fix(build): error on raw go build, require make build

Raw `go build` produces unsigned binaries that macOS kills. Add a
BuiltProperly ldflag that make build sets, and check it at startup.
If missing, print an error directing users to use make build.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Makefile

@@ -10,7 +10,8 @@ BUILD_TIME := $(shell date -u +"%Y-%m-%dT%H:%M:%SZ")
 
 LDFLAGS := -X github.com/steveyegge/gastown/internal/cmd.Version=$(VERSION) \
            -X github.com/steveyegge/gastown/internal/cmd.Commit=$(COMMIT) \
-           -X github.com/steveyegge/gastown/internal/cmd.BuildTime=$(BUILD_TIME)
+           -X github.com/steveyegge/gastown/internal/cmd.BuildTime=$(BUILD_TIME) \
+           -X github.com/steveyegge/gastown/internal/cmd.BuiltProperly=1
 
 generate:
 	go generate ./...

internal/cmd/root.go

@@ -68,6 +68,15 @@ var branchCheckExemptCommands = map[string]bool{
 
 // persistentPreRun runs before every command.
 func persistentPreRun(cmd *cobra.Command, args []string) error {
+	// Check if binary was built properly (via make build, not raw go build).
+	// Raw go build produces unsigned binaries that macOS will kill.
+	if BuiltProperly == "" {
+		fmt.Fprintln(os.Stderr, "ERROR: This binary was built with 'go build' directly.")
+		fmt.Fprintln(os.Stderr, "       Use 'make build' to create a properly signed binary.")
+		fmt.Fprintln(os.Stderr, "       Run from: ~/gt/gastown/mayor/rig (or your rig's worktree)")
+		os.Exit(1)
+	}
+
 	// Initialize CLI theme (dark/light mode support)
 	initCLITheme()
 

internal/cmd/version.go

@@ -18,6 +18,9 @@ var (
 	// Commit and Branch - the git revision the binary was built from (optional ldflag)
 	Commit = ""
 	Branch = ""
+	// BuiltProperly is set to "1" by `make build`. If empty, the binary was built
+	// with raw `go build` and is likely unsigned (will be killed on macOS).
+	BuiltProperly = ""
 )
 
 var versionCmd = &cobra.Command{