refactor(log): unified schema — mandatory type/class/method, request_id removed

Every log record now carries type ('http' for the request middleware
line, 'wrapper' for garmin execute() calls and forwarded wrapper.py
stderr, 'app' for everything else), class (Go type with package, or the
package/module for free functions), and method (the emitting Go/Python
function -- wrapper.py stamps it automatically, so its msg prefixes are
gone). msg is optional and omitted when empty; the redundant messages
('HTTP request', 'wrapper call', 'garmin wrapper stderr') are dropped,
the HTTP verb moves to http_method, source=garmin-wrapper is replaced by
type=wrapper, and the request_id middleware plumbing (applog
WithLogger/FromContext) is removed. applog.App(class, method) is the
tagging helper for app records.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/internal/log/log.go

@@ -1,12 +1,13 @@
 // Package applog provides geniusrun's structured JSON logging: a
-// log/slog-based logger writing to stdout, plus context helpers so a
-// logger enriched in one layer (e.g. internal/api's HTTP middleware,
-// attaching a request_id) is picked up by another (e.g. internal/garmin's
-// wrapper-call logging) without either package depending on the other.
+// log/slog-based logger writing to stdout, plus the App helper that tags
+// records with the mandatory schema fields every geniusrun log line
+// carries -- "type" ("app" | "http" | "wrapper"), "class" (Go type with
+// its package, or the package/module name for free functions), and
+// "method" (the Go or Python function emitting the record). "msg" is
+// optional: NewLogger's handler drops it when empty.
 package applog
 
 import (
-	"context"
 	"io"
 	"log/slog"
 	"strings"
@@ -14,9 +15,28 @@ import (
 
 // NewLogger builds a JSON-handler *slog.Logger writing to w at the given
 // level ("debug"|"info"|"warn"|"error", case-insensitive; anything else
-// defaults to info).
+// defaults to info). Empty msg values are omitted from the output --
+// records whose meaning is fully carried by type/class/method and attrs
+// (e.g. the HTTP request line) don't need one.
 func NewLogger(level string, w io.Writer) *slog.Logger {
-	return slog.New(slog.NewJSONHandler(w, &slog.HandlerOptions{Level: parseLevel(level)}))
+	return slog.New(slog.NewJSONHandler(w, &slog.HandlerOptions{
+		Level: parseLevel(level),
+		ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
+			if len(groups) == 0 && a.Key == slog.MessageKey && a.Value.String() == "" {
+				return slog.Attr{}
+			}
+			return a
+		},
+	}))
+}
+
+// App returns the default logger tagged with the mandatory schema fields
+// for an ordinary application record: type=app, plus the emitting class
+// and method. The http and wrapper emitters (internal/api's logging
+// middleware, internal/garmin's execute/forwardWrapperStderr) tag their
+// own type instead.
+func App(class, method string) *slog.Logger {
+	return slog.Default().With("type", "app", "class", class, "method", method)
 }
 
 func parseLevel(level string) slog.Level {
@@ -31,21 +51,3 @@ func parseLevel(level string) slog.Level {
 		return slog.LevelInfo
 	}
 }
-
-type ctxKey struct{}
-
-// WithLogger returns a context carrying logger, retrievable via FromContext.
-func WithLogger(ctx context.Context, logger *slog.Logger) context.Context {
-	return context.WithValue(ctx, ctxKey{}, logger)
-}
-
-// FromContext returns the logger stashed by WithLogger, or slog.Default()
-// if none was -- callers (e.g. the background incremental-sync loop, or
-// tests that don't bother injecting one) always get a working logger,
-// never nil.
-func FromContext(ctx context.Context) *slog.Logger {
-	if logger, ok := ctx.Value(ctxKey{}).(*slog.Logger); ok {
-		return logger
-	}
-	return slog.Default()
-}