+# another go that hides the link stops bootstrap.
 ensure_go() {
-    if go_ok; then return 0; fi
+    if go_ok; then
+        echo "bootstrap: using $(GOTOOLCHAIN=local go version)"
+        return 0
+    fi
     go_dir="$TOOLCHAIN/go-$GO_VERSION"
     if [ ! -x "$go_dir/bin/go" ] || [ ! -x "$go_dir/bin/gofmt" ]; then
         # sha256 of each archive, from https://go.dev/dl/?mode=json
@@ -240,6 +249,13 @@ ensure_go() {
     fi
     link_bin "$go_dir/bin/go" go
     link_bin "$go_dir/bin/gofmt" gofmt
+    hash -r
+    if ! go_ok; then
+        echo "bootstrap: after installing go $GO_VERSION in $go_dir," >&2
+        echo "  the go on PATH, $(command -v go), is not it or has no gofmt" >&2
+        exit 1
+    fi
+    echo "bootstrap: installed $(GOTOOLCHAIN=local go version)"
 }
 
 main() {
@@ -256,9 +272,9 @@ main() {
 
     if missing make; then pkg_install gnumake make make make; fi
     if missing git; then pkg_install git git git git; fi
-    # The race detector in make test needs cgo, which Go turns on only
-    # when it finds its C compiler, gcc on Linux. apt and apk ship the C
-    # library headers apart from gcc.
+    # The race detector in backend/'s make test needs cgo, which Go turns
+    # on only when it finds its C compiler, gcc on Linux. apt and apk
+    # ship the C library headers apart from gcc.
     if missing gcc; then
         pkg_install gcc "gcc libc6-dev" gcc "gcc musl-dev"
     fi
@@ -271,8 +287,8 @@ main() {
     (cd "$ROOT/backend" && go mod download)
 
     if missing docker; then
-        echo "bootstrap: docker not found; make lint, and so make check" >&2
-        echo "  and the pre-commit hook, need it to run the linters" >&2
+        echo "bootstrap: docker not found; make test and make lint, and so" >&2
+        echo "  make check and the pre-commit hook, need it" >&2
     fi
     if [ -n "$path_hint" ] && [ -d "$BIN_DIR" ]; then
         echo "bootstrap: add $BIN_DIR to the front of your PATH, e.g." >&2