feat(ego-mgr): add lookup subcommand

ego-mgr lookup <username>
  - Finds agent whose default-username == username
  - Echoes the agent-id (map key in agent-scope)
  - Exits 7 if not found or column missing

ego-mgr/src/main.go

@@ -17,13 +17,14 @@ const (
 
 // Exit codes per spec
 const (
-	ExitSuccess        = 0
-	ExitUsageError     = 1
-	ExitColumnNotFound = 2
-	ExitColumnExists   = 3
-	ExitPermission     = 4
-	ExitLockFailed     = 5
-	ExitJSONError      = 6
+	ExitSuccess          = 0
+	ExitUsageError      = 1
+	ExitColumnNotFound  = 2
+	ExitColumnExists    = 3
+	ExitPermission      = 4
+	ExitLockFailed      = 5
+	ExitJSONError       = 6
+	ExitNotFound       = 7
 )
 
 // EgoData is the on-disk JSON structure
@@ -185,7 +186,7 @@ Examples:
   ego-mgr delete name`,
 	}
 
-	rootCmd.AddCommand(addCmd(), deleteCmd(), setCmd(), getCmd(), showCmd(), listCmd())
+	rootCmd.AddCommand(addCmd(), deleteCmd(), setCmd(), getCmd(), showCmd(), listCmd(), lookupCmd())
 
 	if err := rootCmd.Execute(); err != nil {
 		os.Exit(ExitUsageError)
@@ -480,3 +481,37 @@ func listColumnsCmd() *cobra.Command {
 	}
 	return cmd
 }
+
+func lookupCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "lookup <username>",
+		Short: "Look up an agent ID by default-username",
+		Args:  cobra.ExactArgs(1),
+		Run: func(cmd *cobra.Command, args []string) {
+			username := args[0]
+
+			data, err := readEgoData()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+				os.Exit(ExitJSONError)
+			}
+
+			// Verify default-username column exists
+			if !isAgentColumn(data, "default-username") {
+				fmt.Fprintf(os.Stderr, "Error: column 'default-username' does not exist\n")
+				os.Exit(ExitColumnNotFound)
+			}
+
+			for agentID, agentData := range data.AgentScope {
+				if agentData["default-username"] == username {
+					fmt.Print(agentID)
+					return
+				}
+			}
+
+			fmt.Fprintf(os.Stderr, "Error: no agent found with default-username '%s'\n", username)
+			os.Exit(ExitNotFound)
+		},
+	}
+	return cmd
+}