fix(game): #59 — per-command rejection on PUT /api/v1/order

Validation of a player's order now applies every command against a
transient game-state snapshot and records the per-command outcome
(cmdApplied, cmdErrorCode) in each command's meta. The order is
persisted even when some commands are rejected, and the response is
202 + UserGamesOrder so clients can surface the partial failure
without the chain collapsing into "downstream service is unavailable".

Pkg/error consts are reshelved onto three explicit ranges with a
package doc and helpers (IsInternalCode/IsInputCode/IsGameStateCode):
1xxx internal/server (500/501), 2xxx structural input (400), 3xxx
game-state per-command rejection (400 when escaping HTTP, otherwise
recorded as cmdErrorCode). Two pre-existing typos fixed mechanically
(ErrBeakGroupNumberNotEnough -> ErrBreakGroupNumberNotEnough,
ErrRaceExinct -> ErrRaceExtinct) along with all callsites.

Engine errorResponse maps *GenericError by shelf rather than mapping
everything to 500. The Quit-not-last structural check in
Controller.ValidateOrder is preserved and its type assertion fixed
(was a value assertion against a pointer-typed command, so the check
silently never fired).

Backend, gateway and UI are unchanged — they were already correct on
the 202 path; only the engine collapsing per-command rejection into
500 was needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

game/internal/controller/order.go

@@ -13,17 +13,24 @@ import (
 	"github.com/google/uuid"
 )
 
-func (c *Controller) ValidateOrder(actor string, commands ...order.DecodableCommand) (err error) {
+// ValidateOrder applies every command in the order against a transient
+// view of the engine state, records the per-command outcome in each
+// command's CommandMeta via applyCommand, and reports only order-level
+// structural errors as the function return. Per-command rejections are
+// surfaced through CommandMeta.Result so the caller can persist and
+// forward them as `cmdApplied`/`cmdErrorCode` in the response body.
+func (c *Controller) ValidateOrder(actor string, commands ...order.DecodableCommand) error {
 	for i := range commands {
-		if _, ok := commands[i].(order.CommandRaceQuit); ok && i != len(commands)-1 {
-			err = e.NewQuitCommandFollowedByCommandError()
+		if _, ok := commands[i].(*order.CommandRaceQuit); ok && i != len(commands)-1 {
+			return e.NewQuitCommandFollowedByCommandError()
 		}
-		if err != nil {
-			return err
-		}
-		err = errors.Join(err, c.applyCommand(actor, commands[i]))
+		// applyCommand never returns a non-GenericError outside of
+		// programmer-error panics; the per-command code, if any, is
+		// already recorded on the command's meta and must not abort
+		// validation of the remaining commands in this order.
+		_ = c.applyCommand(actor, commands[i])
 	}
-	return
+	return nil
 }
 
 func (c *Controller) applyCommand(actor string, cmd order.DecodableCommand) (err error) {