Route GORM's logger through slog and bound it (closes #178)

internal/middleware/middleware.go

@@ -67,6 +67,9 @@ const (
 	//	                                        ----
 	//	                                        2087
 	//
+	// The 512 is logfield.MaxBytes; the 11 is the truncation marker,
+	// charged on top of each budget rather than inside it.
+	//
 	// The fixed portion is the JSON punctuation, the field names, the
 	// level and the message, both timestamps at their longest, an IPv6
 	// remoteIP with a zone, a three-digit status and a full-width int64
@@ -104,6 +107,17 @@ const (
 	// a caller on a parameterised route would supply, which is the
 	// only way those caps can be pinned at all.
 	//
+	// One writer in that set is not a handler's own slog call. The
+	// GORM adapter in internal/gormlog logs the statement with the
+	// client-chosen parameter already interpolated into it, which on
+	// the receiver and login lookups is exactly the value the budgets
+	// above exist for. Its widest line spends two logfield.MaxBytes
+	// budgets — the statement and the driver error — against a fixed
+	// portion smaller than this one's, and
+	// internal/gormlog/gormlog_test.go asserts every line it emits
+	// against this constant directly rather than leaving it as
+	// arithmetic.
+	//
 	// What it does NOT cover, so that the figure above is not read as
 	// more than it is:
 	//
@@ -119,10 +133,16 @@ const (
 	//   - The "log" delivery target, which exists to write the whole
 	//     inbound event to the log. Deliberate; see
 	//     internal/delivery/target_log.go.
-	//   - GORM's default logger, which prints the interpolated SQL to
-	//     stdout on a record-not-found and so is unbounded on the
-	//     receiver and login lookups. NOT deliberate; filed as
-	//     https://git.eeqj.de/sneak/webhooker/issues/178.
+	//   - The widest line the service can write, which is neither an
+	//     access log line nor client-chosen. A handler panic arrives
+	//     through net/http's nil ErrorLog as one record carrying a
+	//     whole goroutine stack, above this figure — measured at
+	//     roughly 2,770 bytes. The exact width is not an invariant: it
+	//     moves with the goroutine number and with the source paths
+	//     baked into the stack. That it exceeds this ceiling does not
+	//     move. The value is the runtime's, not a client's; see
+	//     README.md and
+	//     https://git.eeqj.de/sneak/webhooker/issues/187.
 	MaxAccessLogLineBytes = 2560
 )