Pin the remaining developer tool installs (closes #68)

gofumpt and protoc-gen-go are tools of a separate Go module in bin/tools,
so `go tool` builds them from source checked against bin/tools/go.sum and
mfer's own module gains no dependencies. script/bootstrap downloads that
module, and unpacks protoc 33.4 into bin/protoc from its release archive
after checking the sha256 it holds for the platform. script/generate runs
that protoc with the pinned plugin, so mfer/mf.go and its go:generate line
go. script/prettier runs only the node_modules prettier, fails when it
differs from the package.json pin, finds the node bootstrap installed
through nvm by the version in .nvmrc, and runs prettier once. Comment and
package.json fixes.

Model: opus-5-5

script/generate

@@ -4,26 +4,17 @@
 # regenerates mf.pb.go: it is committed, so building and checking need no
 # protoc. A test fails while mf.proto no longer matches the recorded hash.
 #
-# Needs exactly the protoc and protoc-gen-go versions named in the header of
-# the committed mf.pb.go (README.md says how to install them). Another
-# version writes a different mf.pb.go, so the script refuses to run.
+# Runs the protoc that script/bootstrap unpacks into bin/protoc, and the
+# protoc-gen-go that bin/tools/go.mod pins. Another version of either
+# writes a different mf.pb.go.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# protoc 33.4 names itself v6.33.4 in the mf.pb.go header.
+# The protoc version script/bootstrap installs. protoc 33.4 names itself
+# v6.33.4 in the mf.pb.go header.
 PROTOC_VERSION="33.4"
-PROTOC_GEN_GO_VERSION="v1.36.11"
-
-# require_version <command> <its exact --version output>
-require_version() {
-    actual="$("$1" --version 2>/dev/null || true)"
-    if [ "$actual" != "$2" ]; then
-        echo "generate: needs $2 on PATH, found: ${actual:-none}" >&2
-        echo "  README.md says how to install it." >&2
-        exit 1
-    fi
-}
+PROTOC="$ROOT/bin/protoc/bin/protoc"
 
 # sha256 <file>: print "<hash>  <file>", with sha256sum, or with shasum
 # where there is no sha256sum.
@@ -39,16 +30,24 @@ sha256() {
 }
 
 main() {
+    # A bin/protoc left from before the pin moved fails here, until
+    # script/bootstrap replaces it.
+    actual="$("$PROTOC" --version 2>/dev/null || true)"
+    if [ "$actual" != "libprotoc $PROTOC_VERSION" ]; then
+        echo "generate: needs protoc $PROTOC_VERSION in bin/protoc," \
+            "found: ${actual:-none}; run script/bootstrap" >&2
+        exit 1
+    fi
+    # `go tool -n` builds protoc-gen-go from bin/tools and prints where the
+    # binary is, without running it.
+    plugin="$(cd "$ROOT/bin/tools" && go tool -n protoc-gen-go)"
+
     cd "$ROOT/mfer"
-    # `go install` puts protoc-gen-go in $(go env GOPATH)/bin, which is
-    # often not on PATH.
-    PATH="$PATH:$(go env GOPATH)/bin"
-    require_version protoc "libprotoc $PROTOC_VERSION"
-    require_version protoc-gen-go "protoc-gen-go $PROTOC_GEN_GO_VERSION"
     # Hashed before regenerating, so a missing hash tool stops the script
     # before it changes anything. Regenerating leaves mf.proto as it is.
     proto_hash="$(sha256 mf.proto)"
-    go generate .
+    "$PROTOC" --plugin=protoc-gen-go="$plugin" \
+        --go_out=paths=source_relative:. ./mf.proto
     echo "$proto_hash" >mf.proto.sha256
 }