Log fx through slog, snake_case health check keys (closes #27)

fx wrote its own steps of starting and stopping as plain text to
stderr. It now logs them with its own slog event logger through the
backend's logger, so off a terminal every line from start to stop is
JSON. A config file that is found but cannot be read now makes
config.New return the error instead of panicking. A test runs the
server as a child process and checks that all it writes is JSON, on a
normal start and stop and with such a config file. The backend logs
its name, version and architecture once at start.

The health check's uptime keys are now uptime_seconds and
uptime_human, and its type and method take the names
GO_HTTP_SERVER_CONVENTIONS.md gives. Its path, content type, status
and code are unchanged.

Model: opus-5-5

TODO.md

@@ -25,16 +25,15 @@ latest run passes.
 
 - 2026-10-03: the backend's logs are one stream (issue #27): fx logs its own
   steps of starting and stopping through the backend's logger, so off a terminal
-  every line the backend's own logger and fx write is JSON, where fx used to
-  write plain text to stderr. A config file that is found but cannot be read now
-  stops the start with its error, logged as JSON like a bad setting, where it
-  used to end in a Go panic. A test runs the server as a child process and
-  checks both. The backend logs its name, version and architecture once at
-  start. The health check's uptime keys are now `uptime_seconds` and
-  `uptime_human`; its path, content type, `"status":"ok"` and 200 are unchanged.
-  `SENTRY_DSN`, `METRICS_USERNAME` and `METRICS_PASSWORD` are still read and
-  still unused, and left out of `backend/README.md`, until issues #94 and #95
-  wire them up
+  every line from start to stop is JSON, where fx used to write plain text to
+  stderr. A config file that is found but cannot be read now stops the start
+  with its error, logged as JSON like a bad setting, where it used to end in a
+  Go panic. A test runs the server as a child process and checks both. The
+  backend logs its name, version and architecture once at start. The health
+  check's uptime keys are now `uptime_seconds` and `uptime_human`; its path,
+  content type, `"status":"ok"` and 200 are unchanged. `SENTRY_DSN`,
+  `METRICS_USERNAME` and `METRICS_PASSWORD` are still read and still unused, and
+  left out of `backend/README.md`, until issues #94 and #95 wire them up
 - 2026-10-03: the frontend has a real linter (issue #47, and item 2 of issue
   #28): `eslint` with its recommended rules, set in `eslint.config.js`, runs in
   a new `frontend-lint` stage of `Dockerfile`, which the frontend stage waits

backend/cmd/netwatch-server/main_test.go

@@ -8,7 +8,6 @@ import (
 	"net/http"
 	"os"
 	"os/exec"
-	"os/signal"
 	"path/filepath"
 	"strings"
 	"syscall"
@@ -26,8 +25,6 @@ const childTimeout = 10 * time.Second
 
 func TestMain(m *testing.M) {
 	if os.Getenv(runMainEnv) != "" {
-		// A SIGTERM that comes before fx catches it is dropped, not fatal.
-		signal.Notify(make(chan os.Signal, 1), syscall.SIGTERM)
 		main()
 
 		return
@@ -49,25 +46,12 @@ func TestOutputIsJSON(t *testing.T) {
 
 	waitForHealthcheck(ctx, t, port)
 
-	// The child drops a SIGTERM that comes before fx catches it (see
-	// TestMain), so send one every 100ms until the test ends. ctx
-	// bounds the wait: when it ends, the child is killed.
-	stop := make(chan struct{})
-	defer close(stop)
+	err := child.Process.Signal(syscall.SIGTERM)
+	if err != nil {
+		t.Fatal(err)
+	}
 
-	go func() {
-		for {
-			_ = child.Process.Signal(syscall.SIGTERM)
-
-			select {
-			case <-stop:
-				return
-			case <-time.After(100 * time.Millisecond):
-			}
-		}
-	}()
-
-	err := child.Wait()
+	err = child.Wait()
 	if err != nil {
 		t.Fatalf("server exit = %v, want success", err)
 	}
@@ -119,8 +103,7 @@ func TestMalformedConfigFileStopsTheStart(t *testing.T) {
 // 127.0.0.1:port, with home as its HOME and working directory and its
 // data directory in home, so it touches nothing outside home. Its
 // stdout and stderr go to the two buffers returned, which hold all of
-// it once child.Wait returns. The child is killed when ctx ends, and
-// killed and reaped when the test ends if nothing waited for it.
+// it once child.Wait returns. The child is killed when ctx ends.
 func startServer(
 	ctx context.Context,
 	t *testing.T,
@@ -152,13 +135,6 @@ func startServer(
 		t.Fatal(err)
 	}
 
-	t.Cleanup(func() {
-		if child.ProcessState == nil {
-			_ = child.Process.Kill()
-			_ = child.Wait()
-		}
-	})
-
 	return child, &stdout, &stderr
 }